Fall 2004

Are the Stars Out Tonight?: An Interview with Robert Evans

Scanning the skies with the world’s greatest supernova hunter

Jeffrey Kastner and Robert Evans

While the increasing availability of highly sophisticated computerized search and detection technologies over the last few decades has put serious astronomical study within the reach of the average hobbyist, a few amateurs continue to study the heavens—and even make important contributions to science—with old-fashioned tools like sky charts and small telescopes. One of the most extraordinary of these lay astronomers is Robert Evans, who for nearly half a century has been searching the sky for evidence of supernovae, the massive explosions that signal the death of stars. Utilizing nothing more than modest telescopes sited in his own backyard and an astonishing visual memory for star fields and galactic features, Evans has discovered 39 supernovae, the most of any visual observer in history. A pastor retired from Australia’s Uniting Church, Evans spoke on the phone with Cabinet editor Jeffrey Kastner from his home in the Blue Mountains, some 50 miles west of Sydney.

Cabinet: How did you first get interested in astronomy?

Robert Evans: My father, who was a botanist, had a very modest understanding of the constellations, the southern ones especially, and knew the names of some stars. I was in primary school when he started to introduce me to these things and I had an ancient star map, an atlas really, borrowed from the university library. This was the late 1940s. My older brother became an optometrist, and he made me a telescope out of a spectacle lens, a microscope eyepiece, and some rolls of paper when I was in high school. It was the only thing I had—it was modestly better than the naked eye, but not a lot. And that got me interested. After I left school, I bought other telescopes. I initially liked to look at globular clusters and star clusters, double stars.

But then in the mid-1950s, you decide to start looking for supernovae. What was going on at that point in terms of people searching for supernovae, either scientists or amateurs?

Well, amateurs zero. In the scientific community, the main person was Fritz Zwicky at Caltech.

Why were you interested in supernovae?

In the 1950s, when I started using a 5-inch telescope to try to look at galaxies, only about 50 or 60 supernovae had been found. I guess the fact that not much was known about them appealed to me.

Maybe we should back up a bit. What exactly is a supernova?

It’s a star that explodes, entirely or almost entirely. There are two explosion mechanisms. One of them involves a star at least five or ten times larger than the sun that runs out of nuclear fuel. The big stars burn up their juice a lot faster than the smaller ones. Once the nuclear fusion process reaches a stage where the core of the star, being made out of iron, is involved, the process is unable to continue any longer. I think that process is reasonably well understood by scientists nowadays—it’s called a Type 2 supernova and the supernova in the Large Magellanic Cloud is one of those kind and has been studied in a lot of detail. The other process creates what are now called Type 1a supernovae and no one’s ever observed one of those sorts of stars exploding, but you can get spectra of the things and use a supercomputer to create models.

In terms of visible phenomena, is there a difference between the two types?

Type 1a supernovae are generally much brighter than the others.

Have there been supernovae sufficiently close to the earth that they could be seen with the naked eye?

There are, I think, six well-recognized examples since the time of Christ—in 185, in 1006, in 1054, in 1572, in 1604 and, of course, there was one in 1987, the one I mentioned that appeared in the Large Magellanic Cloud. While it was about 170,000 light years away and was not one of the brightest kinds of supernovae by any means, it was still quite easily seen with the naked eye. A Type 1a supernova at that distance would have been several magnitudes brighter still.

Do supernovae have a kind of period? Say you observe what you think is a supernova on Tuesday. If you look at it again on Sunday, does it look different?

It might. With a Type 1a supernova, the explosion probably occurs largely in a part of the spectrum that isn’t visible, but visual light gets brighter over, say, two weeks, until it’s some millions of times brighter than it was before. And then it reaches a peak that might last a week or a few weeks, and then it might tail off in a certain characteristic way. Now, how long you’re going be able to see that depends on how far away the galaxy is. If the galaxy is quite nearby, say, only a couple million light years away, you could see it probably for some years, if you had the right equipment.

Do particular galaxies or particular kinds of galaxies have a propensity for supernovae? Are there certain places where one might have better luck looking?

Spiral galaxies also produce Type 2 supernovae, large stars that explode, but the elliptical galaxies don’t produce those. So spirals are a better place to look, because they produce both kinds.

When you first began looking for supernovae, it took quite a while before you had much luck, and part of what you were doing was familiarizing yourself with the galaxies.

Yes. In the 1960s and 1970s, when I started, there were only published photographs of some of the galaxies. There was a survey that was produced in the 1950s called the Palomar Observatory Sky Survey, but it didn’t cover all of the southern sky. And also, sets of that were quite expensive, and the ones that existed in Australia were not open to the public.

So how did you familiarize yourself with the sky?

