A green comet astronomers call Comet ZTF is visible in the northern night sky for the first time since the Ice Age.  And with the help of a telescope, you can see it too before it vanishes from the night for what might as well be forever.

Formerly known as C/2022 E3 (ZTF), this comet was named after the Zwicky Transient Facility in California where it was discovered by astronomers on March 2nd, 2022.  It was detected using highly sensitive cameras.

Comets are celestial bodies made of ice and dust that orbit the sun in elliptical orbits (or imperfect circles).  They spend most of their orbit out in the far reaches of the solar system before accelerating closer to the sun, and then are flung back out into space.  

The time taken for comets to complete an orbit is called a period.  Scientists classify comets in two categories: short period and long period comets.  Short period comets return to the sun in 200 years or less.  They don’t travel very far, and usually only make it to the Kuiper Belt (a region just beyond Neptune).

Comet ZTF is part of the latter class as its estimated period is around 50,000 years.  The last time it passed the Earth, Neanderthals would have been its observers.  Comets like this go beyond the Kuiper Belt and to the Oort Cloud (the most distant part of the solar system).  It takes a whole year for sunlight to reach this distant region.

As Comet ZTF accelerates towards the sun for the first time in millennia, heated up ice particles extend into a colorful dust tail, or “coma,” behind it.  Scientists predict that the green aura is caused when the sun’s UV radiation decays diatomic carbon (C2).  That causes the dicarbon to steam off its surface and produce the dust tail.  Green comets do exist in the solar system, but one this ancient is especially rare.

The best time to see Comet ZTF will be late January into early February.  According to NASA, February 1st is when it’s estimated to be closest to Earth.  Unfortunately, actually seeing the comet will be tricky.  Astronomers predict the comet will barely be above magnitude six (or barely visible) to us on earth.

Still, the best way to see Comet ZTF is to go somewhere with dark skies without ambient light from towns or cities.  Using a telescope is best, but binoculars could work on nights when it’s closest to earth.  According to Earthsky, the comet will be carving a path between the Boötes and Hercules constellations.  On January 30th, the comet will be closest to the North Star, or Polaris.  For more information, visit TheSkyLive for position updates.

On January 12th, the comet reached its perihelion, or closest point to the sun, and is already on its journey back out into the solar system.  And once its faint light leaves our skies, Comet ZTF won’t be returning for another 50,000 years.