Yesterday, I wrote about the comet 2009 R1 McNaught which is currently in the extreme northern sky in the early morning. By coincidence, just hours after posting it, I got an email from the amateur astronomer Anthony Ayiomamitis (the same guy who took the very cool picture of the ISS and Jupiter in the daytime), who sent me this picture of the comet he took in Greece at just around the same time that post went live:
Wow, very pretty! The solid part of the comet, called the nucleus, is far smaller than a single pixel in this image, since the comet was more than 175 million km (110 million miles) away when he took this shot. The nucleus of even a huge comet is only a few dozen km across, so at that great distance is just a tiny dot. Anthony has details on his observations on his McNaught page.
The comet looks huge — and the fuzzy part can be bigger than planets! — because what you’re seeing is gas expanding away from the nucleus. Far from the Sun that gas is frozen, and the comet is solid. But heat it up, and that ice turns into a gas, creating the comet’s coma (Latin for hair). In that gas methane, water, ammonia, and lots of other things, many of which are pretty nasty.
But why is it green?
Ah, that’s a good question (I’m glad I asked it!) and takes just a little bit of background.
If you’re an early riser in the mid-northern latitudes of our planet (and statistically speaking, the odds are good for the latter part), then there’s a comet you might want to check out.
Comet McNaught (C/2009 R1) is currently moving rapidly across the northern sky, and it’s just on the edge of being bright enough to see with your unaided eye. Over the next few days it may even get bright enough to see easily in dark skies.
This picture, taken by Ernesto Guido and Giovanni Sostero, shows the comet and its long tail. It’s a multiple exposure centered on the comet, which is why you see several star images for each star. You won’t get a view this nice (probably) with binoculars, but you should be able to spot the tail.
The CometChasing website provides a helpful map of the comet’s location over the next few days. On June 21 it’s pretty close to the bright star Capella (one of the brightest in the sky) but it’s not known how bright the comet will be by then. Also, McNaught reaches perihelion (closest point in its orbit to the Sun) on July 2/3, so it’ll be tough to see in a few weeks (though probably brighter; as they gets closer to the Sun most comets get much brighter, but their proximity to the Sun makes them very difficult to spot). With comets it’s always good to get them while the getting’s good. Go look now!
You can find more info on the Cometography site, a spectacular picture on APOD, and an interesting animated GIF showing the motion of the comet, too.
As a bonus for early risers, Jupiter and Uranus will have a series of close approaches to each other in the sky, so you can check that out as well.