In The Sky This Month – May 2011

This feature highlights a number of meteor showers, comets and asteroids which are visible during the month of May 2011.

May 2011 Highlights
* Venus, Jupiter, Mercury and Mars gather low in the dawn sky
* Saturn is easy to spot in the evening
* Eta Aquariids put on a night display for southern observers

Note: If anyone has pictures or observations of these objects/events and want to share them with my readers, send them to the Transient Sky at <transientsky1@yahoo.com>.

Planets

Moon - The table below lists important lunar dates for the month, including the phases of the Moon and nights of lunar-planetary and lunar-stellar conjunctions.

May 1 - Moon 7° from Mercury, 6° from Jupiter and 5° from Mars
May 3 - New Moon
May 5 - Moon 7° from bright star Aldebaran
May 8 - Moon 9° from bright star Pollux
May 9 - Moon 5° from Beehive Cluster
May 10 - First Quarter Moon
May 11 - Moon 5° from bright star Regulus
May 14 - Moon 8° from Saturn
May 15 - Moon 3° from bright star Spica
May 17 - Full Moon
May 18 - Moon 3° from bright star Antares
May 24 - Third Quarter Moon
May 29 - Moon 5° from Jupiter
May 30 - Moon 4° from Mars
May 31 - Moon 4° from Venus

Saturn – Saturn is now a month past opposition. As a result, the ringed planet is still near its brightest for the year (currently magnitude +0.5 to +0.7) and is also visible throughout the evening and most of the morning hours. Saturn is a slow moving planet and takes 29 years to circle the Sun as well as 29 years to do one circuit around the ecliptic constellations. As has been the case all year long, Saturn is still located in Virgo about 13-14° from 1st magnitude Spica.

May 14 - Saturn and Moon 8° apart

Venus, Mercury, Mars and Jupiter -  The planetary show of the year is a series of compact groupings involving Venus, Mercury, Mars and Jupiter. Unfortunately, all the action will take place very close to the eastern horizon in a bright dawn sky for northern observers. South of the equator the view will be much easier to see.

From May 7 to 15, Venus, Mercury and Jupiter will be within 5° of each other. On May 11, the trio will be within ~2° of each other. A similar trio of Venus, Mercury and Mars will be within 5° of each other from May 15-25 with their tightest grouping of ~2° on May 21.

May 1 - Moon 7° from Mercury, 6° from Jupiter and 5° from Mars
May 1 - Jupiter and Mars within 0.4° of each other
May 6 - Mercury at greatest elongation west
May 7 - Mercury and Venus within 1.4° of each other
May 11 - Venus, Mercury and Jupiter within 2.1° of each other
May 18 - Mercury and Venus, again, within 1.4° of each other
May 21 - Venus, Mars and Mercury within 2.1° of each other
May 23 - Venus and Mars within 1° of each other
May 29 - Moon 5° from Jupiter
May 30 - Moon 4° from Mars
May 31 - Moon 4° from Venus

Meteors

Meteor activity is near a seasonal minimum in May. The year is usually split in 2 with January through June having low rates with few major showers while July through December 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 May mornings, 10-12 or so Sporadic meteors can be observed per hour from a dark moonless sky.

Major Meteor Showers

Eta Aquariids (ETA)

The Eta Aquariids are a major shower, especially for southern hemisphere observers, when they peak on May 6. 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. As a result the ETA radiant is only visible for an hour or so before twilight. This year the Moon is near New so the sky will be dark.

The shower spans from April 19 to May 28 with a peak around May 5 with a maximum ZHR of ~60. The poor placement of the radiant for northern observers will greatly limit the number of observed meteors.

Minor Meteor Showers

Minor showers produce so few meteors that they are hard to notice above the background of regular meteors. Starting this month, info on most of the minor showers will be provided on a weekly basis by Robert Lunsford’s Meteor Activity Outlook.

Additional information on these showers and other minor showers not included here can be found at the following sites: Wayne Hally’s and Mark Davis’s NAMN Notes, and the International Meteor Organization’s 2011 Meteor Shower Calendar.

