Comets are small, icy and rocky bodies that orbit the Sun. Many comets have highly elongated orbits that extend to the farthest reaches of our solar system, out to a sizeable fraction of the distances to the nearest stars. Out there, in what astronomers have termed the Oort Cloud, a vast collection of comets is thought to exist. Occasionally, gravitational forces within our galaxy will alter a comet’s orbit within the Oort Cloud, so that the comet either escapes our solar system entirely, or moves inward toward the Sun and the Earth.
When comets enter the warm inner solar system, long-frozen ices of water, CO2, CO, and other substances rapidly transition to gases, creating powerful geysers. These geysers propel mineral and organic dust particles into space. The gassy and dusty zone around a comet’s nucleus is called the coma, which typically appears fuzzy and slightly greenish to our eyes. Fine particles and gases in a comet’s coma are pushed outward by the solar wind, sometimes creating spectacular tails. Comets may exhibit two or more tails. In long time-exposure photographs, gas or ion tails typically appear bluish, whereas dust tails are dusky colored.
Want to see a comet this month? During January, Comet Catalina will be moving northward in the morning sky. The Comet will appear as a fuzzy ball, and a short tail may be visible. Comet Catalina likely will be visible with binoculars throughout January. However, comets are unpredictable – they can brighten or fade with no notice. Using binoculars, you may find Comet Catalina high in the east during the early morning of January 2, near the bright orange star, Arcturus. From near Arcturus, this Comet will move northward and pass near the handle of the Big Dipper between January 15 and 19. A finder chart for Comet Catalina is available here.
Western Slope Skies is produced by members of the Black Canyon Astronomical Society. This episode was written and recorded by Art Trevena.