C/2013 US10 Catalina

Comet Catalina C/2013 US10 is currently visible in the Northern Hemisphere using binoculars or a small telescope. After rounding the Sun late in November, it has been up in the pre-dawn sky, creeping up higher each night.

It was observable in early December in New England, but very low in the sky before sunrise. I tried to get a look at it a few times using binoculars but was not able to see it well between the trees at home! Had hoped to see it later in December, but skies have been very cloudy and foggy for the past few weeks as part of a very unusually mild and damp weather pattern.

Having some time off recently, I thought I would try to see the comet using one of the internet telescope services available, and was able to get some images of it after signing up for a trial on slooh.com

After logging in and watching some of the getting started videos, I was able to book a timeslot (or “mission” as they call it) to see the Catalina comet on one of their telescopes in the Canary Islands . The site has a page titled “What’s Up” that gives a lot of great suggestions for currently observable objects to look at including planets, deep sky objects and visible comets. You simply select an available time, select the desired object you’d like to see and you are all set!

But for comets and other moving objects you need to determine the coordinates the target will be at and create a “Coordinate Mission” for that location of the sky. I used Stellarium to determine where Comet Catalina would be from the observatory location at the time of the reservation. Since the reservation times are in UTC, it is also handy to set the TimeZone plugin in Stellarium to work in that time zone. That way, you can check the position at a given time in UTC and not have to convert to your local time. (Or I guess you can change your workstation to UTC time and keep it there)! The coordinates calculated in Stellarium can be a bit off, so to get accurate positions expected from the coordinates of the actual observatory it’s good to use the MPC Minor Plan and Comet Ephemeris Service or the JPL Horizons site.

After you enter the coordinates, you select the type of object you are observing, so I selected the “bright comet” option. Apparently this setting determines the exposure time and image processing used for the session. The site appears to confirm that the coordinates are observable at the time selected and will even warn you if a fainter object is too close to the moon to be seen.

Once you set this all up, that’s it! You can stay on and watch the images from the telescope as they are taken. Since my reservation was around 1 AM local time, I just went to sleep while my images were being acquired!

The next day, I signed back into the site, selected the My Images page and found 4 images taken of the comet. The session used both a high magnification telescope (17″ CDK af f7) and a wide field APO refractor telescope. Images were taken at the same time, processed and made available as color and mono PNG files in the size of the original CCD images. These can be viewed on the site, downloaded, or annotated and emailed or shared to your favorite social media site.

Here is the high magnification image of C/2013 US 10 Catalina from this session on 30 Dec 2015:


It’s hard to see in the above version, but there is a faint tail extending up and right – I believe this is the dust tail. The ion tail extends a short ways down from the comet center. (North is up in this image).

I noticed several fuzzy objects around the comet. Not more comets, but apparently Catalina US10 was passing through an area with a few galaxies.

Slooh also provides FITS files from the CCD cameras. These are downloaded from the observatory at the end of each night and made available through the Slooh website and as well as an email notification.

So I was able to take the FITS file of the unfiltered or luminance image and reduce in Astrometrica. Then I could take estimated coordinates of each of the galaxies visible in the picture and check them against positions in TheSky. In the image above there are 5 clearly visible. I marked these in Astrometrica and they are shown in the image below, along with the fit and estimated location of the comets:


The dual tails are more clearly visible in the inverted image. I could also try stacking the color and luminance FITS files to see if I could bring these out better in the positive image. But I kind of prefer the above as it reminds me of working with AgBr imaging!

I took an image of the comet on the next night, and recently tried combining the FITS files to make my own LRGB composite using MaximDL. I need to better understand how to bring out the tails in that package but got a fairly good result:


The dust trail to the upper right appears to have a fork in it at this time – taken on 31 December.

The Catalina comet will continue to be visible through January and then fade as it moves away from the sun. Turns out this comet will not be back to greet us but will continue on outside of the solar system for parts unknown. Apparently is was a deep solar object that had its orbit perturbed enough to be knocked into an ejection trajectory that will take it outside of the Solar System.

Next, I will try capturing some of the other comets in the sky using Slooh and perhaps another similar service.





