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Supernova 1987A: the Discovery

Week of February 21, 2000

Irony has a way of being so, well, ironic sometimes. I have been writing these Snacks for three years now, and my plan was-- and still is-- to talk about things I find interesting about astronomy, and hope that you find them interesting as well. So how ironic is it that in all this time, I've never written about the one object I find most interesting of all?

I have always loved supernovae, stars that explode. There's something very dramatic about such a titanic display of force. When a star explodes, in one second it emits as much energy as the Sun does in its entire lifetime! Luckily, these events aren't too common, and tend to happen pretty far from the Earth. They are so bright, they can be seen clear across the Universe, a fact which may have startling implications for our eventual fate.

This week marks the anniversary of perhaps the most important supernova we've ever seen. It was the most closely studied supernova of all time; for one thing, it was the brightest supernova since the invention of the telescope! It revolutionized our ideas about how stars explode, why they explode, and what happens after they explode. For the next few weeks I'll take a look at different aspects of this star, and how it changed astronomy. It certainly changed me! Even the discovery of this object is amazing, and so we'll start off this mini-series with just how this star exploded into our lives.

Late in the evening of February 23rd/24th*, 1987, an astronomer named Ian Shelton was taking images of the Large Magellanic Cloud (LMC), a satellite galaxy of the Milky Way. He was using a small telescope to take images of the LMC to check for variable stars and novae (novae are stars that suffer minor explosions, and are far less energetic then their big brothers the supernovae). Shelton was taking a photographic plate of the LMC at about 1:00 a.m. local time that night.

image of supernova in the LMC At roughly the same time, Oscar Duhalde, an operator for a telescope not far from where Shelton was at the same observatory, decided to go outside to take a break from using the 'scope. Using nothing but his own eyes and his intimate knowledge of that area of the sky, he noticed a star in the LMC that wasn't there the last time he looked. He was actually the first person to see the supernova! Unfortunately, he didn't report it to the other astronomers, perhaps because he had been working so hard, and he simply forgot. Shortly thereafter, Ian Shelton developed the plates he had been taking of the LMC and immediately saw the new star. He went over to the other telescope and told them what he had found; Duhalde then mentioned that he had seen it earlier. At this point, the four astronomers (Shelton, Duhalde, Barry Madore and Robert Jedrzejewski) promptly went outside to see for themselves this new supernova.

And a supernova it was. They knew this immediately; it was far too bright to be a simple nova in the LMC. They sent a telegram to Cambridge, Massachusetts, which is the clearing house for astronomical discoveries. A confirmation was sent by another team in New Zealand just half an hour later. It was by this margin that Shelton became known as the discoverer of Supernova 1987A.

Perhaps even funnier is that the supernova had actually been photographed even earlier. Robert McNaught, in Australia, was also photographing that area of the sky. However, unlike Shelton, he didn't notice the new star until later. Other photographs by other observers were also made before Shelton's. However, he is the one who first reported it, and so he is the one credited with discovering what would later turn out to be the most studied and important object of its kind.

Next week we'll talk about just why a star like this explodes, and how SN87A surprised us all by not following the rules.

*Note (Feb 27, 2007): I originally had the date listed as just February 24 for the discovery. But I just received a note from Ian Shelton (!), the man himself, saying that it was the night of the 23/24. Given that Australia is on the other side of the International Date Line from the U.S. (from my time zone, they are 19 hours ahead, which I like to think of as "5 hours earlier but a day ahead") I was trying to be squishy on the date. Darn scientists and their attention to details!

©2008 Phil Plait. All Rights Reserved.

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