Comet PANSTARRS now fading

Comet C/2011 L4 (PANSTARRS) peaked between magnitude +1.0 and +2.0 in the days after its March 10th perihelion. Since then the comet has moved away from the Sun and Earth is now located 0.57 AU from the Sun (versus 0.30 AU at perihelion) and 1.23 AU from Earth (versus 1.10 AU on March 5).

The comet is still a difficult object to observe since it located low in the northwestern sky during evening twilight. Adding to the difficulty is a nearly Full Moon and the fact that the comet has now faded to magnitude +3.0 to +3.5. That’s 4-6 times fainter than it was two weeks ago.

The image below was taken from my backyard near Tucson with a Canon 50mm F/1.4 lens, Hoya X1 (Green) filter and a Imaging Source DMK41 camera. It is a composite of 19 2-second exposures. As you can see by the trees, the comet was already quite low at an elevation of ~5 degrees above the horizon.

The image is also close to what the comet looked like in 7×50 binoculars. Close but not quite… I’d say the comet was looked a little fainter in the binoculars versus the image.

C2011L4_2013Mar24_50mm

Latest on Comet Pons-Gambart

I last reported on newly (re)-discovered comet C/2012 V4 back on December 8. Though comet C/2012 V4 has been linked with Comet Pons-Gambart which was last seen in 1827, it still has not been officially named Pons-Gambart.

Earthbound observers estimated it at magnitude 8.5 to 9.5 during the first half of December. Unfortunately the comet is now too close to the Sun to be seen from Earth. It won’t be seen again till sometime in mid to late January. How bright it’ll be at that time is debatable. There has been some talk on the comets-ml list that the comet continued to brighten after perihelion in 1827. If true and if the comet behaves the same way, the comet may still be bright enough at the end of January for small telescope observers.

As mentioned in my December 8 posting, one of the STEREO sun watching spacecraft has not only had a clear view of the comet but the comet passed within ~0.28 AU of the spacecraft on December 12. The movie below shows the comet rapidly brightening and displaying a lengthening tail as the comet zips past STEREO-B and off its camera FOV. Note that the tail on the last few frames almost extends from one edge of the field to the other. It is a clear reminder of how our view of a comet (faint and not much to get excited about from Earth while a naked eye object with a 20+ deg long tail from STEREO-B) is dependent on our viewing conditions.

C2012V2_STEREO_20121211

Wirtanen-id Meteors This Week?

This week sees the appearance of one of the years best meteor showers, the Geminids, this Thursday evening. But before the Geminids peak, there is a small chance that meteors from Jupiter-family comet 46P/Wirtanen may be visible over the next few nights. Note, we have never (at least not definitely) observed meteors from Wirtanen. But computer simulations of the trajectories of dust released by the comet suggest that the Earth may encounter dust from its 1927, 1934, 1941 and 1947 returns. It is uncertain if any meteors will be seen but as always, we’ll never know unless we look.

For those who’d rather wait for a more certain shower, the Geminids on Thu/Fri night will definitely put on a show. I’ll post more on that shower later in the week.

In the meantime, the excerpt below is from Bob Lunsford’s Meteor Activity Outlook for this week:

Meteors from comet 46P\Wirtanen? There is the possibility that we may be able to see meteor activity from comet 46P\Wirtanen as the Earth passes through several filaments of material produced when the comet passed through perihelion during the first half of the 20th century. This is strictly an evening display as any meteors from this source would have a radiant of 23:48 (357) +04. This position lies in western Pisces, just east of the circle of faint stars known as the “Circlet”. This area of the sky is best seen as it becomes dark as it culminates between 1800 and 1900 (6pm and 7pm) local standard time. The first of these encounters is with the material shed in 1947. The expected peak is at 06:21 Universal Time (UT) on December 11th. This corresponds to 22:21 (10:21pm) PST and 23:21 (11:21pm) MST on Monday evening December 10th. The radiant is too low for any activity to be seen in the eastern half of North America. The second encounter is material from 1941. This peak is expected to occur at 10:20 UT on December 12th. This is too late for North America but observers in Hawaii may be able to see some of this activity. The third encounter is produced from the 1934 return. This peak is expected to occur at 12:30 UT on December 13th. This timing favors the western Pacific area. The last possible encounter is produced by the 1927 return. This peak is expected to occur at 00:02 UT on December 14th. This corresponds to 19:02 (7:02pm) EST and 18:02 (6:02pm) CST on the evening of December 13th. This timing favors the eastern half of North America. If any meteors are produced from this source, they would be extremely slow.

Comet Hergenrother in Outburst

Fourteen years ago, a 25 year old version of myself stumbled across a faint new comet in the constellation of Aquarius. Circling the Sun every ~7 years, the comet is intrinsically faint and could be rightly considered a runt. This year the comet was perfectly placed with perihelion and opposition occurring within days of each other (perihelion on October 1). As a result this comet which only comes within 1.41 AU of the Sun is also passing within 0.42 AU of Earth. Based on its previous behavior it should have only brightened to 14-15th magnitude which is nothing special. Surprisingly it has experienced a series of outbursts and is now bright enough to be seen in small telescopes or even binoculars at magnitude 9.2 to 9.8.