Comets

Naked Eye Comets (V < 6.0)

None this month…

Binocular Comets (V = 6.0 – 8.0)

None this month…

Small Telescope Comets (V = 8.0 – 10.0)

C/2011 C1 (McNaught)

It seems like every year sees a bright Comet McNaught and this year is no different. The 58th comet discovery by Rob McNaught and 74th from Siding Spring Observatory, C/2011 C1 was first seen on February 10th of this year. Though intrinsically faint, the comet is currently being reported as bright as magnitude 9.0. CCD images taken by the author on Apr 1 UT confirm that the comet was between magnitude 9.0 and 9.5 at that time (see image below). Unfortunately the comet should fade this month as it passed perihelion on April 17 at a distance of 0.88 AU from the Sun. The comet starts May 0.92 AU from the Sun and 1.23 AU from Earth. These distances will have increased to 1.02 AU from the Sun and 1.39 AU from Earth by mid-month and 1.17 AU from the Sun and 1.52 AU from Earth at the end of the May.  Comet C/2011 C1 is a morning object low in the east and travels from Pegasus to Pisces this month.

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Asteroids

Binocular and Small Telescope Asteroids (V < 8.0)

(4) Vesta

Vesta is the brightest asteroid in the Main Belt. This is due to its high albedo (or reflectivity) which causes it to reflect ~42% of the light that strikes it. Vesta is also 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 has dimensions of 347x336x275 miles or 578×560×458 km.

The maps below were created from images taken with the Hubble Space Telescope. The geography is dominated by a large impact crater located near the south pole (the blue ‘donut’ in the elevation map). Perhaps this crater is the result of the impact that blasted off the smaller V-type asteroids. We’ll know more this summer when NASA’s Dawn spacecraft enters orbit around Vesta for a full year. Currently the encounter is scheduled for July 2011 to July 2012.

Images and models of the shape of asteroid (4) Vesta. In the upper left is a real HST image, to the upper right is a model of Vesta’s shape, and on the bottom is an elevation map . Credit: NASA/STScI.

Vesta spends the month around magnitude 7.3 to 6.9 as it moves eastwards through western Capricornus. Opposition is on August 4 at magnitude 5.6.

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.

In The Sky This Month – April 2011

This feature highlights a number of meteor showers, comets and asteroids which are visible during the month of April 2011.

April 2011 Highlights
* Saturn is the only easily visible planet
* The rest of the naked eye planets congregate in the morning sky at the end of the mont

Note: If anyone has pictures or observations of these objects/events and want to share them with my readers, send them to the Transient Sky at <transientsky1@yahoo.com>.

Planets

Moon - The table below lists important lunar dates for the month, including the phases of the Moon and nights of lunar-planetary and lunar-stellar conjunctions.

Apr 3 - New Moon
Apr 7 - Moon 2° from Pleiades
Apr 8 - Moon 7° from bright star Aldebaran
Apr 11 - First Quarter Moon 9° from bright star Pollux
Apr 12 - Moon 5° from Beehive Cluster
Apr 14 - Moon 5° from bright star Regulus
Apr 17 - Moon 8° from Saturn and 2.5° from bright star Spica
Apr 18 - Full Moon
Apr 20 - Moon 3° from bright star Antares
Apr 25 - Third Quarter Moon
Apr 30 - Moon 6.6° from Venus

Saturn – This month Saturn is at opposition. As a result, the ringed planet is at its brightest for the year (magnitude +0.4) and is also visible all night long though it is best around midnight. At the start of the month Saturn may be too low in the SE at dusk to be easily seen but by month’s end it is far enough off the horizon at dusk to be easily seen. Saturn is a slow moving planet and takes 29 years to circle the Sun as well as 29 years to do one circuit around the ecliptic constellations. As has been the case all year long, Saturn is still located in Virgo about 11-13° from 1st magnitude Spica.

Apr 3 - Saturn at Opposition
Apr 17 - Saturn and Moon 8° apart

Venus, Mercury, Mars and Jupiter -  The long slow grind towards superior conjunction continues. This month Venus rises only an hour or so before the Sun and never gets very high in the ESE to E sky. Though Venus is a difficult sight for northern observers it is worth searching out at the end of April. During the last week of the month (and into May) Venus will be visited by 3 planets in the best planetary alignment of the year. Starting around the 25th, Mercury peaks above the eastern horizon 40 minutes before sunrise. Over the next few nights, Mars and Jupiter join the show. Use the crescent Moon on the 29th and 30th to point the way.

