For most of July, observers have been catching a glimpse of the Comet NEOWISE in the night sky. Discovered on March 27 by NASA's Wide-field Infrared Survey Explorer space telescope, the comet is currently visible in the Northern Hemisphere just after sunset below the Ursa Major constellation. On clear nights, NEOWISE can be seen over the Dartmouth campus and around the Upper Valley.
Comets are composed of ice, rock, and dust, which is why they are often called "cosmic snowballs," according to Space.com. As these objects orbit the sun, they heat up and begin to emit tails, one made of dust and gas and another made of ions. In addition to the two common tails, NEOWISE has a third sodium tail, which has been observed only in bright comets like Hale-Bopp, the website says.
Skywatchers will be able to see NEOWISE until at least July 23, when it makes its closest approach to Earth. NASA says it won't return to our skies for another 6,800 years.