There’s a Comet Coming

Beginning on 12 March, a comet will be visible in the early evening sky. There’s information on where in the sky to look here.comet

Meanwhile, here’s a view of a comet taken by Wide-field Infrared Survey Explorer or WISE. This comet, known as C/2007 Q3, was discovered in 2007 by Australian observers. The snowball-like mass of ice and dust spent billions of years orbiting out in the deep freeze of the Oort Cloud, the cloud of comets surrounding the Solar System. Eventually, it got diverted from of this original orbit and onto a course bringing it closer to the Sun. Sunlight warmed the comet, causing it to shed ices and dust in a long tail that trails behind it.

In October, 2009, it passed as close as 1.2 astronomical units from Earth and 2.25 astronomical units from the sun (an astronomical unit is the average distance between the Sun and Earth). In this infrared image, longer wavelengths are shown in red and shorter wavelengths are blue. The comet appears red because it is much colder than the background stars. Colder objects give off more of their light at longer wavelengths. An ice cube, for example, pours out a larger fraction of its light at longer infrared wavelengths than does a cup of hot coffee.

Image Credit: NASA

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