Apr 30 - Moon 6.6° from Venus

Meteors

Meteor activity is near a seasonal minimum in April. The year is usually split in 2 with January through June having low rates with few major showers while July through December 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 April mornings, 10-12 or so Sporadic meteors can be observed per hour from a dark moonless sky.

Major Meteor Showers

Lyrids (LYR)

The Lyrids are usually good for 10-20 meteors per hour under a dark sky. This month the just past Full Moon will make the shower difficult to observe. So these remnants of Comet Thatcher will probably go unobserved except by automated video systems and only the most dedicated of visual observers.

Minor Meteor Showers

Minor showers produce so few meteors that they are hard to notice above the background of regular meteors. Starting this month, info on most of the minor showers will be provided on a weekly basis by Robert Lunsford’s Meteor Activity Outlook.

Additional information on these showers and other minor showers not included here can be found at the following sites: Wayne Hally’s and Mark Davis’s NAMN Notes, and the International Meteor Organization’s 2011 Meteor Shower Calendar.

Comets

Naked Eye Comets (V < 6.0)

None this month…

Binocular Comets (V = 6.0 – 8.0)

None this month…

Small Telescope Comets (V = 8.0 – 10.0)

C/2011 C1 (McNaught)

It seems the past couple of years have seen a bright Comet McNaught and this year is no different. The 58th comet discovery by Rob McNaught and 74th from Siding Spring Observatory, C/2011 C1 was first seen on February 10th of this year. Though intrinsically faint, the comet is currently being reported as bright as magnitude 9.0. CCD images taken by the author on Apr 1 UT confirm that the comet is between magnitude 9.0 and 9.5 at this time (see image below). Unfortunately this will probably be as bright as the comet gets as it passes perihelion on April 17 at a distance of 0.88 AU from the Sun. It is also slowly moving away from Earth with a geocentric distance of 0.95, 1.06 and 1.22 AU from Earth at the star, middle and end of the month. Comet C/2011 C1 travels the length of Aquarius before ending the month near the Pisces/Pegasus border.

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Asteroids

Binocular and Small Telescope Asteroids (V < 8.0)

(4) Vesta

Vesta is the brightest asteroid in the Main Belt. This is due to its high albedo (or reflectivity) which causes it to reflect ~42% of the light that strikes it. Vesta is also 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 has dimensions of 347x336x275 miles or 578×560×458 km.

The maps below were created from images taken with the Hubble Space Telescope. The geography is dominated by a large impact crater located near the south pole (the blue ‘donut’ in the elevation map). Perhaps this crater is the result of the impact that blasted off the smaller V-type asteroids. We’ll know more this summer when NASA’s Dawn spacecraft enters orbit around Vesta for a full year. Currently the encounter is scheduled for July 2011 to July 2012.

Images and models of the shape of asteroid (4) Vesta. In the upper left is a real HST image, to the upper right is a model of Vesta’s shape, and on the bottom is an elevation map . Credit: NASA/STScI.

Vesta spends the month around magnitude 7.6 to 7.3 as it moves eastwards through western Capricornus.

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.

In the Sky This Month – July 2010

This feature highlights a number of meteor showers, comets and asteroids which are visible during the month of July 2010.

July 2010 Highlights

* Total Solar Eclipse on the 11th for the South Pacific
* Venus, Mars and Saturn close in on each other in the evening sky
* Venus passes within 2° of bright star Regulus on the 8th
* Mars and Saturn within 1.8° of each other on the 30th
* Mercury has a mediocre evening apparition in July/August (great from SH)
* Mercury passes within 0.3° of Regulus on the 27th
* Comet 10P/Tempel 2 reaches small telescope brightness in the morning sky

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

Planets

Venus – Venus is the brightest “star” visible in the early evening (at magnitude -4.2). Low in the west it sets about 2 hours after the Sun. Maximum height above the horizon was reached over a month ago. As a result, Venus will appear to sink lower in the sky every night. Still, it will be well placed for easy observing for the next 2 months. If you are located south of the equator, this is a great apparition and Venus will continue to climb higher till late August. Regardless, of where you are located it will be hard to miss brilliant -4 magnitude Venus in the west an hour or 2 after sunset.

