In the Sky This Month – July 2009

This feature highlights a number of meteor showers, comets and asteroids which are visible during the month of July 2009.

Note: If anyone has pictures or observations of these objects/events and want to share them, send me a comment. I’ll post them here.

Planets

Mercury - Mercury quickly drops out of view in the morning sky as the month starts. After superior conjunction (passing the Sun on its far side) on July 14, Mercury again starts to become visible low in the WNW in the evening. This apparition which is best in Aug/Sept will be great from the Southern Hemisphere but very poor from the Northern.

Saturn – Saturn is still the easiest planet to observe during the evening this month. By the end of twilight, Saturn is in the southwest under the eastern part of the constellation of Leo.

This year Saturn is dimmer than usual. At magnitude +1.0 to +1.1, there are at least a dozen or more stars that are brighter than it. The reason is the rings of Saturn contribute a lot  to the brightness of Saturn. But this year, is a ring plane crossing year meaning that the rings are nearly edge-on. As a result, the rings are reflecting much less light in the Earth’s direction this year.

Ring plane crossings occur once every half-Saturnian year (~15 years). Though the rings are over 70,000 kilometers (43,500 miles) wide, they are only 10 meters (33 feet) thick. Since the rings are seen edge, or width, on during ring plane crossings, they can actually appear to disappear in most telescopes. The last time this happened was in 1995. This year the crossing happens on Sept 4 when Saturn is too close to the Sun to be observed. Still, the rings will appear very narrow and line-like this month.

The 3-day old crescent Moon will pass a relatively distant 6 degrees to the south of Saturn on the evening of July 24.

Image of Saturn by Bob Lunsford from early May 2009.

Jupiter and Neptune - Jupiter rises late in the evening and is highest in the sky an hour or so after midnight. Other than Venus, it is the brightest “star” at dawn with a  magnitude of -2.7 to -2.8. Due to Jupiter’s location in the southern constellation of Capricornus , it never gets very high this year.

For those with a telescope or binoculars and a dark sky, Neptune is located within 1/2 to 3/4 degrees of Jupiter. Jupiter will be a bright magnitude -2.7 to -2.8 while Neptune will be a faint +7.8. That makes Jupiter over ~12,000 times brighter than Neptune. Even Jupiter’s 4 large Galilean moons are about a dozen times brighter than Neptune even though they are much smaller. The big reason for the faintness of Neptune is its distance from both the Earth and Sun. It is roughly 6 times further away from us and the Sun as Jupiter. The distance also explains its apparent small size of 2.3″. A good sized telescope will be required to see Neptune as anything other than a faint star. The Moon will pass within 3 degrees of both planets on the morning of July 10.

Image of Jupiter by Bob Lunsford from early May 2009. Note one of its moons near the left edge.

Though Neptune wasn’t discovered until 1846, it was actually observed by Galileo on two occasions in 1612 and 1613. Similar to this month’s circumstances, Jupiter was passing very close to Neptune. Galileo observed and recorded Neptune as a star in the vicinity of Jupiter. There is also evidence that he noticed that Neptune had moved but didn’t follow up on it. So when you observe these 2 planets imagine what Galileo must have been thinking nearly 400 years ago.

Uranus – Uranus is located in western Pisces. It is bright enough to be seen in small binoculars at magnitude +5.8 but will still require a telescope in order to see it as anything other than a star (it’s disk is only 3.5″ across).

Mars – Mars can be seen very low in the eastern sky all month long. At magnitude +1.1, it is only as bright as some of the brighter stars. Mars and Venus start the month within 4 degrees of each. By month’s end, the pair will be 16 degrees apart. Mars will continue to slowly brighten and become better placed for observation as the year progresses.

Venus - Venus continues to slowly climb higher every night. It is currently a morning object and is best seen an hour before sunrise low in the eastern sky. For Southern Hemisphere observers, it has already peaked for this apparition and is slowly dropping back towards the horizon. For Northern observers, Venus will continue to climb higher until early August. For binocular and telescope users, Venus is now in a gibbous phase (between half and full) and is slowly shrinking as it moves further away from Earth.

Meteors

July marks a large uptick in the level of meteor activity. The year is usually split in 2 with January through June having low rates with few major showers while July through December (really through the 1st week of January) have high rates with many major showers.

Sporadic Meteors

Sporadic meteors are not part of any known meteor shower. They represent the background flux of meteors. Except for the few days per year when a major shower is active, most meteors that are observed are Sporadics. This is especially true for meteors observed during the evening. During June, 12 or so Sporadic meteors can be observed per hour from a dark moonless sky.

Major Meteor Showers

Southern δ-Aquarids (SDA) [Date range = July 12 - Aug 19, Max = July 28]

The Southern δ-Aquarid shower is the only major shower of July producing from 10-20 meteors per hour at their peak. They are part of the Machholz complex of asteroids, comets and meteor showers that are the result of the breakup of a single comet into hundreds of smaller objects over the past thousands of years. The complex includes comet 96P/Machholz, the suspected extinct comet 2003 EH1, hundreds of Marsden and Kracht group comets, and the Quadrantid and Arietid meteor showers.

It is the comets of the Marsden group that are directly resposible for the SDA shower. These small comets have never been observed from Earth. There are only seen by spacecraft that can observe very close to the Sun. Due to the very small perihelion distance of these comets (~0.05 AU) they only get bright enough to be discovered when close to the Sun. Currently there are ~33 comets that are known to be members of the Marsden group.

The shower radiates from RA = 22h 36m, Dec = -16 deg.

Minor Meteor Showers

Minor showers produce so few meteors that they are hard to notice above the background of regular meteors.

Piscis Austrinids (PAU) [Date range = July 15 - Aug 10, Max = July 27]

This shower of unknown parentage is a difficult one for northern observers due to the southern location of its radiant (RA = 22h 44m, Dec = -30deg). Similar to the SDAs and the CAPs below, it is active from mid-July to mid-August with a maximum around July 27. At maximum one can expect 2-4 meteors per hour from a dark site. Rates will be even lower for northern observers.

α-Capricornids (CAP) [Date range = July 3 - Aug 15, Max = July 29]

The CAP is yet another southern shower (RA = 20h 28m, Dec = -10 deg) that is difficult to observe from northern latitudes. With a peak on July 29, it can be expected to produce 3-6 meteors per hour. Unlike the PAUs, the CAPs appear to be associated with a known comet, 169P/NEAT.

Perseids (PER) [Date range = July 17 - Aug 24, Max = Aug 12]

The Perseids are one of the best meteor showers of the year and never disappoint… in August. During July, the shower is a consistent producer of a small number of showers as it slowly builds toward its August 12 peak. Expect to see a meteor or 2 per hour from the Perseids during the 2nd half of July. This is way short of the 60-120 meteors per hour that can be seen at its peak though this year the near Full Moon will cut down on those rates.

Comets

Naked Eye Comets (V < 6.0)

None

Binocular Comets (V = 6.0 – 8.0)

Comet C/2008 Q3 (Garradd)

This is the surprise comet of the summer. From time to time what appears to be a faint run-of-the-mill comet will undergo an outburst and brighten substantially. This is the case with Comet Garradd which was discovered by Gordon Garradd of the Siding Spring Survey (Australia). He used the 0.5-m Uppsala schmidt telescope to discover this comet back on 2008 August 27.

The comet was a faint 19th magnitude at discovery. With perihelion expected on 2009 June 23 at 1.80 AU from the Sun, it was expected to brighten but only to about 12th-14th magnitude. Two weeks ago the comet was sitting at 15th magnitude. Bright enough for CCD imaging but too faint for nearly all visual observers. On April 20th Micheal Jager imaged the comet and found it too be much brighter. Over the next few days, visual observers were able to confirm the outburst and estimated the comet to be as bright as magnitude 8.9.

Now more than a month after its outburst, the comet continues to brighten and has recently been estimated at magnitude 7.0. With perihelion this month, the comet should be as bright as it gets though one never knows with outburst comets.

The comet is now visible from both Hemispheres. It travels northward from Corvus into Virgo in the evening sky.

A finder chart for Comet Garradd can be found at Comet Chasing.

A nice collection of images can be found at the VdS-Fachgruppe Kometen (Comet Section of Germany) and Seiichi Yoshida’s Comet Homepage.

Small Telescope Comets (V = 8.0 – 10.0)

Comet C/2006 W3 (Christensen)

This comet was discovered over 2 years ago on 2006 November 18 by Eric Christensen of the Catalina Sky Survey north of Tucson. At the time the comet was located at 8.7 AU from the Sun which is nearly the distance of Saturn. The comet continues to move closer to the Sun and Earth and is currently 3.8 AU from the Sun and 3.4 AU from the Earth.

