The Minor Planet Center is at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and operates on behalf of the International Astronomical Union. Brian Marsden has directed the MPC since 1978. From 1968 to 2000 he also directed the MPC’s sister organisation, the Central Bureau for Astronomical Telegrams. These jobs entail checking and logging observations of asteroids, novae, supernovae and comets, and naming any new discoveries. Marsden first began making orbital calculations as an amateur when living in Cambridge, UK, but turned professional after taking a PhD on Jupiter’s moons at Yale University. He has successfully predicted the return of hundreds of lost asteroids.
You have daily contact with a lot of amateur astronomers and have got to know many of them. What sort of people are they?
They tend to be people with considerable persistence. Most amateur astronomers are somewhat possessed by what they are doing. By definition an amateur is someone who’s retired, or who’s got another job, who puts in a day at the office and then gets home and sits at the telescope. There are relatively few female amateur astronomers. There are many professionals, but the only amateurs I can think of are a woman in Italy who regularly makes observations of asteroids and one in Japan, who does some work on supernovae – exploding stars – with her husband.
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Many observations today are made by large professional surveys that search for near-Earth asteroids by making tens of thousands of observations each night. What can amateurs contribute?
Most of the work that amateurs do involves following up on observations that the large surveys have done. When we get reports of an object that could be a comet or a near-Earth object, we post a rough prediction of its orbit on a web page. Then people let us know where they see the object, which helps us refine its orbit to the point where we can number it. We have between 120 and 150 observatories doing this follow-up work at any given time, and probably 90 per cent of them are amateurs.
An amateur astronomer is often seen as someone gazing up through their telescope from their backyard. Does that still hold?
Nowadays people have very automated set-ups. They have telescopes taking film or digital images – with charge-coupled devices or CCDs – of the sky and often they study these from the comfort of their homes. It is a far cry from the rugged astronomer in his backyard. We get relatively few visual reports nowadays. They are so hard to do.
The CCD is particularly suited to spotting supernovae as you can compare the new image with the archive. In the UK two amateurs, Mark Armstrong and Ted Boles, are doing a great job on supernovae using CCDs. Armstrong operates his telescope by remote control on the roof of his house in Kent.
Other amateurs find supernovae without realising. They make their images available online and then professionals scrutinise them using more advanced software. Nowadays you don’t even need a telescope to do astronomy, because you can look at professional images or the images of other amateurs. I myself started out as an amateur, but I was never an observer. I made orbital calculations.
However, the first amateur to start discovering supernovae – Bob Evans, a clergyman in Australia who has been doing it since 1981 and has found more than any other amateur – did it entirely visually. He used no photographs or CCD images.
How would you go about making a visual discovery?
You need to look at hundreds of galaxies per night to have a chance of seeing one. Evans would simply look from one galaxy to another and he had all the galaxies memorised, so he would know if he saw a change. He would know if the galaxy didn’t look right, if perhaps there was a new star or a supernova in it. And rather than write it down at the time, he would just remember where he had seen it, so he could look at more galaxies each night. Then he’d write it down the next day.
The British amateur astronomer George Alcock worked like that too. After finding four comets he decided comets, with their characteristic fuzzy appearance, had become easy for him, so he tried novae – stars that brighten suddenly and temporarily – and he found five of them too. He had to learn all the stars so he’d know if there was something new there. When you think about it, that’s a tremendous thing.
Are amateur observations really as good as professional?
Most amateurs produce very high-quality data. They make mistakes, but so do professionals. For example, we’ve actually had quite a few reports of Neptune as a nova from professional astronomers, in one case from the director of an observatory. I usually reply with a one-word message, “Neptune”. One thing that happens twice a year to some amateurs is that they get their observations systematically wrong, and then we realise they neglected to make the change from daylight saving time. The professionals don’t make that mistake.
Most discoveries are made by professional surveys, yet the amateurs play a crucial role. How do they get credit?