July 10 - Venus within 1.0° of bright star Regulus
July 14 - Moon passes within 5.5° of Venus

Mars – Mars moves rapidly from the constellation of Leo and into Virgo this month. Though fading from magnitude +1.3 to +1.5 it is still an obvious red beacon in the southwest right after sundown. It’s brightness is comparable to that of the other bright stars. Mars starts the month 23° from Venus and 15° from Saturn. By the end of the month, Mars will have caught up to Saturn. Venus isn’t far behind and all three planets will share the same part of the sky in August.

July 16 - Moon passes within 5.6° of Mars
July 30 - Mars and Saturn within 1.8° of each other

Saturn – This month Saturn is located in Virgo and visible in the southwest during the early evening hours. At magnitude +1.1 it is slightly brighter than Mars. The two will be within 2° of each other at the end of the month. Telescope users should note that Saturn’s rings are still within a few degrees of edge-on.

July 16 - Moon passes within 7.4° of Saturn
July 30 - Saturn and Mars within 1.8° of each other

Jupiter - Jupiter once again returns to sight as a brilliant star in the east-southeast before dawn. The magnitude -2.6 planet will get brighter and better place for observing over the next few months. Last year Jupiter made a series of close approaches to Neptune. This year Jupiter will do the same for Uranus. All month long Jupiter will be located within 2-3° of Uranus.

July 3 - Moon passes within 6.5° of Jupiter
July 31 - Moon passes within 6.6° of Jupiter

Mercury - Mercury will start the month too close to the Sun for observation. By mid-month, it starts to peak above the western horizon after sundown.  The apparition is a great one for southern hemisphere observers but a so-so one for northern observers. The

July 12 - Moon passes within 3.9° of Mercury
July 27 - Mercury passes within 0.3° of bright star Regulus

Meteors

Meteor activity should really pick up in July. 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 JuLy, 10-16 or so Sporadic meteors can be observed per hour from a dark moonless sky.

Major Meteor Showers

No major showers are active this month.

Minor Meteor Showers

Minor showers produce so few meteors that they are hard to notice above the background of regular meteors. Starting this month, info on most of the minor showers will be provided on a weekly basis by Robert Lunsford’s Meteor Activity Outlook.

Additional information on these showers and other minor showers not included here can be found at the following sites: Wayne Hally’s and Mark Davis’s NAMN Notes, and the International Meteor Organization’s 2010 Meteor Shower Calendar.

Comets

Naked Eye Comets (V < 6.0)

None

Binocular Comets (V = 6.0 – 8.0)

None

Small Telescope Comets (V = 8.0 – 10.0)

Comet 10P/Tempel 2

’10P’ says it all. This was only the 10th comet to be observed at a 2nd apparition meaning we’ve been following this comet for a long time. Discovered by prolific German comet discoverer Ernst Wilhelm Leberecht Tempel in Marseille, France on July 4, 1873, Tempel 2 has been observed at nearly every return since then. The comet’s current orbit brings it to within 1.42 AU of the Sun on July 4 and to within 0.65 AU of Earth in late August.

The comet is currently at a brightness of 9.0 to 9.5 magnitude and should brighten by another half magnitude this month. This is a large diffuse object so it will be more difficult to see than your average 9th magnitude comet or deep sky object. From my moderately light polluted backyard and 12″ telescope, the comet was a difficult object and was estimated to be magnitude 10.0. From a dark site and 30×125 binoculars, the comet was much brighter (magnitude 9.5), larger and easier to see. The added brightness was probably due to the dark site allowing me to see much more of the comet’s coma.

Tempel 2 is a morning object moving from the constellation of Aquarius to Cetus.

A finder chart for Comet McNaught 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/2009 K5 (McNaught)

If you are looking for Comet C/2009 R1 (McNaught), which was a nice bright naked eye comet last month, this Comet McNaught isn’t the comet you’re looking for. C/2009 R1 is now too close to the Sun to be seen. The lesser known, and fainter but more observable, ‘Comet McNaught’  is Comet C/2009 K5 (McNaught). This will probably be the last month to catch a glimpse of this comet in backyard telescopes.