The comet is currently around magnitude 8.5 and should be at its brightest this month.  It is moving near the border of Pegasus and Cygnus.  The comet is best seen after 10 pm.

The comet will reach perihelion at a rather distant 3.12 AU from the Sun on 2009 July 6. Christensen should remain bright enough to see in modest sized backyard telescopes for all of 2009.

On the morning of April 21, I was able to observe this comet with both 30×125 binoculars and a 12″ dobsonian. The comet was much easier to see in the 12″. Observation was made under a moderately light polluted sky with a limiting mag of ~+5.5.

A finder chart for Comet Christensen can be found at Comet Chasing and Aktuelle Kometen (in German).

A nice collection of images can be found at the VdS-Fachgruppe Kometen (Comet Section of Germany) and Seiichi Yoshida’s Comet Homepage.

Comet C/2008 T2 (Cardinal)

Rob Cardinal, an astronomer at the University of Calgary in Canada, discovered this comet last October. The comet was discovered as part of a survey at  the Rothney Astrophysical Observatory for new Near-Earth asteroids at high declinations. In fact the comet was found within 10 degrees of the North celestial pole. At the time of discovery, the comet was ~14th magnitude.

At perihelion on June 13th, the comet passed within 1.20 AU of the Sun. The comet can only be seen from the Southern Hemisphere as it is located south of the Sun. The comet is currently magnitude 8.5 to 9.0 as it moves southeast from Canis Minor into Antilia in the evening sky. It is too bad the comet is located so far from Earth. At a distance of 1.8 AU from Earth, it is located on the other side of the Sun. If this comet has approached as close as Comet Lulin (0.4 AU) did, Comet Cardinal would be shining at 5th magnitude and be visible to the naked eye from dark locations.

A finder chart for Comet Cardinal can be found at Comet Chasing.

A nice collection of images can be found at the VdS-Fachgruppe Kometen (Comet Section of Germany) and Seiichi Yoshida’s Comet Homepage.

22P/Kopff

All of the above comets are long-period comets which will not return to the inner Solar System for thousands to millions of years. Comet Kopff is a frequent visitor with an orbital period of 6.4 years. Discovered on 1906 August 20 by August Kopff of Germany, the comet has been observed during every subsequent return except one.

The comet reached perihelion at 1.58 AU from the Sun on May 25. Though now moving away from the Sun, the comet still moving closer to Earth and will be located 0.78 AU from us at the end of the month. Recent observations place the comet at magnitude 9.5 which is about as bright as it will get this apparition. The comet spends July in Aquarius.

A finder chart for Comet Kopff can be found at Comet Chasing.

A nice collection of images can be found at the VdS-Fachgruppe Kometen (Comet Section of Germany) and Seiichi Yoshida’s Comet Homepage.

Asteroids

Binocular and Small Telescope Asteroids (V < 10.0)

(3) Juno

Juno was the 3rd asteroid to be discovered after (1) Ceres and (2) Pallas. It was found by German astronomer Karl Harding on September 1, 1804. With dimensions of 320×267×200 km (192 x 160 x 120 miles) Juno ranks as the 10th largest asteroid in the Main Belt though it is the 2nd largest stony S-type asteroid.

This month it will be moving slowly eastward through Pisces while brightening from magnitude 9.7 to 9.1. Peak brightness will come at opposition on Sept. 22 when Juno will be as bright as magnitude 7.6. A few degrees to the eats of Juno is another bright asteroid, (18) Melpomene which is described in its own section.

A finder chart (needs to be flipped upside down for Northern Hemisphere observers) can be found at the Royal Astronomical Society of New Zealand. Finder chart for Juno from Heavens Above.

(7) Iris

Iris is an inner Main-Belt asteroid that can occasionally get as bright as any asteroid. This year, Iris will not get as bright but will still become a binocular object (albeit a difficult one) at opposition on July 4 at magnitude 8.7. During July, it is located in the constellation of Sagittarius at magnitude 8.8 at the start of the month and magnitude 9.3 at the end. On the nights of July 23/24/25 UT, Iris will pass in front of the bright open star cluster M25 for a nice photo-op.

With a size of 240 x 200 x 200 km, Iris is the 5th largest stoney S-type asteroid. It was discovered in 1847 by John Russel Hind, the 1st of 10 asteroids he discovered.

A finder chart (needs to be flipped upside down for Northern Hemisphere observers) can be found at the Royal Astronomical Society of New Zealand. Finder chart for Iris from Heavens Above.

(18) Melpomene

Just a few degrees to the east of (3) Juno lies another nice asteroid target for small telescopes. (18) Melpomene is also located in the constellation of Pisces and is only a little bit fainter than Juno, brightening from magnitude 10.0 to 9.4 in July.

Melpomene is another stoney S-type asteroid and similar to Iris was also discovered by John Russel Hind. Found in 1852, it is his 5th of 10 asteroid discoveries.

A finder chart (needs to be flipped upside down for Northern Hemisphere observers) can be found at the Royal Astronomical Society of New Zealand. Finder chart for Iris from Heavens Above.

In The Sky This Month – May 2009

This feature highlights a number of meteor showers, comets and asteroids which are visible during the month of May 2009.

Note: If anyone has pictures or observations of these objects/events and want to share them, send me a comment. I’ll post them here.

Planets

Mercury - Last month saw Mercury’s best evening apparition of 2009 (at least for Northern Hemisphere observers). Mercury is now descending back into the glow of the Sun. For the first week or so of the month it is still visible low in the west during evening twilight. Unlike last month, it is much fainter now (+0.9 magnitude on the 1st, +3.7 on the 11th).

Saturn – Saturn is the easiest planet to observe in May. By the end of twilight, Saturn is just south of zenith (straight up) under the eastern part of the constellation of Leo.

This year Saturn is dimmer than usual. At magnitude +0.8 to +0.9, there are at least a dozen stars that are brighter than it. The reason is the rings of Saturn contribute a lot  to the brightness of Saturn. But this year, is a ring plane crossing year meaning that the rings are nearly edge-on. As a result, the rings are reflecting much less light in the Earth’s direction this year. Saturn’s appearance through a telescope will match the below image taken on April 23.

Image of Saturn by C. Hergenrother. April 23 w/ 12" with DMK41AF02 camera.

The Moon will pass a relatively distant 5.5 degrees to the south of Saturn on the evening of May 3.

Venus - Venus continues to slowly climb higher every night. It is currently a morning object and is best seen an hour before sunrise low in the eastern sky. For Southern Hemisphere observers, it will reach its highest point during the 2nd half of the month. For Northern observers, Venus will continue to climb higher until early August.

For binocular and telescope users, Venus will start the month as a large fat crescent, 39″ across and only 25% illuminated. By the end of the month, it will have shrunk to 25″ across but will also be nearly half illuminated at 46%.

Jupiter and Neptune - Jupiter rises a few hours before sunrise. By the end of the month, the king of the planets peaks above the horizon a little after midnight. Other than Venus, it is the brightest “star” in the morning sky at magnitude -2.2 to -2.4. Due to Jupiter’s location in the southern constellation of Capricornus , it never gets very high this year.

For those with a telescope or binoculars and a dark sky, Jupiter will pass close to the planet Neptune on the morning of May 27. At their closest, the 5th and 8th planet will only be 0.39 degrees apart. Jupiter will be a bright magnitude -2.4 while Neptune will be a faint +7.9. That makes Jupiter nearly ~12,000 times brighter than Neptune. Even Jupiter’s 4 large Galilean moons are about a dozen times brighter than Neptune even though they are much smaller. The big reason for the faintness of Neptune is its distance from both the Earth and Sun. It is roughly 6 times further away from us and the Sun as Jupiter. It’s distance also explains its apparent small size of 2.3″. A telescope will be required to see Neptune as anything other than a faint star.

Though Neptune wasn’t discovered until 1846, it was actually observed by Galileo on two occasions in 1612 and 1613. Similar to this month’s circumstances, Jupiter was passing very close to Neptune. Galileo observed and recorded Neptune as a star in the vicinity of Jupiter. There is also evidence that he noticed that Neptune had moved but didn’t follow up on it. So when you observe these 2 planets imagine what Galileo must have been thinking nearly 400 years ago.

Uranus – Uranus is located in western Pisces. It is bright enough to be seen in small binoculars at magnitude +5.9 but will still require a telescope in order to see it as anything other than a star (it’s disk is only 3.4″ across).

Both planets are early morning objects low in the southeastern sky.

