Comets, Asteroids and Supernovae
Harry Colvin
Finding astronomical objects can present both novice and experienced observers with real challenges. On one end of the scale are the Messier objects. Relatively easy to find, they are bright and their locations are well documented on printed charts and reference texts. What is really nice is that they stay in one place, relative to the outline of the proximate constellations and reference stars. More difficult are the Herschel objects. They are harder to locate because of their magnitudes, many in the range of 11 to 13. But even these objects stay put, and knowing where and how to locate them is simply a matter of learning your equipment, having dark sky conditions, and practicing the art of star-hopping with printed or computer generated charts.
Comet Machholz on January 10, 2005. Image stack of twenty 10 second images taken with LX200 at f6.3 with MX916 camera. Image enhanced to bring out the short tail corona detail with DDP filtering. Image taken by Harry Colvin from a private observatory on Bainbridge Island, WA.
Of course one can always “cheat” by using a GO TO mount. I have found that for some objects, cheating is almost a necessary evil. Dim comets and almost all asteroids are extremely difficult to locate and confirm, even when one uses GO TO methods. I am not referring to bright comets like Machholz, which was naked-eye visible by some for over a month in late December and January. But try to find, as I did one night about a year ago, a small magnitude 11 comet using charts. No way does this work for me.
I recently started an asteroid observing program with the eventual goal of some day making a discovery. But first, as I found out, I had to learn how to find documented asteroids in the range of Magnitude 10to 12. Even this was not easy, because asteroids look like stars and many, unlike man-made satellites, do not move across the sky very fast. But by using telescope control software such as that in Starry Night or Cartesdu Ciel, I am able to place my LX200 10” within five arc minutes of the asteroid’s location and “on” my CCDchip. I can then obtain images with my MX 916 CCDcamera, and using the Internet, download DSS images to determine which “star” is in fact the asteroid. Isn’ttechnology great!
Star field image stack including asteroid 58 Elpis. Images taken at ca 9:30 p.m. Image by Harry Colvin.
Another method of detecting asteroids is the use of“blinking” software to find objects that are moving relative to background stars. Clyde W. Tombaugh used the blinking method at Lowell Observatory in 1930 to find the asteroid (some would say planet) Pluto, without the assistance of computer software, of course. By using a series of three asteroid images taken over period of time and performing plate reductions one can also calculate the asteroid’s orbit and predict where the asteroid will be in the future.
To discover and report newly discovered asteroids that you can name, you must pass a test to determine if you and your equipment can perform asteroid imaging and plate reductions with precision. The Minor Planet Committee will then issue your observatory a number and you can officially play the asteroid discovery, orbit prediction, and naming game. All this is in fact serious business, because as we know asteroids have impacted earth in the past and will again in the future. Once you have an observatory number, you are in effect competing in the asteroid discovery game with well funded and large robotic telescopes that scan the sky looking for NEO’s (Near Earth Objects). This means if an amateur wants to discover an asteroid, he or she should image in places in the sky where the robots don’t scan, and should seek dim small rocks with magnitudes in the range of 18 to 20.This is a test. Can you spot the asteroid 58 Elpis using the two images below? I took these image stacks on the night of January 17 about one hour apart. It’s not easy without blinking software so, if you can’t spot the asteroid, see the illustration at the end of the article for the answer.
I should point out that you really don’t need a CCD camera to find and confirm an asteroid observation. You need only average observational skills and patience. Once you are fairly certain that you are looking in the correct part of the sky, simply sketch the star field through your eyepiece, then return several hours later and re-sketch the same star field. Then compare the two sketches to determine what has moved.
Star field with the Mag. 10.9 star TYC 2911-01538-1 circled. Autoguided image stack of ten 120 second images taken with an LX200 at f 6.3 with a MX916 CCD camera. Image taken at ca 8:30 p.m. on February 8, 2005 from a private observatory on Bainbridge Island WA. Images were stacked and preprocessed with flat fields, dark frames and filtered using DDP. Image by Harry Colvin.
Star field image stack taken at ca 10:30 p.m. showing asteroid 58 Elpis circled. Image by Harry Colvin.
Another fun thing one can do with asteroids is observe an occultation; i.e., the eclipsing of a star by an asteroid. The effect of an occultation is that the eclipsed star blinks off for one–three seconds. It is a strange phenomenon to behold. By noting the duration of the blink and the exact time and location of your observation in combination with other astronomers’observations, the asteroid’s size, shape, and other information can be determined. The International Occultation Timing Association forecasts these events. In the Pacific Northwest, we had an opportunity to observe just such an event on February eighth. The asteroid 709 Fringilla was going to occult a 10.9 star. I was all set up with the clock on the PC synced with Internet time signals. I had located and confirmed the star that was going to blink. By comparing DSS images with those I had imaged I was certain I was looking at TYC 2911-01538-1. My plan was to remove my camera around 11:00 p.m. and replace it with a 12 mm eyepiece to observe the event. And to get the correct timing of the event I was going to start a sound file at exactly11:06 p.m. and record my observations by voice. The occultation was to occur around 11:08 p.m. But it was not to be and yes, you guessed it, clouds moved in around 10 p.m. preventing the observation. There is one class of object more difficult to observe than asteroids and dim comets. That’s a supernova event, the result of an exploding star in a galaxy faraway. Supernova discoveries take on average about 5,000 hours of search time per discovery. Most of these discoveries are made with robotic telescopes that mine the sky while their owners are sleeping. I don’t have one of these so I will not be playing this game. Once a supernova event is discovered and reported, the big telescopes all over the world study the event. Then the object fades away over several days and all one is left with is a number and a location recorded in a computer database somewhere. Sorry, but I don’t have any images of supernova objects, at least none that I have taken.