|Comet Garradd can be seen right now with binoculars in the constellation Sagitta
CREDIT: Starry Night Software
This story was updated at 5 p.m. EDT.
Skywatchers often ask “When’s the next comet?” In fact, if you’re prepared to do a bit of searching, there are always several comets visible in the night sky, including two right now.
Some comets are like old friends, they keep coming back at regular intervals to visit. These are called periodic comets; Comet Halley was the first such comet to be identified, by Edmond Halley back in 1705. It returns to the inner solar system every 75 to 76 years; its last appearance was in 1986 and its next will be in 2061. At present Halley is out just beyond Neptune;s orbit.
Other comets are one-time visitors: they come in to visit us from the Oort Cloud, warm themselves for a few months by the sun, and then head back out to the farthest reaches of the solar system. [Best Close Encounters with Comets]
There are two comets currently visiting the inner solar system — comet Elenin and comet Garradd — so the next two months will provide some excellent opportunities to observe these unusual visitors. The sky map of the two comets here shows they locations over the next few weeks.
All comets share one characteristic: they are like “dirty snowballs” in their makeup. Their nucleus of rock and ice, when warmed by the sun, sheds its ice which forms a graceful tail as it’s swept away by the solar wind. Because it’s the solar wind that drives the gas and vapor away, comet’s tails always point away from the sun.
In the sky, many comets appear like ghostly fingers pointing down towards Earth. That is one reason why comets have traditionally been viewed as harbingers of death and disaster. To astronomers, on the contrary, they are objects of great beauty and attract close scientific scrutiny for the information they reveal about the ancient history of the solar system and its farthest reaches.