Mars – Mars can be seen very low in the eastern sky all month long. At magnitude +1.2, it is only as bright as some of the brighter stars. Venus passed a distant 4 degrees to the north of Mars on April 24. Mars and Venus will continue to move apart until around mid-month when they will be 6.5 degrees apart. After that their distance from each other will shrink as they approach a 2 degree conjunction on June 21.

Meteors

The month of March experiences no major showers and only a few minor ones. It continues the annual lull in meteor activity from mid-January to mid-April.

Sporadic Meteors

Sporadic meteors are not part of any known meteor shower. They represent the background flux of meteors. Except for the few days per year when a major shower is active, most meteors that are observed are Sporadics. This is especially true for meteors observed during the evening. During April, 8 or so Sporadic meteors can be observed per hour from a dark moonless sky.

Major Meteor Showers

Eta Aquarids (ETA)

The Eta Aquarids are a major shower, especially for southern hemisphere observers, when they peak on May 5. For northern observers, the shower will only be observable for an hour or two before dawn. Since the radiant doesn’t get very high for NH observers, rates can be low. The radiant is located near the “jar” of Aquarius.

The ETA were produced by Comet Halley which also gives us the Orionids in October. Models suggest that the ETA were released by Comet Halley no later than 837 AD. The Orionids are easy to see because the particles are hitting the Earth from the anti-solar direction. This means the meteor shower can be seen in the middle of the night. The ETA are produced by meteoroids moving outbound from the Sun, as a result the radiant is located relatively close to the Sun. This means that the ETA radiant is only visible for an hour or so before twilight. By luck, the nearly Full Moon will have just set making the last hour of the night dark.

The shower spans from April 19 to May 28 with a peak around May 5 with a maximum ZHR of ~60.

Additional information on these showers and other minor showers not included here can be found at the following sites: Robert Lunsford’s Meteor Activity Outlook, Wayne Hally’s and Mark Davis’s NAMN Notes, and the International Meteor Organization’s 2008 Meteor Shower Calendar.

Minor Meteor Showers

Minor showers produce so few meteors that they are hard to notice above the background of regular meteors.

Eta Lyrids (ELY)

This shower is associated with Comet C/1983 H1 (IRAS-Araki-Alcock). The comet is a long-period comet which passed within 0.03 AU of the Earth on 1983 May 11. Discovered by astronomers using the Infrared Astronomical Satellite (IRAS) and two amateur astronomers, Genichi Araki (Yuzawa, Niigata, Japan) and George Alcock (Peterborough, England, UK), the comet brightened to 1st magnitude for a few days around closest approach.

Though the comet is now long gone and will not return for quite some time, particles released during past perihelia can be observed every year in early May. The Eta Lyrids are a minor shower that have never produce more than ~3 meteors per hour. Peak time in on May 8 though some meteors can be seen from May 3-12. Meteors will appear to radiate from a point in the middle of a triangle made up of the bright stars Vega and Deneb and the “head” of the constellation Draco. The Moon, Full on May 7, will spoil the Eta Lyrids for this year.

Comets

Naked Eye Comets (V < 6.0)

None

Binocular Comets (V < 8.0)

None

Small Telescope Comets (V < 10.0)

Comet C/2009 F6 (Yi-SWAN)

Comet C/2009 F6 (Yi-SWAN) is a long-period comet which will pass within 1.27 AU of the Sun on May 7. The comet is currently around magnitude 8.5 making it bright enough to be seen in small telescopes. Right now the nearly Full Moon will make observing the comet difficult but in a few days the Moon will not be a problem for evening observers. The comet is located northeast of the Sun. For southern hemisphere observers, you are out of luck. For northern observers, the comet can be observed in the evening sky.

The comet starts the month in Perseus. As it travels to the southeast, it will enter Auriga by the last week of the month. The comet will never get far from the horizon so a clear dark northwestern horizon is a must to see this comet. By mid-month the comet will be too close to the Sun for easy observation.

On the morning of April 21, I was able to observe Yi-SWAN with 30×125 binoculars. My observing location isn’t too dark with a limiting magnitude of ~+5.5. Even then, the summer Milky Way was faintly visible. The comet was barely visible as it was large and diffuse. Interestingly, the comet was not visible during multiple attempts to observe it during the evening hours. The darker morning sky most definitely helped. Unfortunately, in May the comet will not be visible in the morning.

The comet was found by Dae-am Yi of Yeongwol-kun, Gangwon-do, South Korea on March 26. He noticed the obvious blue-green glow of a comet on 2 images he took with a Canon 5D digital camera and a 90-mm f/2.8 lens. The other discoverer was Robert Matson of Irvine, CA. Mr. Matson found the comet on a series of images taken with the SWAN instrument on the SOHO (Solar Heliospheric Observatory) spacecraft starting on March 29.

A finder chart for Comet Yi-SWAN can be found at Comet Chasing and Aktuelle Kometen (in German).

A nice collection of images can be found at the VdS-Fachgruppe Kometen (Comet Section of Germany) and Seiichi Yoshida’s Comet Homepage.

Comet C/2008 Q3 (Garradd)

Sometimes comets surprise us. From time to time what appears to be a faint run-of-the-mill comet will undergo an outburst and brighten substantially. This is the case with Comet Garradd. Gordon Garradd of the Siding Spring Survey (Australia) used the 0.5-m Uppsala schmidt telescope to discover this comet back on 2008 August 27.

The comet was a faint 19th magnitude at discovery. With perihelion expected on 2009 June 23 at 1.80 AU from the Sun, it was expected to brighten but only to about 12th-14th magnitude. Two weeks ago the comet was sitting at 15th magnitude. Bright enough for CCD imaging but too faint for nearly all visual observers. On April 20th Micheal Jager imaged the comet and found it too be much brighter. Over the next few days, visual observers were able to confirm the outburst and estimated the comet to be as bright as magnitude 8.9.

Whether the comet will continue in its excited state and brighten further as it approaches perihelion is not known. It’s possible that the outburst will be short-lived and the comet may revert back to its original activity level.

Right now this comet is only observable from the Southern Hemisphere as it rockets through the constellations of Indus, Pavo, Apus, Triangulum Australe, and Circinus. For us up north, the comet will become visible in June as an evening object.

I hope to have a link to a finder chart for this comet up soon.

Comet C/2006 W3 (Christensen)

This comet was discovered over 2 years ago on 2006 November 18 by Eric Christensen of the Catalina Sky Survey north of Tucson. At the time the comet was located at 8.7 AU from the Sun which is nearly the distance of Saturn. The comet continues to move closer to the Sun and Earth and is currently 3.8 AU from the Sun and 3.4 AU from the Earth.

The comet is currently around magnitude 9.5 and will slowly brighten during the month.  It is moving near the border of Lacerta and Pegasus.  The comet is best seen in the early morning.

The comet will continue to brighten as it approaches perihelion at a still rather distant 3.12 AU from the Sun on 2009 July 6. At that time, the comet will be 8th magnitude and visible in many smaller backyard telescopes and even binoculars from dark sites. Christensen should remain bright enough to see in modest sized backyard telescopes for all of 2009.

On the morning of April 21, I was able to observe this comet with both 30×125 binoculars and a 12″ dobsonian. The comet was much easier to see in the 12″. Observation was made under a moderately light polluted sky with a limiting mag of ~+5.5.

A finder chart for Comet Christensen can be found at Comet Chasing and Aktuelle Kometen (in German).

A nice collection of images can be found at the VdS-Fachgruppe Kometen (Comet Section of Germany) and Seiichi Yoshida’s Comet Homepage.

Comet C/2009 G1 (STEREO)

Jiangao Ruan of China found this comet on images taken by the SECCHI HI-1B instrument onboard one of the STEREO spacecraft. The comet was first visible on images taken on April 3 UT. Similar to SOHO (a spacecraft that was used to co-discover Comet C/2009 F6 (Yi-Swan)), the two STEREO spacecraft study the Sun and its immediate environment.

With perihelion on April 16 at 1.13 AU from the Sun, the comet is now moving away from the Sun. Luckily it is still moving closer to the Earth, though it will get no closer than 1.06 AU from Earth. With a current estimated magnitude of ~9.0, the comet may brighten a bit as it gets closer.

The comet starts the month in southern Aquarius and will pass through Sculptor before finishing the month in the far southern constellation of Phoenix. It was never an easy object for northern observers and is now only observable from southern latitudes.

A finder chart for Comet STEREO can be found at Comet Chasing.

A nice collection of images can be found at Seiichi Yoshida’s Comet Homepage.

Comet C/2009 E1 (Itagaki)

This comet was found by amateur astronomer Koichi Itagaki of Yamagata, Japan on March 14. Comet C/2009 E1 (Itagaki) is a long-period comet which will come within 0.60 AU of the Sun at perihelion on April 7. It is also periodic in that it returns once every ~250 years according to the latest orbit.