Just by repeated observations. The problem is that as you get used to the appearance of a galaxy, you begin to see more details in it, particularly under varying observational conditions, and you never know if any of these new details might be the kind of thing you’re looking for, as opposed to just something you hadn’t noticed before. And so you have a lot of false alarms. And back in the 1970s there was no real way of checking those things out. So I tried turning my 10-inch telescope into a photographic telescope, so I could take my own pictures. But it didn’t work—the kind of equipment you need for taking time-exposure photographs of the sky is of much better quality than what I ever had, so that didn’t work at all. So I gave up for quite a while. I still used to observe the sky from time to time, but I didn’t have any urge to do too much of it. It wasn’t until the end of 1979 and 1980 that I started doing it again, and by that time I had come across a group of amateurs in Brisbane who were making charts of the brighter galaxies to act as reference materials. I also came into contact with a fellow who worked at the Anglo-Australian Observatory, the main research observatory here in Australia, who allowed me to have access to the new photographic southern surveys.

Could you describe what a night of observing was like in those days?

Yes, well, you had to have an atlas, which allowed you to locate the galaxies, and then you could use a little finder telescope on the side of the big telescope to pinpoint the spot, and then you could find the galaxy using the main telescope. And so I would observe as many galaxies as I could on a reasonably regular basis. By 1980, we had moved up the north coast of New South Wales, and so there were quite good observing spots in the backyard and the churchyard, but the weather was less cooperative—only about a quarter of the nights were fine. And I would just try to observe as many galaxies as I could and as quickly as possible; and by observing regularly you could get used to what the galaxy was supposed to look like and, of course, you had a photo of it inside if you got suspicious about anything.

And you would look at hundreds of galaxies in one night.

That’s right. You take a few seconds to find one and then ten or twenty seconds to look at it and then you move on to the next one.

Robert Evans ready for action (ca. 1988). Photo copyright Roger Ressmeyer/Corbis.

Talk about your first discovery.

That was in early 1981. I was still using the first of these charts that had become available from the people in Brisbane. I was observing as many galaxies as I could, but it was a period of the year when there’s a lot of cloudy weather. I remember weeks of no observing. But then, in late February 1981, I observed this particular galaxy, and noticed there was a faint star in a different location than what was indicated by the chart. Tom Cragg, the fellow who worked at the Anglo-Australian Observatory, had agreed to check up on things I was suspicious about and he observed it also. But because it was the first discovery in this kind of work we were doing, he was a little frightened to announce it without getting more verification. So he waited until one of the professional astronomers had observed it with one of the main telescopes, and then the discovery was reported. Actually, there were three bright supernovae that appeared in about two-and-a-half weeks around that time.

Is that unusual?

Yes, quite. I missed the second one because after I saw it I looked at the chart and thought, “Oh well, that’s not one,” and then I found the third one, so I found the first and third in about fifteen days. I kept on increasing the number of galaxies I looked at and by the end of 1984, I had 10 discoveries—4 each in 1983 and 1984 and then about the end of 1985, I got a small amount of government funding to get a 16-inch telescope, which improved my ability to see things a bit.

Were you aware of others who were doing this kind of work, or were you always very much on your own?

In the first half of 1980s, there were several Japanese amateurs who made discoveries using photographic equipment.

Which means you go out and shoot photos of galaxies and then come in and look at the pictures?

The professionals, of course, used to do that. There weren’t many discoveries, perhaps 15 a year or even fewer, and the professionals found most of them. They’d either stumble on them or in some cases there were photographic searches done with wide-field Schmidt camera telescopes and they had to use photographic methods—CCDs didn’t exist yet.

What are CCDs?

It stands for charge-coupled device. It’s an array of pixels that feed into a computer, basically a kind of light detector.

So there are three different types of observation: you in the backyard pointing your telescope at things; people taking photographs and then looking at them …

And that’s all that existed in the early 1980s.

So it wasn’t until the 1980s that computerized observation came into use?

The CCDs began to be used in the second half of the 1980s. Of course the first efforts at making a fully automatic search were not successful because the computers weren’t good enough.

An automatic search is a computer that uses coordinates to move the telescope to certain points in the sky?

It would all be programmed in beforehand and then it would take a picture and compare it with a file picture of the objects in that view. It’s actually quite a complicated process, because the two pictures have to be compared so you can subtract one from the other. It took a number of years to develop the program and for computers to be made that had enough capacity to use it. Of course, it’s a relatively simple matter nowadays—you can do it with a laptop.

And through all these technological developments, your procedure for observation was largely unchanged. It was just simply you looking and then noting it and then telling someone else who would then examine your observation.

Yes, it had to be verified. Nowadays they’ve tightened up the rules about reporting things and you’ve got to have a CCD picture verifying it with exact measurements of the position of the new object and how bright it is and all the details about it so that satellite telescopes can be pointed at it, if necessary.

What is the body that says a discovery is official?

It’s an office at the Smithsonian Institution in Cambridge, Massachusetts, called the Central Bureau for Astronomical Telegrams. It relates to the time when discoveries were announced by telegram, which no longer happens, of course. All the messages are sent out by email.

I first came across your name in Timothy Ferris’s book The Whole Shebang, where he cites you as holding the record for having made the most visual supernovae discoveries of anyone in history. What is the total now?

I’ve made 39 visual discoveries, but I have found a few others by other means, as well—by looking at photographs.

