Comet PANSTARRS is putting on a nice show in the evening sky. Even though it is located low in the west and is definitely affected by the brightness of the twilight sky, many observers have been able to spot it with the naked eye and small binoculars. My magnitude estimates place the comet around magnitude +1.5. This agrees with estimates made by other observers from around the world.
Here in Tucson, I first saw the comet on Sunday night. Though I first spotted it in 10×50 binoculars I was able to see it, with difficulty, with the naked eye. On Tuesday and Wednesday evening, the comet was much easier to see. Here in Tucson we are blessed with dry, clear skies so I the comet was relatively easy to spot with the naked eye.
On Tuesday night, a thin crescent Moon was located only a few degrees to the right of the comet. Salvador Aguirre of Hermosillo, Sonora, Mexico imaged the pair. His image comes very close to matching what the comet and Moon looked like to the naked eye. Note that the comet really only looks like a faint star with a hint of a tail. And this is under dry clear Sonoran skies. Anyone observing from locations with any amount of humidity and/or smog will have a much harder time to see the comet. This is why binoculars are a must for finding and enjoying the comet.
The following image was taken on the same night as Salvador’s by Bob Lunsford from Chula Vista, CA. This view closely matches what the comet looks like in small binoculars.
The view of the comet gets better in a telescope. Salvador also acquired a movie of the comet as it set through his telescope.
I was able to get a few images of the comet through my 12″ dobsonian. Unfortunately the telescope doesn’t have a tracking mount so I had to obtain a hundred or so very short exposures and co-add them.
The comet is slowly moving higher in the sky every night. This should make the comet easier to see though the comet will also start to fade as it moves away from the Sun. Also the Moon will start to become a problem as it gets brighter. For those who want to observe the comet please see Bob King’s finder charts at his Astro Bon blog.
This evening I was successful in visually seeing Comet C/2011 L4 (PANSTARRS) for the first time. Though not an easy object to see I was consistently able to observe it with the naked eye after ~7:00 pm when the comet had already descended to an elevation of ~4-6 degrees above the horizon.
The comet was much easier to see in 10×50 and 30×125 binoculars. Though the comet appeared as nothing more than a faint star to the unaided eye, its yellow color and 0.3-0.4 degree long tail were very obvious in the binoculars.
Due to the bright sky and lack of bright stars near the comet it was difficult to estimate the brightness of the comet. Using a few stars that were much higher in the sky and atmospheric extinction tables produced by Dan Green at the International Comet Quarterly, I estimated the comet to be magnitude +1.5.
Now that I’ve seen the comet, I can recommend that anyone attempting to see the comet for themselves needs the following: 1) a very clear horizon free of any obstructions, 2) binoculars and 3) plan your observations in advance to pinpoint exactly where the comet will be in the sky. For #3 I noted the point on the horizon where the Sun set and then determined that the comet would be located near the same azimuth of the location of sunset. Then it was just a matter of time (over 30 minutes after sunset) till the sky darkened enough for the comet to appear.
Bob King has a nice collection of finder charts that will help in locating the comet over the next few weeks. Finding the comet will be a little easier on Tuesday evening because a very thin crescent Moon will be located only a few degrees to the right of the comet.
Today (March 10) at 4 hours UT (or GMT) comet C/2011 L4 (PANSTARRS) reached perihelion, or the point in its orbit when it is closest to the Sun. The time of perihelion passage corresponds with 9 pm on the night of March 9 for Tucson (MST -7 hours). At that time PANSTARRS was located at a distance of 0.302 AU from the Sun (28.0 million miles or 45.1 million km) which is ~3.3 times closer to the Sun than the Earth’s average distance and about 1 million km closer to the Sun than Mercury gets. On March 5 it also came as close to the Earth as it will get, a rather distant 1.097 AU (102.0 million miles or 164.1 million km). This is 10% further than the distance between the Earth and Sun.
As the comet rounds the Sun it is quickly heading north. After months of being only visible from south of the Equator, those of us up north will have the comet to ourselves starting this week. Already observers as far north as New Jersey (latitude 40°) have reported seeing the comet. Here in Tucson I tried to find the comet last week but it was still too deep in the bright twilight to see. Now that a recent bout of rain and clouds has moved through I will try again this evening.
The video below by Jay Lawson from Sparks, Nevada (latitude 39.5°) shows what the comet looks like in a small telescope or pair of binoculars (note the video is in black and white so it doesn’t show the true color of the comet and sky).
