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?

Tucker: To give you an idea, one of the classes of objects that we are finding in our variable-star discoveries are what are called M-Dwarf Eclipsing Binaries. These are very small, lightweight stars.

Before our survey, there were only like six of these eclipsing binaries known, and we’ve added something like 30 from the first two-year survey. So, each of our two-year surveys—I’m working on the fifth one now—each one of these will yield something like 30 new eclipsing binary M-dwarf systems. That will give you an idea that even though the asteroid field is drying up, there are lots of other things that amateurs can do to productively contribute to the state of our astronomical knowledge.

This project, executed by both amateurs and professionals working together over a period of years with very little funding, has been enormously cost-effective compared to a purely professional effort in which a single night at a professional observatory might cost several thousands of dollars.

A&S: It sounds like a terrific new project. Do you feel any sort of nostalgia, though, for the asteroids? Did you hope to continue with that?

Tucker: Boy. When I was the middle of doing the asteroid searching, it was such a pleasant routine to come home in the evening and look through the images that I’d collected the previous night.

I could spend anywhere from 3 to 5 hours looking through the previous night’s images looking for asteroids, comets, or whatever I could find. And every two years I would move the pointing of the telescopes to look at a new area of sky. And with the changing of the seasons I would see new parts of this region of sky that I was searching—it would be basically a band around the sky 8/10ths of a degree wide—and I would become very familiar with faint galaxies, clouds of glowing gas, things like that. And it was such a privilege to be able to gaze up into the universe. I was seeing objects that were almost a million times fainter than could be seen with the unaided eye.

Even though I was looking for asteroids and comets, my mind would wander, and it was quite something to contemplate that I was gazing across such a vast distance, seeing such marvels.

So, yeah, it was thoroughly enjoyable, and I expect to occasionally do it again, just because it’s so intellectually stimulating. That’s the only way I can put it, I guess. It’s just that now, with the professional surveys, the likelihood of finding anything interesting has fallen quite dramatically, as far as asteroids and comets. In the past year or so they’ve really been beating me to the punch. I guess that’s good, because that basically indicates that the question of finding objects before they hit the earth is being addressed. It’s a matter of going to fainter and fainter objects, which means basically smaller objects. And although the likelihood that some small object will strike the earth is much greater than a large object, nevertheless, the damage they cause would be far less. It’s not so much an extinction-level event, as maybe a city-buster or some bright fireworks. Of course, even if it’s a so-called city-buster, the likelihood is that it’s going to hit out in the ocean somewhere, or some desolate place like Sudan where there isn’t anybody to take notice of it. I was never really worried about the impact threat. I thought of what I was doing as more of an entertaining sport rather than saving the planet or anything like that. It was a fun thing to do with the instruments I had.

A&S:  What to you made it a sport? The competition?

Tucker: It was fun. It was one of those types of endeavors where every once in a while I could get out on the field of play with the big guys—like on a professional ball team—and score a point once in a while. Astronomy is one of those rare human endeavors where, under the right circumstances, an amateur can still score a point, i.e., make a discovery, in spite of all the efforts of the professionals.

Working as I do, in a support position for professional astronomy, one thing I realize is that professional astronomers spend a lot of their time sitting in an office. They don’t often get to a telescope. They have to apply months in advance for telescope time. They might get a few nights, and if they get bad weather it’s a wipeout. Whereas an amateur, the telescope may be in their back yard and they can get out there and observe every clear night, which is pretty much what I do. And it’s just a matter of time before nature looks kindly upon the person who is spending the time, and a discovery will present itself. It’s a numbers game to a large extent.

A&S: How did you become interested in astronomy, and particularly in asteroids?

Tucker: As far as becoming interested in astronomy, that was about when I was 15 or 14, in 1966. I was still in high school, and I picked up an astronomy book in the library, and read about something called the Zodiacal Light, which can be seen as a false twilight, the light reflected from tiny dust particles in orbit around the sun along the ecliptic. And I thought, Oh, that’s interesting, I’ll get up in the morning and see if I can find it. Well, I didn’t actually see it, but I got up in the morning, and it was the first time I had arisen so early, and the morning time is so different than the evening. In the evening there are lots of people noises, there’s all sorts of activity and such, but in the morning, it was so quiet, it was like I had the whole world to myself. And the sky was clear and quite spectacular, and I was so taken with it, that I decided to get up every morning at 4 o’clock just to watch the sun come up and look at the sky.  And it was only a few months later, 1966 in November, that I happened to get up one morning and went out to look at the sky, and was greeted by the great Leonid meteor storm of 1966. And I didn’t realize at that time that I was seeing a once-in-a-lifetime thing. I thought, Oh! So that’s a meteor shower! Never realizing that I would never see anything that spectacular again in my life, most likely. I saw the Leonids back in 1999 and 2000, and they put on a good show, but it was nothing like what I saw in 1966. So that basically captivated my interest for the rest of my life.

