Today’s Factismal: The comet Pan-STARRS and the new Moon are visible tonight just after sunset.
Something that is easy to forget is that science didn’t just happen in the time of the Greeks, or during the Renaissance; it happens all the time. It is happening NOW. As you read this article, a new comet is swirling through the sky.
Known as Comet Pan-STARRS (named for the Panoramic Survey Telescope and Rapid Response System, an automated telescope that found the comet), this new pearl in the night-time sky is currently visible just after sunset. To see it, go outside about half and hour after sunset (or watch the sunset and wait thirty minutes). Then look to the new Moon, about two fists above the horizon in the western skies (the further north you live, the closer to the horizon the comet will be). Right next to it will be a bright dot with a thin, wispy plume of material. That’s the comet. The comet should be visible to the naked eye for the rest of the week, and can be seen through a pair of binoculars for the rest of the month.
Comet Pan-STARRS is surprisingly bright. This is its first pass through the inner Solar System, and most new comets aren’t very bright. But the comet has just zipped past the Sun and has outgassed a significant amount of material, making it very bright. But it will get fainter very quickly as it heads back out into the Oort cloud where comets hide.
It turns out that the reason that comets get brighter as they get nearer the Sun tells us a lot about how comets are made. The two most important parts of a comet are the nucleus, which is the main blob of material, and the coma and tail, which are made up of dust and gas thrown off by the nucleus as it heats up. Thanks to spectroscopy, we know that the nucleus is mainly made up of ices (water ice, ammonia ice, and even methane and carbon dioxide ice) with pieces of rock for texture; this mixture of rock and ice is why comets are often called “dirty snowballs”.
The ices had to form far out in the outer Solar system; had they formed closer in, then the ice would have boiled away as it did on the early Earth; all of our water was delivered by comets during the late heavy bombardment. So comets are among the most primitive things in the Solar System and tell us much about what the nebula that we formed from was like. That’s why there have been so many missions sent to capture pieces of comets for study.
The ices heat up as the comet gets closer to the Sun, and spews out gasses that form a globe called the coma. The gasses in the coma then become ionized and get dragged out by the solar wind forming the long glowing tail that is characteristic of comets; this gas tail always points straight away from the Sun. Little flakes of rock dust can also be lost. Because the dust is denser than the gas and isn’t ionized, it can form a second tail that curves away from the comet. (So straight tail=gas, curvy tail=dust. Now go impress your friends.) That dust is left behind in orbits that sometimes lead it to fall on Earth as fireballs.
If you miss seeing this comet, never fear: we also expect a second, potentially bigger comet, to come through our neighborhood in November. But if you do, then please post a note about it below. And if you’d rather do your comet hunting from the comfort of your easy chair, then why not try the SOHO Comet Hunting website?