This is the 1st comet to bear Koichi Itagaki’s name but it is not his 1st discovery. Back in 1968, he was a co-discoverer of Comet Tago-Honda-Yamamoto. Due to the rule that only the 1st 3 discoverers can have their name attached to a comet, his name was left off. Only a few months ago, he also re-discovered long-lost comet Giacobini.

The comet is located in the morning sky moving through Andromeda and to just north of the “square” of Pegasus. Due to its proximity to the Sun over the past few weeks, it hasn’t been observed since early April. At the time, it was magnitude 7.5-8.0. If it is still in the magnitude ~8.0 to 8.5 range then the  comet will bright enough to be seen in a reasonably sized backyard telescope.

A finder chart for Comet Itagaki can be found at Comet Chasing.

A nice collection of images can be found at the VdS-Fachgruppe Kometen (Comet Section of Germany).

Comet C/2008 T2 (Cardinal)

Rob Cardinal, an astronomer at the University of Calgary in Canada, discovered this comet last October. The comet was discovered as part of a survey at  the Rothney Astrophysical Observatory for new Near-Earth asteroids at high declinations. In fact the comet was found within 10 degrees of the North celestial pole. At the time of discovery, the comet was ~14th magnitude.

At perihelion on June 13th of this year, the comet will pass within 1.20 AU of the Sun. The comet is currently ~9.0 to 9.5 magnitude as it moves south across Gemini into Canis Minor in the evening sky. The comet should continue to brighten by another magnitude this month. Similar to most comets, access to a clear western horizon is necessary to see it.

A finder chart for Comet Cardinal can be found at Comet Chasing and Aktuelle Kometen (in German).

A nice collection of images can be found at the VdS-Fachgruppe Kometen (Comet Section of Germany) and Seiichi Yoshida’s Comet Homepage.

Asteroids

Binocular and Small Telescope Asteroids (V < 10.0)

(1) Ceres

Ceres is the biggest asteroid in the Main Belt with a diameter of 585 miles or 975 km. It is so big that it is now considered a Dwarf Planet. Classified as a carbonaceous (carbon-rich) Cg-type asteroid, there are suggestions that it may be rich in volatile material such as water. Some even propose that an ocean exists below its surface. Ceres is one of two targets for NASA’s Dawn spacecraft which is scheduled to visit it in 2015. This month Ceres fades from from magnitude 8.0 to 8.4 as it ends is retrograde motion just north of Leo. If you are observing Saturn with a telescope or pair of binoculars, try your hand at finding Ceres with one of the finder charts linked below.

A finder chart (needs to be flipped upside down for Northern Hemisphere observers) can be found at the Royal Astronomical Society of New Zealand. Finder chart for Ceres from Heavens Above.

(8) Flora and (14) Irene

Irene was discovered by John Russel Hind in 1851, being only the 14th asteroid known at the time (if you are wondering ~400,000 asteroids have been discovered to date, we’ve come a long way). It is an S-type asteroid with a stoney or silicate composition. Its takes 6.3 years to orbit the Sun. This month Irene will fade from magnitude 9.0 to 9.7 as it moves through central Virgo.

Though it is a bit fainter than the asteroids I usually present, those up for a challenge can spot the asteroid (8) Flora a few degrees away from Irene.

Flora is a large asteroid roughly 136×136x113 km in dimension. It is innermost large asteroid in the Main Belt. As a result, it can get bright enough for backyard observers with modest sized telescopes and binoculars. Flora is a stoney S-type asteroid and also the largest member of the Flora family. This family was created when a large impact occured on Flora. The other family members are pieces of Flora that were thrown off by the impact.

Flora starts the month at magnitude 9.9. By the end of the month, it has faded to 10.5. Flora and Irene provide us with a 2-for since both objects are located within 5 degrees of each other.

Since I have not been able to find a nice star chart showing the position of Irene and Flora, here is one I made with the C2A program. The bright star that Flora passes close to towards the end of the month (right side of the chart, white circle) is zeta Virginis.

In The Sky This Month – 2009 April

This feature highlights a number of meteor showers, comets and asteroids which are visible during the month of April 2009. The month sees the return of the borderline major meteor shower, the Lyrids. The highlight of the month is the lunar occultation of Venus right before dawn on April 22.

Note: If anyone has pictures or observations of these objects/events and want to share them, send me a comment. I’ll post them here.

Planets

Mercury - This month brings us the best opportunity of the year to observe Mercury in the evening sky (for Northern Hemisphere observers). Mercury will be at its highest on April 26, though even then it will be low in the western sky 30-60 minutes after sunset.

The Moon will also located just above Mercury on the evening of April 26. The image below shows what the scene will look like from North America. Note that the Pleiades open star cluster will be located between Mercury and the Moon. It will be a great sight via your eye or binoculars. In a telescope, Mercury will appear as a fat crescent with ~36% of its disk illuminated.

Map of the Moon-Mercury-Pleiades conjunction on the evening of April 26. Map made with Stellarium.

Saturn – Saturn is the only planet visible in the evening sky. By the end of twilight, Saturn is high in the southeast under the eastern part of the constellation of Leo.

This year Saturn is dimmer than usual. At magnitude +0.6 to +0.7, there are at least 11 stars that are brighter than it. The reason is that the rings of Saturn contribute a lot  to the brightness of Saturn. But this year, is a ring plane crossing year meaning that the rings are nearly edge-on. As a result, the rings are reflecting much less light in the Earth’s direction this year. Saturn’s appearance through a telescope will match the below image taken by Bob Lunsford on March 28. Note the small dark spot near the top edge of Saturn’s disk, this is a shadow cast by Saturn’s largest moon, Titan.

Image of Saturn by Bob Lunsford from 2009 March 28. Titan's shadow seen near top.

The Moon will pass a relatively distant 5.5 degrees to the south of Saturn on the evening of April 6.

Venus - After spending the past few months dominating the evening sky, Venus will now spend the rest of the year as a morning object. If you live south of the Equator, Venus will appear to rocket higher and higher every morning. In fact it should be an easy sight by the 2nd week of April if you have a clear eastern horizon. Venus will reach its highest in late May.

For those of us north of the Equator, Venus will take a little longer to gain altitude. Though it is already visible for observers with a clear eastern horizon, Venus will slowly climb higher every night. For  northern observers, Venus won’t reach its highest till August. Regardless of where you are observing, Venus will be at its brightest on April 29 though it is always a very bright object.

For binocular and telescope users, Venus will start the month as a large thin crescent, 59″ across and only ~2% illuminated. By mid-month, it will have shrunk to ~50″ across but it will also become a fatter crescent with ~12% of the disk illuminated. By the end of the month, it is 39″ across and 25% illuminated

Venus is also involved in the coolest event of the month. On the morning of April 22, the Moon will occult (or pass in front) of Venus for observers in most of North America. The below map from the International Occultation Timing Association (IOTA) shows where the occultation will be visible. Times for the beginning and end of the occultation can be found at IOTA’s site. I’ll write more about this as the date draws closer.

The following diagram gives a good representation of what the occultation will look like right before the Moon passes in front of Venus on the morning of April 22. Note that Mars will be located nearby as well. For those with binoculars or a telescope, Venus will appear as a thin crescent similar to, but much smaller than, the Moon.

The Moon, Venus and Mars just before the start of the occulatation of Venus on the morning of April 22. Sky map produced with Stellarium.

Jupiter - Jupiter rises a few hours before sunrise. Other than Venus, it is the brightest “star” in the morning sky at magnitude -2.2. Due to Jupiter’s location in the southern constellation of Capricornus , it never gets very high this year.

Mars – Mars can be seen very low in the eastern sky all month long. At magnitude +1.2, it is only as bright as some of the brighter stars. Venus will pass a distant 5.5 degrees to the north of Mars on April 24. As a result, Mars will be located just below the spectacular Moon-Venus occultation.

Meteors

The month of March experiences no major showers and only a few minor ones. It continues the annual lull in meteor activity from mid-January to mid-April.

Sporadic Meteors

Sporadic meteors are not part of any known meteor shower. They represent the background flux of meteors. Except for the few days per year when a major shower is active, most meteors that are observed are Sporadics. This is especially true for meteors observed during the evening. During April, 8 or so Sporadic meteors can be observed per hour from a dark moonless sky.

Major Meteor Showers

Lyrids (LYR)

April brings the first major meteor shower since the Quadrantids in early January. The Lyrids are produced by Comet Thatcher, a comet on a ~400 years orbit that has only been observed in 1861. The Lyrids, on the other hand, can be seen every year.

