Summary: Like football players and rocks stars, a comet can be famous one day and infamous the next. A case in point is Comet Swift-Tuttle. When it was discovered 150 years ago this week, comet discoveries were rare enough that the people who found them became instant celebrities. And by late in the year the comet was visible to the unaided eye, so it gained celebrity status for itself. That celebrity only grew years later, when it was discovered that the comet spawns the Perseid meteor shower, which peaks every August. Swift-Tuttle follows a long orbital path that takes it far from the Sun, so it spends decades in the outer solar system. That made it hard to determine its orbit. In fact, when the comet returned to view in the early 1990s — the first return since its Civil War appearance — astronomers thought there might be a problem — one that changed the comet’s reputation. Calculations showed there was a chance the comet could hit Earth in 2126. Swift-Tuttle is probably about 15 miles in diameter, so a strike would destroy much of the life on Earth. With a little more research, though, astronomers realized that the comet had been seen a couple of times in ancient China. Adding those appearances to the calculations showed that Swift-Tuttle will miss Earth by a few million miles. That’s close enough, though, for the comet to stage a spectacular display in the night sky — one that will take Swift-Tuttle back to the realm of the famous. Script by Damond Benningfield, Copyright 2012 For more skywatching tips, astronomy news, and much more, read StarDate magazine.
