An unusual green comet, 46P/Wirtanen, will be visible in the night sky this month as it makes its closest approach to Earth in 20 years. It is one of the closest comet flybys of the last 70 years, and it may be possible to see the comet even without a telescope.
Named after astronomer Carl Wirtanen who discovered the comet in 1948, 46P/Wirtanen is 0.7 miles wide and completes an orbit around the sun every 5.4 years. This is fast for a comet, meaning that it is a “short-period comet” as opposed to a “long-period comet” which would have an orbital period of more than 200 years. Also, 46P/Wirtanen is described as a hyperactive comet because it has higher production rates than are typical for a comet of its size, making it relatively bright. In fact, 46P/Wirtanen was the brightest comet in the night sky last month, when it was photographed 2 light-minutes or 35 million kilometers away from Earth.
The image below was taken from an observatory near Mayhill, New Mexico, showing both the comet in the center of the image and the streak of a rocket body passing through the telescope’s field of vision beneath:
As 46P/Wirtanen comes closer, it should reach a level of brightness where it can be seen with the naked eye. With the best possible conditions, it may be visible in the sky for several weeks. In addition, the conditions for observing the comet from Earth are good, and scientists have predicted that the comet will be visible for most of the night of its closest approach as well as for many hours of the nights before and after the approach.
NASA has launched an observation campaign for the comet, working with the University of Maryland to invite both professional and amateur astronomers to track it as it moves through the night sky. A number of NASA observatories will be participating in the campaign, including NASA’s Goldstone Solar System Radar in California, the NASA Infrared Telescope Facility in Hawaii, the Hubble, Chandra, Swift, and Spitzer space telescopes, and an airborne observatory called the Stratospheric Observatory for Infrared Astronomy (SOFIA). NASA has also shared that they hope to gain more data about the comet from the Transiting Exoplanet Survey Satellite (TESS), as 46P/Wirtanen will pass through its observation field.