With perihelion back on April 30 of this year at a distance of 1.42 AU from the Sun, C/2009 K5 may still be bright enough to be seen in small backyard telescopes from dark sites. At mid-month it will be located 1.78 AU from the Sun and 2.47 AU from Earth.

Observations over the past month show the comet to be around magnitude 8.5. With the comet in full retreat from the Sun and Earth, it should fade rapidly from here on out. The comet will start the month between 8.5 and 9.0 but should fade to fainter than 10.0 by the end of the month. Due to its located in the northern constellations of Camelopardalis and Lynx, the comet can be seen at all hours of the night from high northern latitudes. It is best in the evening right after the end of twilight.

A finder chart for Comet McNaught 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 < 9.0)

(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 the other target of NASA’s Dawn spacecraft which is scheduled to visit it in 2015.

This month Ceres will be at opposition and brightest. The asteroid will start the month at magnitude 7.4 and fade to magnitude 8.1 by the end of the month. All month long it will be retrograding on the border of Sagittarius and Ophiuchus.

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.

“New” Comet Blues – Comet McNaught Falls Short

We should have known better. Early predictions called for Comet 2009 R1 (McNaught) to get as bright as 2nd magnitude. As recently as 2 weeks ago, I posted that it was on pace to reach magnitude 3.5 to 4.0. Now even that fainter magnitude was too bright. For the past 2+ weeks the comet has failed to brighten as seen from Earth. The plot below shows a fit (red line) to visual observations from early April to June 10. If the comet had continued to brighten at that rate it would be brighter than magnitude 4 by now. The blue curve is a fit to observations since June 10 and shows a comet that is at its peak and may even fade a little before reaching perihelion.

Apparent visual lightcurve for Comet C/2009 R1 (McNaught). Visual observations from the ICQ/CSC, COBS, CometObs. Created with Seiichi Yoshida's COMET program. Credit: Carl Hergenrother.

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How can the comet fade before reaching perihelion? The next plot shows how we can more accurately measure the brightness behavior of a comet. First the comets magnitude is normalized to a distance of 1 AU from Earth and to a phase angle of 0 degrees. Normalization to a geocentric distance of 1 AU is done by subtracting 5 log (Δ) from the magnitude, where Δ is the distance from Earth in AU at the time of the observations. Normalization to 0 degrees phase angle is done with Joseph Marcus’ function for dust scattering. I’m not going to go into any more detail on the Marcus function but interested readers will find it in the journal International Comet Quarterly, Vol. 29, No. 4.

The lightcurve shows a comet brightening at a normal and healthy rate until the comet reached a distance of 0.7-0.8 AU from the Sun. A brightening rate of 9.0 log r is in the ballpark for a long-period comet like McNaught. (Note, I discarded a few April observations from the fit because they seem to be a few magnitudes to faint. At this preliminary stage, their exclusion produces a more realistic fit to the April/May/early June data.) Sunward of ~0.7-0.8 AU the comet’s brightening slows considerable.

Heliocentric lightcurve for Comet C/2009 R1 (McNaught) normalized to 1 AU from Earth and o deg phase angle. Visual observations from the ICQ/CSC, COBS, CometObs. Credit: Carl Hergenrother.

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Another way to plot the data for McNaught suggests that the comet is producing less gas and dust and in an absolute sense has been fading for 2 weeks now. The below plot is not only normalized to 1 AU from the Earth and to o degrees phase angle but also to 1 AU from the Sun. In this case a 5 log (r) term is subtracted from the visual magnitude in addition to the 2 normalization terms mentioned above. An object that was releasing a constant amount of gas and dust would have a horizontal line with no slope on the plot, an object releasing more gas/dust as it approached the Sun would show a positive slope (line going up and to the right) while an object releasing less gas/dust would have a negative slope (line going down and to the right). For some reason Comet McNaught saw its gas/dust production start to decrease after reaching a distance of 0.7-0.8 AU from the Sun, or roughly around the date of June 10.

Heliocentric lightcurve for Comet C/2009 R1 (McNaught) normalized to 1 AU from Sun and Earth and o deg phase angle. Visual observations from the ICQ/CSC, COBS, CometObs. Credit: Carl Hergenrother.

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Extrapolating the latest brightness trends gives us a better idea of where the comet stands when compared to other comets that had perihelia of ~0.4 AU.

