In the Sky This Month – July 2009
July 4, 2009 88 Comments
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.
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.
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.
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.
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 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.
Naked Eye Comets (V < 6.0)
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.
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.
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.
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.
Binocular and Small Telescope Asteroids (V < 10.0)
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.
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.
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.