The radiant is located between the constellations of Lyra and Hercules. Though the radiant rises during the evening, the best time to see Lyrids is after 11 pm when the radiant is high in the sky.

The shower is active from April 16 to 25 with a peak on the morning of April 22. The shower only shows good levels of activity on the night of the peak. Even then, this is the most minor of the major showers with a peak rate of ~15-25 meteors per hour.

Though there are no predictions on enhanced activity, the Lyrids have been known to put on grand displays. The 1st great display goes back almost 25oo years while the last happened in 1982. So you never know, this year could be the next good display.

Minor Meteor Showers

Minor showers produce so few meteors that they are hard to notice above the background of regular meteors.

Pi Puppids (PPI)

The Pi Puppids are usually a very low activity shower. In 1977 and 1982, the shower put on a good display with up to 60 meteors per hour being observed. This shower radiates from the far southern constellation of Puppis and can not be seen from most of North America and Europe.

We now know that the Pi Puppids are created by Comet 26P/Grigg-Skjellerup. P/G-S is a small Jupiter family comet that orbits the Sun once every 5.3 years.

There are no predictions for enhanced material this year. The shower is active from April 15-28 with a peak on April 23. At its best we should expect 1-2 meteors per hour with even that number being optimistic for northern observers.

Eta Aquarids (ETA)

The Eta Aquarids are a major shower, especially for southern hemisphere observers, when they peak on May 5. During the month of April, the shower can be considered a minor shower.

The ETA were produced by Comet Halley which also gives us the Orionids in October. Models suggest that the ETA were released by Comet Halley no later than 837 AD. The Orionids are easy to see because the particles are hitting the Earth from the anti-solar direction. This means the meteor shower can be seen in the middle of the night. The ETA are produced by meteoroids moving outbound from the Sun, as a result the radiant is located relatively close to the Sun. This means that the ETA radiant is only visible for an hour or so before twilight.

The shower spans from April 19 to May 28 with a peak around May 5 with a maximum ZHR of ~60. The last week of April will see some low activity (ZHR < 10) from the ETAs.

Additional information on these showers and other minor showers not included here can be found at the following sites: Robert Lunsford’s Meteor Activity Outlook, Wayne Hally’s and Mark Davis’s NAMN Notes, and the International Meteor Organization’s 2008 Meteor Shower Calendar.

Comets

Naked Eye Comets (V < 6.0)

None

Binocular Comets (V < 8.0)

None

Small Telescope Comets (V < 10.0)

Comet C/2009 E1 (Itagaki)

This recently discovered comet was found by amateur astronomer Koichi Itagaki of Yamagata, Japan. Comet C/2009 E1 (Itagaki) is a long-period comet which will come within 0.60 AU of the Sun at perihelion on April 7. It is also periodic in that it returns once every ~250 years according to the latest orbit.

This is the 1st comet to bear Koichi Itagaki’s name but it is not his 1st discovery. Back in 1968, he was a co-discoverer of Comet Tago-Honda-Yamamoto. Due to the rule that only the 1st 3 discoverers can have their name attached to a comet, his name was left off. Only a few months ago, he also re-discovered long-lost comet Giacobini.

The comet is located in the evening sky north of the constellation of Aries. As the month progresses the comet will move north of the Sun as it travels through Triangulum, northern Pisces and Andromeda. Only observers with a clear view of the northwestern horizon in the evening and northeastern horizon in the morning will be able to see the comet. By May the comet will only be visible in the morning sky and will be much easier to see.

At magnitude ~8.0 to 8.5, the comet is bright enough to be seen in a reasonably sized backyard telescope. Having said that, I was just barely able to see it from my backyard in Tucson with my 12″ telescope due to the city lights and the bright twilight.

A finder chart for Comet Itagaki can be found at Comet Chasing.

A nice collection of images can be found at the VdS-Fachgruppe Kometen (Comet Section of Germany).

Comet C/2009 F6 (Yi-SWAN)

A new comet has been discovered that should be the brightest comet in the sky this month. Comet C/2009 F6 (Yi-SWAN) is a long-period comet which will pass within 1.27 AU of the Sun on May 8. The comet is currently around magnitude 8.5 making it bright enough to be seen in small telescopes. Right now the nearly Full Moon will make observing the comet difficult but in a few days the Moon will not be a problem for evening observers. The comet is located north of the Sun. For southern hemisphere observers, you are out of luck. For northern observers, the comet can be observed in both the evening and morning sky.

Currently the comet is located in Cassiopeia. It is moving to the east and will enter Perseus by mid-month. The comet should continue to brighten as it approaches perihelion and may be as bright as magnitude 8.0.

On the morning of April 21, I was able to observe Yi-SWAN with 30×125 binoculars. My observing location isn’t too dark with a limiting magnitude of ~+5.5. Even then, the summer Milky Way was faintly visible. The comet was barely visible as it was large and diffuse. Interestingly, the comet was not visible during multiple attempts to observe it during the evening hours. The darker morning sky most definitely helped.

The comet was found by Dae-am Yi of Yeongwol-kun, Gangwon-do, South Korea on March 26. He noticed the obvious blue-green glow of a comet on 2 images he took with a Canon 5D digital camera and a 90-mm f/2.8 lens. The other discoverer was Robert Matson of Irvine, CA. Mr. Matson found the comet on a series of images taken with the SWAN instrument on the SOHO (Solar Heliospheric Observatory) spacecraft starting on March 29. The SWAN insturment images the entire sky for solar Lyman-alpha particles that are backscattered off of neutral hydrogen atoms. In this way, SWAN can monitor the activity of the far-side of the Sun. This instrument is also excellent at detecting the glow of hydrogan in the extended coma of comets.

Comet C/2007 N3 (Lulin)

Comet Lulin was discovered by the Lulin Sky Survey in Taiwan on 2007 July 11. At the time the comet was located beyond the orbit of Jupiter. The comet will be closest to the Sun on 2009 January 10 at 1.21 AU from the Sun. It will be closest to Earth in late-February when it will be only 0.41 AU from us.

The comet is fading after its closest approach to Earth in late February. It is a evening object and spends all of April moving westward through western Gemini. The comet starts the month around magnitude 8.5 and should fade to magnitude 10.0 or fainter by the end of the month.

A finder chart for Comet Lulin can be found at Comet Chasing.

A nice collection of images can be found at the VdS-Fachgruppe Kometen (Comet Section of Germany) and Seiichi Yoshida’s Comet Homepage.

Comet C/2006 W3 (Christensen)

This comet was discovered over 2 years ago on 2006 November 18 by Eric Christensen of the Catalina Sky Survey north of Tucson. At the time the comet was located at 8.7 AU from the Sun which is nearly the distance of Saturn. The comet continues to move closer to the Sun and Earth and is currently 3.8 AU from the Sun and 3.4 AU from the Earth.

The comet is currently around magnitude 9.5 and will slowly brighten during the month.  It is moving near the border of Lacerta and Pegasus.  The comet is best seen in the early morning. I was able to observe the comet visually with my backyard 12″ reflecting telescope back in November. Being small and condensed, the comet was fairly easy to see.

The comet will continue to brighten as it approaches perihelion at a still rather distant 3.12 AU from the Sun on 2009 July 6. At that time, the comet will be 8th magnitude and visible in many smaller backyard telescopes and even binoculars from dark sites. Christensen should remain bright enough to see in modest sized backyard telescopes for all of 2009.

On the morning of April 21, I was able to observe this comet with both 30×125 binoculars and a 12″ dobsonian. The comet was much easier to see in the 12″. Observation was made under a moderately light polluted sky with a limiting mag of ~+5.5.

A finder chart for Comet Christensen can be found at Comet Chasing.

A nice collection of images can be found at the VdS-Fachgruppe Kometen (Comet Section of Germany) and Seiichi Yoshida’s Comet Homepage.

Asteroids

Binocular and Small Telescope Asteroids (V < 10.0)

(1) Ceres

Ceres is the biggest asteroid in the Main Belt with a diameter of 585 miles or 975 km. It is so big that it is now considered a Dwarf Planet. Classified as a carbonaceous (carbon-rich) Cg-type asteroid, there are suggestions that it may be rich in volatile material such as water. Some even propose that an ocean exists below its surface. Ceres is one of two targets for NASA’s Dawn spacecraft which is scheduled to visit it in 2015. Last month Ceres was at opposition (at its closest to the Earth and at its brightest). This month Ceres will fade from from magnitude 7.4 to 8.0 as it ends is retrograde motion just north of Leo. If you are observing Saturn with a telescope or pair of binoculars, try your hand at finding Ceres with one of the finder charts linked below.