Peak absolute magnitude (near perihelion) of long-period and Halley-type comets. Credit: Carl Hergenrother.

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So what’s happening to Comet McNaught? The comet is a dynamically “new” comet. In layman’s terms the comet is on its first pass through the inner Solar System after spending the past 4.5 billion years in deep freeze in the outer reaches of the Solar System. We can tell this by its orbit which is nearly parabolic. The early brightness was due to very volatile ices which sublimate at low temperatures. These very volatile ices have now been depleted and the comet is relying on the usual assortment of cometary ices (water ice, carbon monoxide, etc.) to drive the creation of a coma and tail. So in a way, the comet faked us out by acting bigger and brighter than it really was.

“New” comets have been seen before and they have disappointed before. The most famous was Comet Kouhotek in 1973/74. Back in my early years of comet observing, C/1989 X1 (Austin) was predicted to be a bright comet. I even remember an issue of Sky and Telescope magazine with a cover tagline of “Monster Comet Coming”. As the lightcurve below shows, the comet brightened normally until it was about 1.2 AU from the Sun. After that the comet’s dust/gas production decreased even though perihelion was at a small distance of 0.35 AU. Rather than a brilliant naked eye comet, Austin was a 5th magnitude fuzzball even though it passed much closer to Earth than Comet McNaught ever will.

As for the future of Comet McNaught, it will poorly visible very close to the horizon for the next week or so. After that the comet will be forever invisible to northern observers. Perhaps observers in the southern hemisphere will get a shot at a rapidly fading McNaught in a few months. After that the comet will probably never be seen again. Its current orbit is hyperbolic which means the comet will be ejected from the Solar System never to return.

Heliocentric lightcurve for Comet C/1989 X1 (Austin). Visual observations from the ICQ. Credit: Carl Hergenrother.

Tonight’s Comet McNaught Finder Charts

The comet is still an easier (easier being a relative term) object to see in the morning sky. It also helps to live further north. In fact, it is impossible to see the comet south of the equator.

The comet is still in northern Auriga a few degrees to the east of the 0th magnitude star Capella. For observers requiring a better, fainter star chart, try this one.

Finder chart for finding Comet C/2009 R1 on the evening of June 26 and morning of June 24. Created with Stellarium.

Finding Comet McNaught Tonight (June 23/24)

Comet C/2009 R1 (McNaught) is still 2 weeks from perihelion (its closest approach to the Sun). Unfortunately it has become a difficult object to see as it is located very close to the northwest horizon in evening twilight and close to the northeast horizon in morning twilight. Also not helping is the fact that the comet’s brightening trend has stalled for the past 2 weeks at magnitude 5.0 to 5.5. More on that later today when I present another analysis of its lightcurve.

Last night I woke up early in the morning and attempted to observe the comet. Luckily for me the comet rose above the mountains right between 2 trees to the northeast of my house. Though visible in 10×50 binoculars, the comet was only slightly fuzzy and I probably would not have recognized it as a comet if I wasn’t already looking for it. At magnitude ~5.5 it might have been visible as a faint star to observers under very dark skies.

Below are rough finder charts for finding the comet this evening and morning. Though visible in the evening, the comet is easier (relatively) to see in the morning sky. Regardless of morning or evening, you will need an unobstructed view of the horizon. Also binoculars or a telescope will help. If you are lucky enough to live where it is very dark, then you might see if with just your eye. In that case the comet will appear as a faint star. In small binoculars, the comet will appear as a slightly fuzzy star (though under dark skies a tail may be visible). With larger binoculars or in a telescope the comet should be an obvious blue-green “fuzz ball” with a faint tail extending away from the horizon. Try using the bright 0th magnitude star Capella as a guide to where to find the comet. For observers requiring a better, fainter star chart, try this one.

Finder chart for finding Comet C/2009 R1 on the evening of June 23 and morning of June 24. Created with Stellarium.

The Latest on Comet McNaught

Comet 2009 R1 (McNaught) is the center of attention in the early dawn sky. The 5th magnitude comet is brightening as it plunges toward the Sun. Though not an impressive sight to the naked eye or in small binoculars, observers with large binoculars and telescopes (or dark skies) will be well rewarded.