Another video from Brisbane, Australia back on Feb. 23 gives a good idea of what the comet will look like to naked eye observers. Please note that even though the comet is a very bright magnitude 1.5 and this does place it among some of the brighter comets of the past, it is not an easy object to see. If it were located high up in the night sky it would be unmistakable with a tail many degrees long to the naked eye. Such a well placed comet would even be visible under bright city lights. But Comet PANSTARRS is not located up high in a dark sky but rather close to the horizon against a bright twilight sky. By the time the sky is dark the comet will either have set or will be only a few degrees above the horizon.
Bob King has a great post about PANSTARRS on his blog Astro Bob. He highlights one of the problems of spotting a comet so close to the horizon, especially one in the western sky near the just set Sun. Many reports of PANSTARRS have actually been of distant aircraft contrails. His posting shows the different appearances of the comet versus plane contrails.
Comet C/2011 L4 (PANSTARRS) has been thrilling observers in the southern hemisphere for the past few weeks as it approaches its March 10 perihelion at a distance of 0.30 AU from the Sun. Over the next week, the comet will travel north and become visible (though still a difficult sight) for those of us north of the Equator.
At discovery PANSTARRS appeared to be an intrinsically bright comet and many forecast that it would brighten to magnitude -1 or so. But as is common for dynamically new comets making their first trip through the inner Solar System, PANSTARRS’ rate of brightening slowed down. With the comet as close to the Sun and Earth as it will get it should not brighten further. Still at magnitude +1.5 it ranks as one of the brighter comets of recent times.
The image below shows PANSTARRS in at its current best. The image is interesting in that it shows us a lot about this particular comet. First off, it is a brilliant yellow. Being a dust-rich comet, the dust it has released does a very good job of reflecting the light of the Sun, hence the yellow color. Its yellowness is also enhanced by the excitation of sodium atoms in the comet’s dust. This is especially true for comets that have perihelia at small heliocentric distances.
The other thing to notice in the image below is that PANSTARRS has three separate tails. The most obvious is the broad dust tail extending towards 11:30am position from the head of the comet. This tail is composed of dust released by the comet over the past few weeks. The narrower dust tail extending towards the 9:30 am direction is composed of larger dust particles that were released by the comet over the past few years. It is very possible that some of this larger dust may even have been released before the comet was discovered when it was located 10-20 AU from the Sun and activity was driven by highly volatile ices. The third tail is the hardest to see. It is easiest seen near the top of the image as a thin long tail just to the right of the main dust tail. This faint thin tail is the comet’s gas or ion tail. Its faintness is a clear indication that PANSTARRS is not a very gas-rich comet. Note, that the gas tail is usually bluish in color so it is not as easy to see in a bright (and blue) twilight sky compared to the yellow dust tails.
Though observers down under have had the comet all to themselves the past few months, PANSTARRS is now rapidly moving north. Last night I tried to spot the comet during bright twilight with 10×50 binoculars here in Tucson with no luck (latitude 32°). Also Salvador Aguirre was unsuccessful in his naked eye attempts to spot the comet from Hermosillo, Mexico (latitude 29°). The northernmost observations that I know of is from Malaysia (as reported by Spaceweather.com) (latitude 5°).
The lack of northern observations should change rapidly. Luckily for us, the Moon will be well placed to point the way to the comet next week. On the evening of March 12, the comet will be located within 2 to 3° to the left of the Moon. Even then this will be a very difficult observation. A clear unobstructed view of the west horizon is a must as the two will be only a few degrees above the horizon. Also binoculars are highly recommended as even the Moon will be very difficult to find due to its thinness, faintness, low elevation and the brightness of the sky.
Over the next few weeks the comet will slowly appear higher in the sky though it may not be till early to mid-April till we see a nice view of the comet in a dark sky. By that time the comet will have faded to a faint naked eye object (for folks under dark skies, city folks will likely have to rely on binoculars to spot the comet by then). The finder chart below was produced by Bob King (‘Astro Bob’).
As impressive as the comet appeared in the first image above, to the naked eye it should look more like the image below.
Comet Pons-Gambart may be the center of attention in the comet community lately, but it is not the only comet putting on a show. This morning is was able to observe Comet C/2012 K5 (LINEAR) at magnitude 9.6. In 30×125 binoculars, the comet was nicely condensed with a coma 3′ across and a tail 5′ long. The comet is currently located near the end of the Big Dipper’s handle in Ursa Major.
Right now the comet is located 1.16 AU from the Sun 0.66 AU from Earth. Having passed perihelion on Nov 28 at 1.14 AU the comet is now heading away from the Sun. But it is still heading towards Earth and will pass within 0.29 AU (27 million miles or 43 million km) of us on Dec 31. It will brighten all month as it closes in and should be around magnitude 8.0 by month’s end.