A finder chart (needs to be flipped upside down for Northern Hemisphere observers) can be found at the Royal Astronomical Society of New Zealand. Finder chart for Ceres from Heavens Above.

(2) Pallas

Pallas is also a carbonaceous asteroid though with a slightly bluish B-type spectrum. Due to its high inclination (tilt of its orbit with respect to Earth’s orbit) of 34 degrees it is a difficult target for future spacecraft missions. Pallas is large with dimensions of 350×334x301 miles or 582×556x501 km. This month it continues moving north, leaving the constellation of Orion and entering Monoceros. It fades from  magnitude 8.7 to 8.9 over the course of the month.

A finder chart (needs to be flipped upside down for Northern Hemisphere observers) can be found at the Royal Astronomical Society of New Zealand. Finder chart for Pallas from Heavens Above.

(8) Flora

Flora is a large asteroid roughly 136×136x113 km in dimension. It is innermost large asteroid in the Main Belt. As a result, it can get bright enough for backyard observers with modest sized telescopes and binoculars. Flora is a stoney S-type asteroid and also the largest member of the Flora family. This family was created when a large impact occured on Flora. The other family members are pieces of Flora that were thrown off by the impact.

Flora starts the month at magnitude 10.0. It reaches its maximum brightness on April 22 at magnitude 9.8. By the end of the month, it has slightly faded to 9.9. Flora and Irene provide us with a 2-for since both objects are located within 5 degrees of each other.

Since there I have not been able to find a nice star chart showing the position of Flora, here is one I made with the C2A program. It also shows the position of Irene.

(14) Irene

Irene was discovered by John Russel Hind in 1851, being only the 14th asteroid known at the time (if you are wondering ~400,000 asteroids have been discovered to date, we’ve come a long way). It is an S-type asteroid with a stoney or silicate composition. Its takes 6.3 years to orbit the Sun.

This month Irene will brighten from magnitude 9.2 to a maximum of 8.9 on April 24 as it retrogrades through western Virgo. Remember Flora is located within 5 degrees of Irene.

(15) Eunomia

Discovered in 1851, Eunomia is one of the largest stoney S-type asteroids. Its dimensions are roughly 357×255×212 km. Similar to Flora, Eunomia is also the parent body of its own family.

Eunomia spends all of April in the constellation of Corvus, just to the south of Virgo. With opposition on April 2, the asteroid is as bright as it’s going to get this year at magnitude 9.8. As the month progresses it will fade to 10.0. This year Eunomia is at aphelion, its furthest from the Sun making this one of its faintest oppositions. When at perihelion, it can get as bright as magnitude ~8.

Since there I have not been able to find a nice star chart showing the position of Eunomia, here is one I made with the C2A program.

(29) Amphitrite

Discovered in 1854, Amphitrite was the 29th asteroid to be discovered. Similar to Euterpe, Amphitrite is also a stoney S-type asteroid. With an average diameter of  127 miles (212 km) it is bigger than Euterpe though its further distance from the Earth and Sun keeps it from getting as bright.

Amphitrite fades from magnitude 9.5 to 10.1 this month. It spends the entire month in eastern Virgo not far from Saturn. If you are observing Saturn, take a short star-hopping trip to Amphitrite

Since there I have not been able to find a nice star chart showing the position of Amphitrie, here is one I made with the C2A program.

Venus: -4 Days Till Inferior Conjunction

Venus is getting harder and harder to see as it approaches inferior conjunction with the Sun. Due to breezy conditions in Tucson and all of the dust it kicked up, I was unable to locate Venus Monday afternoon. Luckily Bob Lunsford had better luck. Below are 2 pictures he took with his Celestron 9.25″ SCT and a Canon PowerShot digital camera.

This afternoon I was successful in finding Venus. At the time of the last observation (Mar. 24.83 UT), Venus was only 9.7 degrees from the Sun. The disk of Venus is now 59″.1 arc seconds (almost a full arc minute) across but only 1.4% of it is illuminated by the Sun. The crescent of Venus appears thicker in my Mar. 24th images compared to some of the previous dates because the seeing (turbulence in the Earth’s atmosphere) was much worse today. I just could not get a clear shot.

Venus… -6 Days Till Inferior Conjunction

We are now within a week of Venus‘ inferior conjunction. From my backyard there is no way to observe Venus at night any more (too many trees on the horizon). As a result, all observations are during the day, usually late in the morning or late in the afternoon. The hardest part after finding Venus (I don’t have a computerized telescope so I need to find Venus in binoculars first) is trying to see Venus on the screen on my laptop in broad daylight.

As Venus marches (or orbits) towards inferior conjunction, it is gradually appearing larger and thinner. This is obvious to telescope users. Even small binocular users can easily see Venus as a crescent. For those with great eyesight, it may even be possible to see Venus as a crescent with just your eyes.

Below is a direct comparison between Venus from today and 2 weeks ago. On Mar. 8.06 UT, Venus was 0.332 AU from Earth (30.8 million miles or 49.4 million km). It was 50″.2 arc seconds in diameter and 12.6 percent of its Earth-facing disk was illuminated by the Sun. At the time, it was also easy to observe being 28.7 degrees from the Sun.

Today at Mar. 21.73 UT, Venus was 0.286 AU from Earth (26.6 million miles or 42.6 million km). The closer distance means Venus is now 58″.3 arc seconds across (or 16% bigger). As can be seen below, much less of the disk is illuminated (2.4%). The observation is also much tougher now that Venus is only 12.7 degrees from the Sun.

At its closest to the Earth on March 27, Venus will be 0.281 AU from Earth (26.1 million miles or 41.8 million km). Only 0.97% of its 59″.3 arc second Earth-facing disk will be illuminated by the Sun. Hopefully at that time Venus will appear as a ring when its atmosphere refracts sunlight around its edge.

Saturn and Venus

The evening sky is graced by two planets, brilliant Venus low in the western sky and Saturn in the eastern sky. As nice as these planets look to the eye, telescopes can reveal even more about these worlds.

Saturn has 61 satellites (moons) with good orbits. It undoubtedly has many more and if we count every particle in its rings the count would probably be in the millions. Most of the 61 known satellites are very small (a few miles in diameter) and only observable in large telescopes or by the Cassini spacecraft that is currently orbiting Saturn.

Luckily a few satellites are observable in small backyard telescopes. Titan, the 2nd largest satellite in the solar system, is even visible in binoculars. Through my backyard 12″ telescope I can usually see 6 satellites. Imaging can pick up a few more. Images from the night of March 15/16 found 7 satellites in the close vicinity of Saturn.

The below image is a combination of two different exposure times, very short exposures to see the rings and cloud bands of Saturn and longer exposures to detect the moons. The detected moons include Enceladus, Tethys, Dione, Rhea, Titan, Hyperion and Iapetus.

Venus continues to drop closer to the Sun every evening. As it comes closer to Earth and moves between the Sun and Earth, Venus is becoming larger and more narrow. The below collage documents the apparent changes in our view of Venus over the past 9 days.

A more dramatic display of the changes over the past 9 days can be seen when images from March 8 and 17 are placed next to each other. The camera and telescope used is the same for each night. The magnification used is also the same. The change in size and thickness of the crescent is due to Venus moving closer to Earth.

Venus Closes in on Conjunction

Venus continues to drop closer to the horizon every evening. After reaching its furthest angular distance from the Sun (known as Greatest Elongation) on January 14  at a distance of 47 degrees, Venus has cut that distance by more than half (now at 22 degrees) as the planet approaches the Sun by ~1 degree per day. This all sets the stage for Inferior Conjunction on March 27 when Venus will be located only 8 degrees from the Sun. As close as that sounds, can appear even closer to the Sun and, in fact, can appear to pass in front of, or transit, the Sun. The last transit was in June of 2004, the next one will be on June 5-6 in 2012. After that we have a long wait until 2117.

For the past few days, I’ve been observing Venus from my backyard. Due to all the trees around my home, I can no longer get a clear shot of Venus after sunset. Luckily, Venus is bright enough that with some effort it can be located during the day when the Sun is still up. The sequence of 5 images shown below are of Venus on March 8, 10, 11, 12 and 13 UT. The first 4 images were taken an hour or less before sunset while the last image was taken around noon.

Notice that Venus is getting thinner with time. This is especially evident when you compare the 1st and last image (March 8 and 13). Also Venus is slowly growing in size as it comes closer to Earth.

I will try to observe Venus up to and after Inferior Conjunction. But considering how hard it is to get images of Venus now, I’ll consider myself very lucky to be able to see anything in a weeks time.