After getting back into astronomy recently, one new development I’m really enjoying is the great abundance of astronomical events, exploration and research on social media. Following progress, discoveries and images from the New Horizons mission in near real-time on Twitter, for example, has been a thrill and quite addicting!

But there has always been a fringe element around this subject, and that comes up in SM as well.Last month I saw some fear mongering about a major comet or asteroid due to hit the Earth in September, and subsequent rebuttal and denial by professionals. I don’t even want to post a link to the sites purporting this nonsense – but you could look it up! But it’s got me thinking about whether a really big celestial object could catch us by surprise..

I’ve also re-joined a local astronomy group and am looking forward to getting out with them again. Many of the members have changed, but they still have a core group of very dedicated observers. One of the former members I knew was a dedicated comet hunter, and would go out on many clear nights with a wide-field telescope or binoculars and scan the sky for fuzzy objects.

To hunt for comets by eye, you have to become acquainted with existing nebula, galaxies and other fuzzy objects. In fact, Messier developed his catalog for this very reason! He had identified over 100 objects (and these have been added to), and today there are a number of more comprehensive catalogs for all of the “fixed” deep sky objects visible in the sky.

The club also co-hosted a talk by Thomas Bopp a while back, who, of course, is one of the co-discoverers of the spectacular Hale-Bopp comet. He described stargazing with friends and noticing a faint fuzzy object he did not recognize. After checking start charts for known objects he suspected he had found a comet. After watching it for a while, he noticed movement, confirming that it was not a nebula or galaxy. He did not have a way to take a picture, so he sketched the comet relative to nearby stars and was able to work out a location for the new comet. Then he sent in the discovery the old-fashioned way – by telegram!

Alan Hale is an avid observer and hunter of comets and had also noticed the new visitor and sent in his observations as well. The comet was confirmed to be new and was named for the two co-discoverers.

When Hale and Bopp first viewed the comet, it was determined to be about 9 AU out from the sun or well over 1 million km from Earth. The comet was one of the largest and brightest seen in recent times and would surely cause major damage if it happened to hit the Earth, but how likely is that?

After a newly discovered comet or minor planet is observed for a few days, it’s quite straight forward to calculate it’s orbital path. The motion of any body in orbit around the Sun was determined by Kepler and others in the 16-17th centuries and explained by Newton. Any body captured by the Sun will travel in an ellipse – or a perfectly round circle which is a specific type of ellipse. The orbit of the planets is roughly circular for the most part, but long period comets like Hale Bopp move in a very elongated or eccentric track. Hale-Bopp makes a trip around the Sun every 2500 years or so and when it comes to visit it approaches 0.93 AU before traveling way out to the fringes of the Solar System at 370 AU. It’s thought that it used to go further out before it’s orbit was brought in a bit closer by Jupiter.

Given the orbital parameters for a comet, one can work out the probability for impact developed by Opik over 50 years ago and refined by scientists in the field since. The probability is determined by whether the orbits cross and how often, and the chance that both objects will be in the same place at the same time. This gets fairly complicated as the orbit of a comet or other smaller body is subject to precession as well as perturbation by other bodies. So the orbits can align from time to time increasing the chance of a crossing. But since there is lots of room out there and the visits infrequent, the collision probability from a long-period comet is estimated to be in the tens or hundreds of millions per year per potential impact.

Perhaps people imagine the probability of these collisions to be more likely than this very small number because of the pictures we’ve all seen of the Solar System. These are fine conceptually but impossible to draw at actual scale. As this page from the NOAO shows, if the Earth were represented as a small peppercorn, or about 1/10 of an inch across, it would be located about 25m from the Sun. And Hale Bopp would travel about 10,000 m away on every orbit, coming back every 2500 year for another shot. Another awesome, live scale model was made recently by Wylie Overstreet and Alex Gorosh in the Nevada desert and posted here.

So I don’t see how a big comet could take us by surprise, but we’ll soon see! Anyhow I’m still waiting for Planet-X to end us, which was another doomsday hoax propagated on Usenet a while back. Perhaps things have not changed so much after all..