Discovery images of Comet 168P/Hergenrother from Nov. 22, 1998. Credit: Catalina Sky Survey.

I’m probably one of the last people to write about the outburst of comet 168P/Hergenrother which is surprising since it’s one of my finds. It was discovered on images taken with the Catalina Schmidt (then a 0.41-m) telescope during the course of the Catalina Sky Survey (CSS). It was the 2nd of my four comet discoveries and my first CCD find [my first comet, C/1996 R1 (Hergenrother-Spahr) was found with photographic film]. Though I was the first to spot the comet the actual images were taken by either me, John Brownlee and/or Tim Spahr. Discovery images can be seen to the right. It’s not much to look at and the bad column sure didn’t help.

At that time, the CSS had just finished upgrading the Schmidt from a photographic instrument to a digital CCD equipped instrument. We still had a ways to go and didn’t even have automatic detection software yet. Instead we would take 3 images spaced about 10-15 minutes apart and difference (subtract one image from another after lining them up relative to field stars) 2 of the images. Objects that didn’t move such as stars would mostly disappear leaving a positive and negative spot for moving objects. We would then blink all three of the original images to make sure our suspects were real objects. It was highly inefficient but resulted in a few new near-Earth asteroid and comet discoveries before the automated detection system was available.

The 2012 return started routinely wit the comet brightening up to its expected 15th magnitude. The first sign of outburst activity was reported by J. J. Gonzalez (Spain) who visually sighted 168P at magnitude 11.2 on September 6. A second outburst must have occurred around the start of October. By October 3rd, observers such as Michael Mattiazzo (Australia) were reporting the comet at magnitude 9.8. Over the last few weeks brightness estimates have ranged between 9.2 and 10.0.

My own estimates are given below:

Oct. 11.10, 9.2, 6′ (C. W. Hergenrother, Tucson, Arizona, 30×125 binoculars);
Oct. 09.13, 9.6, 6′ (C. W. Hergenrother, Tucson, Arizona, 30×125 binoculars);
Oct. 08.19, 9.3, 3′ (C. W. Hergenrother, Tucson, Arizona, 30×125 binoculars);
Oct. 04.10, 9.8, 1.5′ (C. W. Hergenrother, Tucson, Arizona, 30×125 binoculars);
Oct. 04.10, 9.9, 2′ (C. W. Hergenrother, Tucson, Arizona, 0.31-m reflector).

The comet was easy in 30×125 binoculars from my backyard (LM = +5.7-6.0). Though the comet was visible in 10×50 binoculars it was hard to make an accurate brightness estimate due to the dense star field. My yard is fairly dark for a suburban site. If you live under brighter skies a larger telescope will be required to see the comet.

Since the start of its outbursts, the comet has looked relatively normal in CCD images with no sign of jets or secondary nuclei. Yesterday, Gianluca Masi (Italy) emailed me with images showing a ‘cloud’ of material tailward of the nucleus. Luckily I was scheduled on the University of Arizona’s Kuiper 1.5-m telescope and was able to confirm Gianluca’s observation. The image below shows the “cloud” trailing the nucleus in the anti-solar direction.

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So what’s happening? Luckily we saw something similar back in 2006 when comet 73P/Schwassmann-Wachmann 3 made a close approach to Earth. SW3 had undergone a splitting event back in 1995 which produced two major components (the original nucleus and a smaller secondary one). The smaller component (called 73P-B) was still experiencing outbursts and shedding material in 2006. From time to time, “clouds” of material would appear to drift back from the nucleus. High-resolution images showed this “cloud” to be composed of hundreds of small mini-comets, many probably no larger than a meter in size. As these mini-comets disintegrated they would produce short-lived mini-comae that lasted for only a day or so.

Look familiar?

Comet 73P-B (Schwasmann-Wachmann 3) as seen on 2006 Apr. 19.49 UT in Sloan i filter images taken with the Smithsonian Astrophysical Observatory SAO 1.2-meter on Mount Hopkins. Credit: Carl Hergenrother.

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Only a few weeks later the Hubble Space Telescope and ground-based telescopes such as the Vatican 1.8-m were able to resolve 73P-B’s “clouds” into a group of hundreds of mini-comets. More images of 73P-B taken with the SAO 1.2-m, Kuiper 1.5-m and VATT 1.8-m can be found here.

Image of comet 73P-B on 2006 May 1.3 UT with the Vatican 1.8-meter on Mount Graham. Credit: Carl Hergenrother.

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Could the same thing be happening with 168P? Possibly. Right now we aren’t sure what is exactly going on with 168P. The fact that the comet is experiencing outbursts means it is releasing a large amount of dust. It is very possible that it has also released a number of meter sized boulders. These boulders may be releasing dust causing the “cloud” visible trailing the main nucleus. Perhaps larger telescopes will provide better images over the coming weeks.

In the meantime, the comet is still visible to small telescope users as it moves northward from Pegasus to Andromeda. A finder chart can be found at Comet Chasing.

