A rare green comet which hasn’t been visible since the Stone Age is passing by Earth this week at a distance of 26 million miles. 

While comets aren’t an extremely rare sight, this one has several attributes that make it unique. 

The comet, named C/2022 E3 (ZTF), has a distinctly long orbital period — the time it takes for an object to orbit around the sun — tens of thousands of years, specifically. 

“It was last visible on Earth around 50,000 years ago,” physics and robotics teacher Stephen Hine said. “Neanderthals still existed on Earth at that point.”

Most comets we observe don’t have such lengthy orbit periods. Halley’s Comet, for example, has a smaller orbital period of just 75 years. 

This makes it an exceptional opportunity for people to witness C/2022 E3 (ZTF). It might also be the last time it’ll be observed by humans, as gravity may cause the comet to gain high speed and leave the solar system before it comes our way again. 

The best chance to spot the comet with the naked eye is tonight or tomorrow in the early morning in an area without light pollution or clouds.  You can find it by facing north, and looking 45 degrees up. The comet looks like a green blur, and you may be able to see the tail. 

The comet can also be seen until Friday, February 24 at the Foothill College Observatory’s Friday night viewings from 9 p.m. to 11 p.m. In addition, several livestreams are available online to observe its passing.