I’ve been able to observe the comet a few times over the past few nights. On Monday morning I drove to the outskirts of Tucson to get a glimpse of the comet under dark skies. Though the sky is dark enough so the Milky Way is bright and distinct, the comet was just barely visible to the naked eye. Even then it appeared as nothing more than a faint star where one shouldn’t be. Based on that observation I put its brightness at magnitude +5.3.

In small 10×50 binoculars, the comet was a small fuzz not much bigger than the stars around it. The coma is only ~6 arc minutes across in the 10x50s so this is not a large comet. The gas tail was about a degree in length but was very faint and barely noticeable.

It took my giant 30×125 binoculars to really show the comet in all its glory. The coma (or head) of the comet was a brilliant blue-green. The color being due to the fluorescence of cyanogen (CN) and diatomic carbon (C2) in the comet’s atmosphere. The faint gas tail extended for over 2 degrees. Even a short 0.3 degree dust tail was visible. Interestingly this comet doesn’t show much yellow coloring which is the color of dust (really the color of the Sun reflecting off the dust). The lack of dust makes it a dust-poor or, conversely, a gas-rich comet.

The comet is currently 0.61 AU from the Sun and 1.14 AU from Earth. In 2 weeks it will be at perihelion and only 0.41 AU from the Sun though at a more distance 1.30 AU from Earth. There have been some published reports that the comet will become a brilliant object at 2nd magnitude. Unless there is an unexpected outburst the comet will not get that bright. Based on brightness measurements over the past few months, the comet is on track to peak at a magnitude of 3.5 to 4.0 (see figure below).

Unfortunately the comet will also be dropping closer and closer to the Sun. Even though 3rd magnitude is rather bright for a comet, its close location relative to the Sun will make it very difficult to observe. Most observers will be unable to observe the comet in another week or so, if not already. Even from my dark sky location, the mountains to the north of Tucson are already making it difficult to see the comet before the start of dawn.

Apparent magnitude estimates for Comet 2009 R1 (McNaught) up till June 15. Created with Seiichi Yoshida's COMET program. Credit: Carl Hergenrother.

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With a little more analysis we can determine if Comet 2009 R1 (McNaught) is a typically bright comet. The plot below shows the peak brightness near perihelion for comets with perihelion distances less than 1.5 AU. The brightness is not the apparent magnitude (how bright the comet looked to observers on Earth) but the heliocentric brightness (brightness of the comet normalized to 1 AU from the observer, 1 AU from the Sun and at a phase angle of zero degrees). This is done to “place” the comets at the same distance and orientation from the Sun and observer and allow a direct comparison between each comet. For example a candle a few feet from you looks much brighter than a distant star but it is the distance that makes it appear brighter. If both candle and star were located at the same distance the star would be many times brighter.

Since Comet McNaught is not yet at perihelion and we don’t know how bright it will be at that time, we plotted its brightness and orbital circumstances for June 14th. It is obvious that it’s a comet of just above average brightness for a comet at that distance from the Sun (the average heliocentric brightness is the blue line). Note that it is about 2 magnitude (6 times fainter) than Comet Halley. I also labeled Comet Hale-Bopp which is an obvious outlier on the plot and truly a once-in-a-lifetime comet.

Peak absolute magnitude (near perihelion) of long-period and Halley-type comets. Position of Comet 2009 R1 (McNaught) is valid for June 14. Credit: Carl Hergenrother.

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CCD observers have been producing some great images of the comet and its 2 tails. Check out Michael Jager’s website “Comet Pieces” for some of the best images out there.

Thanks to Gianluca Masi of Rome, Italy for sharing some images he took with a Celestron C14 at the Bellatrix Observatory in Ceccano, Italy. I was able to apply a radial gradient filter to bring out the fine detail. The image below shows a multitude of rays in the gas (ion) tail. These rays are very dynamic and can change on hourly time scales. Though there is some evidence of structure in the head of the comet, it is very subtle. This is too bad because well defined dust jets can be used to measure the rotation period of the nucleus and made out dust-producing active areas.

Image of Comet 2009 R1 (McNaught) taken on 2010 June 6.10 UT by Gianluca Masi with the Bellatrix Observatory Celestron C14. Radial gradient processing by C. Hergenrother. Credit: Gianluca Masi/Bellatrix Obseratory.

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