How did I get into asteroids? Meeting the right people. When I joined the Air Force in 1972, I had an interest in astronomy, and I had just recently purchased a Government Printing Office book about asteroids, and I took that with me to Thailand, something to read, astronomical, in my spare time while I was there.

I read a lot of the articles, there not being a lot else to do in Thailand except go to work, and read about astronomy! So I read a lot of the articles about asteroids. And then a few years later, when I was a graduate student in Santa Barbara, in California, at UC Santa Barbara, I met Dr. Alan Harris, who is a well-known asteroid astronomer who worked at JPL—sort of like a sabbatical sort of thing, he was teaching at the university, and I was his lab assistant. And we collaborated on—I was tinkering together some photometric equipment, and he realized that this was exactly the sort of thing that would be necessary for observing an occultation. (An occultation is where an asteroid passes in front of a star, causing the star to blink out for a time.)

And he helped me participate in an effort involving many observers scattered across Southern California to observe an occultation of the star by, I think, Juno, I recall, December 11, 1979. And it was a successful event. I recorded the reduction in light due to the passage of the asteroid in front of the star, and provided the timing of the event, and that permitted him, along with the observations of the other people, to make a precise determination of the actual size of this asteroid. Back in those days, that was about the only way you could actually directly measure the size of an asteroid. So that was quite exciting.

Later, before I finished graduate school, I came to Tucson, Arizona, as a summer student in 1979, and I met David Tholen, who was a graduate student in planetary sciences at the time, and we got to talking about asteroids quite a bit. And then later, when I finished graduate school, I came back to Tucson to work at the multiple-mirror telescope observatory. I have to explain that I met David Tholen because his roommate was from Venezuela and went back home for the summer, and so he needed a temporary apartment roommate to help pay the rent while his regular roommate was in Venezuela, I was the summer replacement, you might say.

Later, when I finished graduate school, I came back to work at the multiple-mirror telescope observatory, his roommate moved out, and so I moved in, and it was like we picked up where we left off, talking about asteroids and stuff. And I’ve maintained this friendship with David over the years. In 1996, when I set up my backyard observatory, he encouraged me to start participating in measurements of positions of asteroids. And that’s what led to all the other things that I’ve been doing with asteroids over the past 14 years.

A&S: What did you do in the Air Force?

Tucker: I was an electronic warfare systems specialist, basically advanced electronics that prevent the aircraft from being shot down by missiles and anti-aircraft artillery. The experience in the Air Force was excellent, because the nature of electronic warfare involves the most leading-edge electronics. Absolutely state-of-the-art, the latest technologies, and I encountered a lot of experience with microwave-type techniques, digital processing and such, so that was a wonderful experience that helped set the stage for my later Master’s degree in scientific instrumentation. I took, essentially, my interest in astronomy, and my experience and professional expertise in electronics, and combined it to become an instrumentation engineer supporting astronomy.

A&S: That’s a question I wanted to ask you—how your work as an astronomer compliments your professional work.

Tucker: They absolutely do. I work as a support engineer professionally, supporting astronomy, and then in my spare time, I observe as a means of creative expression. I get to use some of the instruments—not the ones I help build, but ones that are similar, smaller, intended for the amateur-size or scale of operations, but it permits me to actually do some observing and become acquainted with the problems involved in trying to get the starlight onto the CCD detector. One of the things I’m doing right now is spectroscopy; taking starlight and dividing it to its colors (dispersing it into its component wavelengths), and determining the physical nature of some the objects I’m looking at. It’s quite fascinating, being able to do some of the things that I’ve only seen previously described in textbooks. It used to be that spectroscopy was the realm of big-time professional observatories. But with the CCD detectors, they’re so sensitive to light that you can now do in a backyard with a relatively small telescope what previously was only possible photographically with a very large telescope. I can go back to astronomy magazines that came out in the 1950s, and they may have articles describing what is being done at some observatories with a spectrograph, and I can now do that with a relatively small telescope in my backyard.

A&S: That’s wonderful.

Tucker: It is. It’s amazing. The old photographic films would only detect about one percent of the light that struck them, but the modern CCD detectors will detect to 80 or 90 percent of the light that strikes them. It’s that difference in sensitivity to light that makes all the difference in the world as far as amateur participation in astronomical research.

Astronomy touches upon more other sciences and technologies than just about anything I can think of. In the pursuit of my interest in astronomy, I have learned electronics, mathematics, physics, chemistry, optics and optical fabrication, geology, metal-working, welding, pouring concrete, and a host of other things. I've also enjoyed some wonderful friendships and shared great experiences. I think all children should be exposed to astronomy, given a chance to look through a telescope at the moon or the rings of Saturn, and perhaps let the interest grow and lead where it may.

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