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Roy Tucker prepares for nightfall with one of several backyard telescopes, a 14-inch Celestron. (Courtesy Roy Tucker)

How to discover asteroids in your spare time

Roy Tucker has the answer.

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By day, Roy Tucker is a senior engineer at the Imaging Technology Laboratory at the University of Arizona. But at night he tracks asteroids—which he has found by the hundreds. Tucker is the foremost American amateur discoverer of Near-Earth Asteroids (NEAs), with a total of six discoveries, and one shared object, the famous (99942) Apophis. A&S Associate Editor Rebecca Maksel talked with Tucker about his work in December 2010.

Air & Space: How many asteroids have you discovered to date?

Roy Tucker: [I’m credited with] 467 numbered objects as of December 3, 2010. But I’m not doing so much asteroid observing now. The professional surveys have become so good that basically all I’m seeing nowadays are known objects. Up until about a year ago, I was still able to make some main-belt asteroid discoveries and such. [But now] my discoveries have fallen essentially to zero. The period of amateur discovery is drawing to a close. Some are still doing well, mostly with larger telescopes, but it’s time for me to find something else to do.

I got started observing asteroids—as far as measuring positions and looking for near-earth objects—late in 1996. And at that time, it was a wide-open field. It was possible to look pretty much anywhere in the sky and find new asteroids. [I would set] my telescope and camera in what’s called scan-mode imaging, in which I turn off the telescope drive and allow the rotation of the earth to cause the sky to slowly scan through the field of view. The camera operated in such a way that it was sort of like a cosmic fax machine, producing a long strip image of the sky.

By this means I was able to find all the moving objects in a strip of sky several degrees long. I noted which ones were old known-objects that had been known for years and years; which ones were brand new discoveries, the ones I was credited with discovering at that time; and those that had been recently discovered by other folks—it was quite impressive. In one strip of sky, I think I was [credited] with 10 main-belt asteroid discoveries. So the field was just totally wide open at that time. I was pretty well acquainted with the folks who operate the LINEAR [Lincoln Near-Earth Asteroid Research] survey, and although they cover lots of sky, I could go a bit fainter. So we coexisted quite well.

But LINEAR began to really take a great bite out of the population of unknown, undiscovered objects. They discovered hundreds of thousands of new asteroids, and really began to add to the total of known objects that the Minor Planet Center was keeping track of.

And then the Catalina Sky Survey folks here at the University of Arizona began to operate. I must confess it’s a bittersweet thing, because working at the University of Arizona CCD Laboratories here, I actually helped engineer the CCDs [charge-coupling devices] that they use for their surveys. It’s sort of like I shot myself in the foot providing them with the CCDs! But I know the folks there, and I’m really happy that they’re doing great things with the devices we’ve provided them. But nevertheless, they’re the ones who really put me out of business. They cover huge amounts of sky; they go really faint, and it got to where I couldn’t find anything that they hadn’t already found.

Astronomy is a big field, and I’m moving on to other things, variable stars and such, and I’m having a lot of fun going into the variable star field. All of the images that I acquired during my asteroid search period were archived, and I’m collaborating with professional astronomers, extracting the variable stars from the photometry from those images, and from each two-year survey, we get something like 26,000 new variable star candidates. So that’s enough to keep me quite busy, right there! So although I will say that I had a lot of fun discovering near-earth asteroids, that field has been pretty much worked out by the professional surveys now. And I’m glad they’re doing it.

As far as worrying about the impact threat, there’s no doubt that we should worry about it. Discoveries of the asteroidal near-earth objects has proceeded to the point where most of the really threatening objects are known, but the long-period comets [those with a period longer than 200 years] constitute nearly half of the impact threat. And by the nature of their orbits, it’s really difficult to discover these objects when they’re far from the sun.

A&S: When you talk about transferring over to the study of variable stars, what sort of information are you looking for?

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