For more info on Venus and this month’s conjunction with the Sun, see my blog entry from a few days ago: “Venus Approaching Inferior Conunction“.

Venus Approaching Inferior Conjunction

Based on a number of comments to this blog, many people have noticed Venus. Shining high in the evening sky over the past few months, Venus is the brightest thing in the sky after the Sun and Moon. All this is rapidly changing. Those of you who have been watching Venus night after night have probably already noticed that it is not as high in the sky as it was a month ago. Careful observers may also have noticed that Venus is not as bright as well (though still much brighter than any other planet or star).

Venus’ reign over the evening sky is about to end. Over the next few weeks, Venus will be seen lower and lower in the sky. By the end of the month, it will no longer be visible as Venus shifts to the morning sky.

So what’s going on?

Being the 2nd planet from the Sun, Venus orbits inside the orbit of Earth. Like a race car passing on the inside of a turn, Venus is passing the Earth as they orbit the Sun. On March 27, Venus catches up with the Earth and passes between the Earth and Sun, an event known as “inferior conjunction“.

Relative positions of Venus and Earth on Mar 1, Mar 27, and May 1. Produced with the C2A program.

Orbit diagram showing the phases of Venus. Modified from an image by Ville Koistinen via Wikipedia Commons.

Just like the Moon, Venus displays different phases. It was these changing phases that Galileo observed ~400 years ago and convinced him that Venus was orbiting the Sun rather than the Earth. When it is located on the other side of the Sun, we see a small Venus with a near-full phase. As Venus comes closer to Earth, its phase becomes gibbous (between half and full), then half and finally it appears as a crescent. The whole time Venus increases in size  it comes closer to Earth. Its crescent shape is because as it approaches inferior conjunction, we view more and more of its nightside. After inferior conjunction, Venus vaults into the morning sky and the progression of phases reverses (crescent to half to gibbous to full) while its distance from Earth increases. An example of Venus’ changing phases can be seen in the collection of images taken by Statis Kalyvas of Thessalonica, Greece in2004.

Phases of Venus taken by Statis Kalyvas of Thessalonica, Greece in 2004. Image from the European Southern Observatory via Wikipedia Commons.

The changes are obvious in images taken with my 12″ telescope over the past ~10 days. In that time, the distance to Venus has decreased by 16% meaning Venus appears 16% larger (from 43″ to 50″ in diameter). The percentage of its disk illuminated by the Sun has also decreased from 22% to 13%.

At inferior conjunction on the 27th, Venus will be almost an arc minute in diameter (59″) but only 1% illuminated. On that date, Venus will be a difficult observation since it will be located only 8 degrees from the Sun. Observers with an unobstructed view of the western and eastern horizons may be able to catch a view of Venus both in the evening and morning sky. At that time, a telescope would see Venus as a ring like the bottom right photo in the images above from 2004. What we are seeing, is the light from the Sun passing through the atmosphere of Venus.

In The Sky This Month – March 2009

This feature highlights a number of meteor showers, comets and asteroids which are visible during the month of March 2009. This month sees the end to Venus’ reign over the evening sky. Also Comet Lulin should continue to be bright enough for easy evening observation.

Note: If anyone has pictures or observations of these objects/events and want to share them, send me a comment. I’ll post them here.

Planets

Venus has been putting on quite a display for the past few months in the evening sky. Unfortunately, the show comes to an end this month. At the beginning of the month, Venus is still riding high in the western sky after sunset. As the month progresses, it will appear lower and lower in the sky. Most people will have a hard time seeing it by mid-month. On March 27, Venus will pass between closest to the Sun. After that date, it will become a morning object. Early hour risers will witness Venus in all of its glory for most of the rest of the year.

This month Saturn will at opposition. The exact date being March 8. Opposition is when a planet (or comet or asteroid) is located opposite the direction of the Sun. On this date, Saturn will be closest to Earth and at its brightest. It rises at sunset and by 9pm is high enough to be easily seen. Even at its brightest, Saturn is not as brilliant as Venus or Jupiter. Still at magnitude +0.5, it is brighter than all but the 9 or 10 brightest stars.

The evening sky for March 15 at 9:45 pm. Chart produced with the Stellarium planetarium program.

This opposition is actually one of Saturn’s dimmest. The reason is that the rings of Saturn contribute a lot  to the brightness of Saturn. But this year, is a ring plane crossing year meaning that the rings are nearly edge-on. As a result, the rings are reflecting much less light in the Earth’s direction this year.

Jupiter and Mars are located near each other low in the early morning sky. As the month progresses Jupiter will become easier and easier to see. At magnitude -2.1, Jupiter is brighter than any star in the sky.  Mars on the other hand will only be visible to those with a clear view of the southeastern horizon. At magnitude 1.2, Mars would just crack the Top 20 in brightest stars in the sky.

Early morning sky right before dawn on March 15. (produced with Stellarium)

Mercury is still visible low in the east just before dawn. Due to the angle of the ecliptic with the morning eastern horizon this month, Mercury is a very difficult object to observe from the Northern Hemisphere but an easy object from the Southern Hemisphere. It will be lost to Northern observers a few days into the month. Southern observers will be able to follow it till a bit past mid-month.

Meteors

The month of March experiences no major showers and only a few minor ones. It continues the annual lull in meteor activity from mid-January to mid-April.

Sporadic Meteors

Sporadic meteors are not part of any known meteor shower. They represent the background flux of meteors. Except for the few days per year when a major shower is active, most meteors that are observed are Sporadics. This is especially true for meteors observed during the evening. During November, six (6) or so Sporadic meteors can be observed per hour from a dark moonless sky.

Major Meteor Showers

None.

Minor Meteor Showers

Minor showers produce so few meteors that they are hard to notice above the background of regular meteors.

Delta Leonids (DLE)

The Delta Leonids are another minor shower with a period of activity from February 15 to March 10. Near its February 25 peak, rates may reach a paltry 2 per hour.

Gamma Normids (GNO)

This shower is best from the Southern Hemisphere since it radiates from the southern constellation of Norma. Observers north of +40 deg North will not be able to see any GNOs. Then again it is such a minor shower that there is doubt whether it even exists!

The shower spans from Feb 25 to March 22 with a peak around March 13 with a maximum ZHR of 4.

Additional information on these showers and other minor showers not included here can be found at the following sites: Robert Lunsford’s Meteor Activity Outlook, Wayne Hally’s and Mark Davis’s NAMN Notes, and the International Meteor Organization’s 2008 Meteor Shower Calendar.

Comets

Naked Eye Comets (V < 6.0)

Comet Lulin starts the month as a barely naked eye comet at magnitude 5. More on this comet can be found in the next section.

Binocular Comets (V < 8.0)

Comet C/2007 N3 (Lulin)

Comet Lulin was discovered by the Lulin Sky Survey in Taiwan on 2007 July 11. At the time the comet was located beyond the orbit of Jupiter. The comet will be closest to the Sun on 2009 January 10 at 1.21 AU from the Sun. It will be closest to Earth in late-February when it will be only 0.41 AU from us.

The comet is currently around magnitude 5.2 which makes it an easy object for binoculars and small telescopes from a dark sky. From a dark rural moon-less sky, it can even be seen with the naked eye. Over the course of the month, the comet will fade from naked eye view but still be bright enough for binocs/small telescopes. By the end of the month, Lulin will be close to 7th magnitude.

After a few months as a morning object, Lulin spends all of March visible in the evening. Due to its retrograde orbit, the comet is moving in almost the exact opposite direction as the Earth. As a result, it is rapidly moving to the west every night. Over the course of the month, Lulin will start the month in western Leo, cross Cancer and end in the middle of Gemini.

A finder chart for Comet Lulin can be found at Comet Chasing.

A nice collection of images can be found at the VdS-Fachgruppe Kometen (Comet Section of Germany) and Seiichi Yoshida’s Comet Homepage.

Small Telescope Comets (V < 10.0)

Comet C/2006 W3 (Christensen)

This comet was discovered over 2 years ago on 2006 November 18 by Eric Christensen of the Catalina Sky Survey north of Tucson. At the time the comet was located at 8.7 AU from the Sun which is nearly the distance of Saturn. The comet continues to move closer to the Sun and Earth and is currently 3.8 AU from the Sun and 3.4 AU from the Earth.

The comet is currently around magnitude 9.7 and will slowly brighten during the month.  It is moving near the border of Lacerta and Pegasus.  The comet is best seen in the early morning. I was able to observe the comet visually with my backyard 12″ reflecting telescope in November. Being small and condensed, the comet was fairly easy to see.