This is one of the problems we have. The surveys notch up lots of minor planets, but their work is dependent on what we do here at the Minor Planet Center to link their observations to those of others, and on the amateurs who make those other observations. So does the survey’s observation really count as a discovery? It does, when it reports it first. However, surveys often don’t realise what they have seen and so don’t report the object as new. So we give extra credit to people who are among the first to report an object and who know what they have seen.
For example, in 1983 Alcock reported his fifth comet. I had heard that people working with the Infrared Astronomical Satellite had seen some kind of fuzzy object a week before. When I heard about Alcock’s comet I contacted them and told them to send me their data by the next day at noon or I would call it Comet Alcock. They sent in their data, and in the meantime another independent observation came in from Japan. So we called it Comet IRAS-Araki-Alcock. IRAS saw it first, but they hadn’t even looked at their plates properly. I really think that if you’re making a discovery, you should appreciate that you have a discovery. Alcock was like that: he really knew when he had something special.
It’s too bad we can’t give the amateurs more credit. I’m a firm believer in giving credit. Amateurs are going out of their way to do this work.
How many amateurs are usually involved in the discovery of a new object?
I’ll give you an example. A large asteroid, 3 or 4 kilometres across, was spotted on 22 May this year by the LINEAR telescopes in Socorro, New Mexico, which are run by the Massachusetts Institute of Technology’s Lincoln Laboratory in Lexington. A professional Czech observer got onto it half a day later, and we refined the orbit further. Later we got reports from amateur astronomers in Mallorca in the Canary Islands, from an amateur in Lafayette, Indiana, and from the Tenagra II telescope in Arizona which I happen to know is owned by amateur Mike Schwartz. We then knew exactly where it was and so 24 hours after the first sighting we sent out our announcement. The interesting thing was that the final observation was made by Paulo Holvorcem, an amateur astronomer who is a professional mathematician and wasn’t even at a telescope. He was looking at Schwartz’s images on the internet. The telescope was in Arizona, but he was in Brazil.
This is such a bright object that I’m quite surprised no one had seen it before. We might well get a report of a prior sighting. Some amateurs do archive work. Reiner Stoss, who is in Germany but uses the Mallorca observatory, likes to look at old photographic plates to see if he can find a previous sighting of a reported new discovery. If he does that for this asteroid, and the orbit matches up, the eventual credit for the discovery may not go to LINEAR.
Where are most of your amateurs based?
It’s very odd, but our most active amateurs are in the UK. It’s surprising because they have inferior skies. Then there are people in the southern hemisphere and they really have an advantage because the professional surveys don’t look there.
You are responsible for evaluating all astronomical observations. Sounds like a huge job…
It is. We get a few hundred reports every day, some containing just one observation, others several thousand. The LINEAR telescope can report over 60,000 observations in one night. Yet we have only three people here to process them all. The number of observations has vastly increased. The first asteroid was logged in 1801, and we reached 10,000 in early 1999. But since then, we’ve logged another 55,000. The large increase is mainly the result of the huge sky surveys for detecting near-Earth asteroids.
Many of your colleagues at the centre have been with you for quite some time. Do you need a long perspective to do the job well?
Dan Green, who runs the Central Bureau for Astronomical Telegrams, which is responsible for reporting on astronomical objects that are not asteroids, has been here since 1980. My associate Gareth Williams has been here 13 years. Yes, you need to understand what has happened in the past. So many professional astronomers don’t seem to have an appreciation for anything that happened more than five years ago. A lot of the amateurs are in it for a long time. They might do it for a few years and then have a family and then go back to it. I certainly think I have good successors in Dan and Gareth.
Didn’t Gareth marry your daughter?
Yes he did. He came here in 1990, the year my daughter joined the US navy, so in the beginning they only met a few times. But she came back here two years ago and was living in our basement and they were both around and were married last October. We fell behind in orbital calculations that month.