Is your name somehow attached to these discoveries?

Not like comets, which are named after the person who finds them. Supernovae are named by the year in which they appear—and then there’s a letter or a series of letters after the year that indicates the sequence. In the early days, when fewer than 26 would typically be found each year, they just used a single capital letter. But now, they might find several hundred in a year, so after number 26 they use two lower case letters, starting with aa, ab, ac, ad. Nowadays of course with supernovae being used as a major means of studying distant parts of the universe, there’s a whole industry of professional scientists working on supernovae.

Talk a bit about how supernovae are important to our current understanding of cosmological issues.

Cosmology is concerned with questions about the origins of the universe and how it might end and what its general history is. One thing that astronomers have been trying to study is the expansion of the universe. It has been believed since 1924, when Hubble discovered that the galaxies were traveling apart, that the universe was expanding. And astronomers have been trying to figure out what that meant and what it implied for the origin of the universe. This is where the theory of the Big Bang came from, of course—because the galaxies were going away from each other, there must have been a time when things were closer together. It was generally believed that the galaxies would either just continue steadily going apart or else, because of gravity, their expansion would slow and then they would start coming back together again. Supernova studies were one of the means for testing this out. About 70 percent of Type 1a supernovae are of a standard character. In the 1980s and early 1990s, a good proportion of the nearby supernovae that provided the landmark information were actually found by amateurs and a good many of them were my discoveries. Many were visual discoveries, whether mine or somebody else’s. So amateurs made quite a contribution to that. For example, a number of nearby supernovae that were found visually by amateurs helped to provide the key so that peculiar Type 1 supernovae could be distinguished from those which shared the standard character. In this way, Type 1b and Type 1c supernovae were recognized, as well as Type 1a supernovae that were too faint or too bright for use as standard distance indicators. During the 1990s, the professionals developed two research groups that began searching for supernova explosions in remote parts of the universe in order to find out about the history of the universe. And they began to find some of these, and the results of the two groups who were working on it were published in about 1998, I think, and they both said that based on what they could tell about distant supernovae, the expansion of universe was actually accelerating, not slowing down.

Which was counterintuitive at that point.

It was heretical, really, and no one wanted to believe it. And then they managed to find a supernova on one of the Hubble Telescope deep-sky surveys. There were pictures taken in 1995, and then again in 1997, of the same tiny spot in the sky, exposing for 100 hours with the CCD so they were seeing galaxies that were more than halfway back to the beginning of time. And they managed to find a supernova in one of these pictures and had enough information to determine that it was probably a Type 1a supernova at maximum brightness and they discovered that back at that time, the universe had in fact been slowing down. So it seems in the first half of the history of the universe, it started out expanding rapidly, and then slowed down because of the force of its gravity. But at a certain stage, the material in the universe got too thin and the gravity no longer slowed it down and it began accelerating again. And that’s the part of the universe we’re in now. Now this has all been the result of supernova study. Amateurs are not able to really contribute to that kind of thing now. But what is happening is that there are amateurs who have enough money to afford automatic search equipment, which you can almost buy off the shelf now. So there are these groups of professional astronomers that search out in the depths of the universe and there are other professional groups that search locally, yet about 30 percent of supernovae that are found are still found by amateurs who are using CCDs and computers and modest telescopes, so amateurs are still making a contribution. But visually now, very few are found.

Do you still do it?

I still do some and there are some other amateurs who still do a bit of visual searching.

As the years have gone by, has your ability to do visual searching changed? Has your sense of the sky changed?

The process is still the same—I can forget details if I don’t look at a galaxy for a period of time. But there are also galaxies I’ve looked at so many times, I’m not likely to forget what I’ve seen.

Much has been made of your unusual ability to memorize the sky. Do you have this talent in other aspects of your life?

It’s hard to say. I had a better memory for learning stuff for exams when I was in my 20s, though I never did enormously well on exams. I’m good at visual observations and patterns of things, I suppose. My father could remember the botanical names of a thousand or more species of plants that grew around Sydney and the Blue Mountains here, so he had a detailed memory of those kinds of things.

I personally find the experience of looking at the stars and thinking about the cosmos to be, for lack of a better word, a spiritual one. You’re a minister. Is your astronomical quest in some sense spiritual?

Well, there are certainly times when I look at photographs of the depths of the universe and I’m blown away because I know what the pictures mean. It doesn’t tend to happen so much when I’m looking through a telescope, though, because I’m busy. However, when a person can recognize nature as part of God’s creation, which shows His wisdom, beauty, and power, then I find that it becomes a great way in which the glory of God is displayed. This is true whether we look at big things, or very small things. My father used to see this in the botanical world. I can see it in stars and galaxies, and in the depths of the universe.

Detail from the Hubble Ultra Deep Field, 2003–2004. This million-second-long exposure is, according to NASA, “the deepest portrait of the visible universe ever achieved by humankind.”

Robert Evans is an amateur astronomer and a retired minister in the Uniting Church of Australia.

Jeffrey Kastner is a Brooklyn-based writer and senior editor of Cabinet.

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