The comet will continue to brighten as it approaches perihelion at a still rather distant 3.12 AU from the Sun on 2009 July 6. At that time, the comet will be 8th magnitude and visible in many smaller backyard telescopes and even binoculars from dark sites. Christensen should remain bright enough to see in modest sized backyard telescopes for all of 2009.

A finder chart for Comet Christensen can be found at Comet Chasing.

A nice collection of images can be found at the VdS-Fachgruppe Kometen (Comet Section of Germany) and Seiichi Yoshida’s Comet Homepage.

Comet 144P/Kushida

Comet Kushida was discovered by Japanese amateur astronomer Yoshio Kushida back on 1994 January 8. With an orbital period of 7.6 years, this year marks its 3rd appearance since discovery.

The comet was not expected to get brighter than magnitude 10 or 11 but recently observers have estimated it is as bright as magnitude 9.1. With perihelion this January 26 at 1.44 AU from the Sun, the comet should start to rapidly fade. The comet starts the month near the border of Taurus and Orion before moving across the “club” of Orion and into Gemini.

A finder chart for Comet Kushida can be found at Comet Chasing.

A nice collection of images can be found at the VdS-Fachgruppe Kometen (Comet Section of Germany) and Seiichi Yoshida’s Comet Homepage.

Asteroids

Binocular and Small Telescope Asteroids (V < 10.0)

(1) Ceres

Ceres is the biggest asteroid in the Main Belt with a diameter of 585 miles or 975 km. It is so big that it is now considered a Dwarf Planet. Classified as a carbonaceous (carbon-rich) Cg-type asteroid, there are suggestions that it may be rich in volatile material such as water. Some even propose that an ocean exists below its surface. Ceres is one of two targets for NASA’s Dawn spacecraft which is scheduled to visit it in 2015. Last month Ceres was at opposition (at its closest to the Earth and at its brightest). This month Ceres will fade from from magnitude 6.9 to 7.4 as it moves into Leo Minor, just north of Leo. If you are observing Saturn with a telescope or pair of binoculars, try your hand at finding Ceres with one of the finder charts linked below.

A finder chart (needs to be flipped upside down for Northern Hemisphere observers) can be found at the Royal Astronomical Society of New Zealand. Finder chart for Ceres from Heavens Above.

(2) Pallas

Pallas is also a carbonaceous asteroid though with a slightly bluish B-type spectrum. Due to its high inclination (tilt of its orbit with respect to Earth’s orbit) of 34 degrees it is a difficult target for future spacecraft missions. Pallas is large with dimensions of 350×334x301 miles or 582×556x501 km. This month it continues moving north, leaving the constellation of Lepus and entering southern Orion. It fades from  magnitude 8.4 to 8.7 over the course of the month.

A finder chart (needs to be flipped upside down for Northern Hemisphere observers) can be found at the Royal Astronomical Society of New Zealand. Finder chart for Pallas from Heavens Above.

(4) Vesta

Though not as large as Ceres, Vesta is more reflective making it the brightest asteroid in the Main Belt. Vesta is peculiar in that it appears to have evidence of volcanism on its surface. Similar to the Moon, Vesta may be covered with large expanses of frozen lava flows. It is classified as a V-type asteroid and is the only large asteroid with this classification. Many of the smaller V-type asteroids are chips of Vesta blasted off it by past asteroid and comet impacts. Vesta is similar in size to Pallas with dimensions of 347×336x275 miles or 578×560×458 km. Vesta will also be visited by NASA’s Dawn spacecraft which will arrive in 2010. On October 30, Vesta was at opposition (directly opposite from the Sun in the sky) and at its brightest. This month Vesta is an evening object moving through Aries before entering Taurus near the end of the month. It will fade from magnitude 8.3 to 8.5.

A finder chart (needs to be flipped upside down for Northern Hemisphere observers) can be found at the Royal Astronomical Society of New Zealand. Finder chart for Vesta from Heavens Above.

(14) Irene

Irene was discovered by John Russel Hind in 1851, being only the 14th asteroid known at the time (if you are wondering ~400,000 asteroids have been discovered to date, we’ve come a long way). It is an S-type asteroid with a stoney or silicate composition. Its takes 6.3 years to orbit the Sun.

This month Irene will brighten from magnitude 9.9 to 9.2 as it travels through Virgo. Next month it will reach its brightest on April 21 at magnitude 8.9.

(27) Euterpe

Euterpe was the 27th asteroid discovered when it was first seen in 1853. It is an S-type asteroid with a stoney or silicate composition. With a diameter of 58 miles (96 km) it is much smaller than Ceres, Pallas or Vesta. The reason it can get as bright as them is due to its orbit which brings it closer to the Sun and Earth. This month Euterpe will be roughly 1 AU from Earth and 2 AU from the Sun.

This month Euterpe is located in Cancer not far to the east of the Beehive Star Cluster. It starts the month at magnitude 9.7 and fades to 10.5 making this an object for advanced observers.

A finder chart (needs to be flipped upside down for Northern Hemisphere observers) can be found at the Royal Astronomical Society of New Zealand. Finder chart for Euterpe from Heavens Above.

(29) Amphitrite

Discovered in 1854, Amphitrite was the 29th asteroid to be discovered. Similar to Euterpe, Amphitrite is also a stoney S-type asteroid. With an average diameter of  127 miles (212 km) it is bigger than Euterpe though its further distance from the Earth and Sun keeps it from getting as bright.

Ampitrite reaches it brightest for the year on March 22 at magnitude 9.1. It starts the month at mag 9.7, brightens to 9.1 at opposition and fades back to 9.4 at month’s end. It spends the entire month in Virgo.

Venus and Sirius – 2 Bright Stars in the Evening Sky

First a meteor update: The weather continues to be bad for meteor observing in both Tucson and San Diego. Though my camera has been able to pick up a meteor or two per night between the clouds, daily updates don’t make for very exciting reading.

There have been quite a few comments on this site regarding one or two bright stars that are visible every night in the evening. The two stars in question are Venus and Sirius.

By far the brightest “star” in the sky during the evening hours is Venus. Though to the eye it looks like a star, Venus is actually the 2nd planet from the Sun. For the next few weeks Venus is at its brightest and highest in the sky. This combination makes it the most obvious object in the sky after the Sun and Moon.

Venus appear as a brilliant yellow star many times brighter than any other star in the sky. It is ~18 times brighter than the brightest star Sirius (located in the southeast) and ~75 times brighter than Capella (the bright star located nearly over head in the evening). It is so bright in fact, that it can be fairly easy to see in broad daylight if one knows exactly where to look. Located 40 degrees above the southwest horizon at sunset, it sets below the horizon around 9 pm.

Why is Venus so bright? It is due to a combination of factors. Venus is covered in a permanent shroud of highly reflective clouds. These clouds reflect ~65% of the sunlight that hits it. For comparison, the Earth reflects ~35% and Mars and the Moon around 13-15% of the sunlight striking them. Venus is also rather large, being only a bit smaller than the Earth (its radius is ~95% as large as Earth’s). The final piece of Venus‘ brightness puzzle is its close distance to Earth. Right now Venus is 0.494 AU (~46 million miles) from Earth. By comparison Saturn, the other bright planet visible in the sky, is 8.50 AU (~790 million miles away). Only Mars can get as close though it can never get as bright because it is smaller and less reflective than Venus.

Through a telescope or pair of good binoculars Venus appears like a miniature crescent Moon (see the image below). Over the next month and a half, Venus will appear larger and larger. It’s crescent shape will also become more narrow. If I can get my telescope and camera system to work properly, I will try to post some Venus images over the next few weeks.

Predicted telescopic view of Venus for February 10, 2009. Image from the NASA JPL Solar System Simulator. (http://space.jpl.nasa.gov/)

The 2nd bright “star” in the evening sky is Sirius. Sirius is the brightest star visible in the night sky with only Venus, Jupiter, and sometimes Mars being brighter. By the time it gets dark, Sirius is visible low in the southeast. It is visible for most of the night in the southern sky.

Sirius is a blue star but can appear to change color rapidly. The reason for this is due to the Earth’s atmosphere. Turbulence in the atmosphere causes the star’s light to be “bounced” all over the place. The light of the star is made up of many different colors which all “bounce” around differently. As a result, normally blue Sirius can appear to rapidly switch between many different colors when it is close to the horizon (meaning its light is passing through more atmosphere than usual). All stars experience this effect, it is just that Sirius‘ brightness makes it more evident. Watching Sirius when low in the sky with a telescope or just your eyes can be one of the best sights in the night sky.

Why does Sirius twinkle and change colors while much brighter Venus does not? Check out Phil Plait’s explanation on his Bad Astronomy site.

More on Sirius can be found here.