C/2012 K5 (LINEAR) is a long-period comet discovered by the LINEAR near-Earth asteroid survey program on May 25, 2012. At the time the comet was around magnitude 17-18. Though it passed through perihelion on Nov. 28 at a distance of 1.14 AU, the comet will become brighter this month as it rapidly approaches the Earth. Close approach will occur at the very end of December at a distance of 0.29 AU (27 million miles or 44 million km).
Recent visual observations place the comet around magnitude 10.0 at the end of November. The comet should brighten by another 2 magnitudes by the end of December. This month it is primarily a northern hemisphere object and spends much of the month running the length of the Big Dipper from the handle to the bowl before rocketing southward through the rest of Ursa Major into Lynx. The fact that it spends the first 3 weeks of the month among the familiar stars of the Big Dipper should aid many people in seeing the comet.
The comet starts the month as a small telescope object but by the middle of the month it should be visible in binoculars for observers under a dark sky. For bright sky observers a small telescope may still be needed.
I did observe the comet back on Oct. 21 with the University of Arizona’s Kuiper 1.5-m telescope. Though still over a month from perihelion and located low in the sky, the comet displayed an impressive tail and even some near-nucleus jet activity.
Comet C/2012 V4 (which is mostly likely a return of Comet Pons-Gambart) was discovered on images taken by the solar observatory spacecraft SOHO (though the SWAN instrument used for the discovery watches the entire sky not just the region near the Sun). But SOHO isn’t the only spacecraft watching the vicinity of the Sun. The comet is currently crossing the field of the HI2 instrument on the STEREO-B spacecraft. Thanks to Marco for posting a link to a YouTube video showing the comet in the STEREO images.
The comet is first visible on images from November 21 and then rapidly brightens and develops a long thin tail by the time of the last high-resolution data from STEREO on December 6. The distance between the comet and STEREO is rapidly decreasing from ~0.9 AU on the 21st to ~0.4 AU on the 6th. The distance will continue to drop to a minimum of 0.28 AU on December 12. This means Pons-Gambart will get much closer to STEREO-B and, as a result, much brighter than seen from Earth. As you can see in the plot of the inner Solar System to the right, STEREO-B is located along the Earth’s orbit but trailing the Earth by 120° or 1/3rd of the way around the Sun.
I downloaded images taken by STEREO-B from their public website and created a movie showing the motion and brightening of C/2012 V4. The comet is very difficult to see at first but becomes much easier to notice halfway through the movie.
The single image below has been annotated to show the direction of motion of the comet as well as the outline of some of the more prominent constellations in the field like Orion, Taurus and Auriga. Also the Earth and Jupiter are also in the field. The Sun is located just off to the left of center. After the comet passes near the Sun it will pop back into view again except this time in the FOV of the HI1 camera which images the space on the other side of the Sun.
Last night I estimated the brightness of C/2012 V4 at magnitude 9.4 from my backyard. At that time the comet was 0.84 AU from the Sun, 1.54 AU from Earth and 0.32 AU from STEREO-B. The phase angle (Sun-Comet-Observer angle) from Earth was 35° and 131° from STEREO-B. Correcting for the difference in distances and phase angles means magnitude 9.4 from Earth translates to a magnitude of [9.4 – 3.4 (due to distance) – 0.8 (due to phase angle)] = ~5.2 from STEREO-B.
Note, the movie above was created from differenced images. In order to pull out more details on the solar wind one image is subtracted from another. That is why the image shows each star and even the comet as positive-negative pairs. The solar wind is the wispy material seen blowing from the left to right.
Last evening (Dec. 7 UT) the sky was finally free of cirrus and I was able to see newly discovered comet C/2012 V4, the first probable return of Comet Pons-Gambart since 1827. This evening (Dec. 8.06 UT) I was able to spot the comet again using Mars as a guide since the two bodies are within a few degrees of each other.
In short, this was a very difficult comet to observer. It was invisible in my 30×125 binoculars and I could only see it with averted vision in a 12″ dobsonian. Though the sky is relatively dark at my house (Milky Way always visible and LM of ~+6.0), the comet was located within 10° of the horizons and in the direction of the skyglow from Tucson. I estimated a brightness of 9.4 and a coma 1′.5 across. If C/2012 V4 were located overhead it wouldn’t have been a problem. For example, 168P which was also around magnitude 9.4 in early October was visible in 10×50 binoculars but it was much higher and located away from city lights.
Unless the comet undergoes a rapid brightening soon it will only get harder to observe as its elongation slowly decreases.