I can’t lie that I’ve had been waiting for this apparition of 168P and hoping it would become bright enough to be seen visually. As both an amateur and professional astronomer I still get a thrill seeing a comet with my own eyes. Having it be one of mine makes it even better. (Of my four discoveries, this is the 2nd I’ve been able to see visually. C/1996 R1 was 10th magnitude at discovery.) I look forward to seeing what other surprises 168P throws our way.

Good job, little 168P!

Comet 96P/Machholz Visible in SOHO Images

Updated (at 3 pm Tucson time on July 17).

Every ~5.3 years, comet 96P/Machholz makes a close and personal swing around the Sun. At a distance of 0.12 AU, comet Machholz comes within 11 million miles (18 million km). That is 8 times closer to the Sun than the Earth and even 2.5 times closer than the innermost planet Mercury.

Though the comet can become very bright at perihelion, its close proximity to the Sun makes it all but impossible to observe at that time. Luckily we have a number of spacecraft observing the Sun which can also be used to observe the comet. One such spacecraft, the joint ESA/NASA Solar and Heliospheric Observatory (SOHO) is currently picking up the comet. The image below is the latest image from the LASCO instruments on the spacecraft. [Update:  96P has now moved out of the SOHO LASCO field-of-view. As of 10 am (Tucson time) on the 13th, the comet is visible to the lower right of the Sun. A short tail is also visible trailing away from the Sun. As of 10 am (Tucson time) on the 14th, the comet is visible just to the upper right of the center obscuration. As of 10 am (Tucson time) on the 15th, the comet is visible halfway between the center and the top of the image. As of 8 am (Tucson time) on the 16th, 96P is visible near the edge of the field at the 11 o’clock position.  Since the comet is about as close to the Sun as it gets, it is also visible in the higher resolution LASCO C2 field. A real-time C2 image is located below under the C3 image. In the C2 image the comet can be seen near the upper right corner though it will move out of the field in a few hours. The comet is no longer visible in the C2 field.] Additional SOHO images can be found here.

Perihelion occurred on July 14.78 UT (or roughly 11:40 am Tucson time on the 14th, that’s 11:40 am PDT, 12:40 pm MDT, 1:40 pm CDT, 2:40 pm EDT). By the end of July, the comet will be visible in the evening sky as a faint and difficult 9-10th magnitude object for telescope observers.

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 – February 2011

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

February 2011 Highlights
* Jupiter rules the evening sky, while...
* Saturn becomes visible later in the evening...
* Venus continues to dominate the early morning sky.

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.

Feb 1 - Moon 3.5° from Mercury
Feb 3 - New Moon
Feb 7 - Moon 6° from Jupiter and Uranus
Feb 11 - First Quarter Moon
Feb 11 - Moon 1.4° from Pleiades
Feb 12 - Moon 7° from bright star Aldebaran
Feb 15 - Moon 9° from bright star Pollux
Feb 16 - Moon 4° from Beehive Cluster
Feb 18 - Full Moon 5° from bright star Regulus
Feb 21 - Moon 7.5° from Saturn and 2.6° from bright star Spica
Feb 24 - Third Quarter Moon
Feb 25 - Moon 3° from bright star Antares

Jupiter - The ‘King of the Planets’ continues its reign as the uncontested ‘King of the Evening Sky’ at magnitude -2.1. Located on the Pisces/Aquarius border, Jupiter is easy to find in the southwest as it gets dark.

Feb 7 - Moon 6° from Jupiter

Saturn – Saturn rises during the late hours of the evening. Located in Virgo, the ringed planet is a close match in brightness (mag +0.6) to Spica, the brightest star in Virgo (mag +1.0). Saturn spends the entire month within 8-9° of Spica.

Feb 21 - Moon 7.5° from Saturn

Venus – After passing through inferior conjunction in late October , Venus is now the dominant sight just before dawn. On Feb 1, Venus rises almost 3 hours before the Sun in the eastern sky though this drops to 2 hours over the course of the month. Unlike this year’s evening apparition which was poorly placed, Venus’ current stay in the morning sky will be a good one for northern observers. Through a telescope it currently looks like a brilliant ‘half moon’.

Mercury and Mars – Too close to the Sun for observation.

Meteors

Meteor activity is at a seasonal minimum in February. 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 February mornings, 10-12 or so Sporadic meteors can be observed per hour from a dark moonless sky.

Major Meteor Showers

None 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 this month…

Binocular Comets (V = 6.0 – 8.0)

None this month…

Small Telescope Comets (V = 8.0 – 10.0)

None

Asteroids

Binocular and Small Telescope Asteroids (V < 9.0)

(7) Iris

Iris is an inner Main-Belt asteroid that can occasionally get as bright as any asteroid. This year, Iris did not get as bright but was still become a binocular object at opposition on January 24 at magnitude 7.9. This month it is located in the constellation of Cancer a few degrees to the southwest of the Beehive Cluster. It starts the month at magnitude 8.1, but fades to 8.9 by the end of the month.

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.

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