For the first time in 50,000 years, the green comet is making a pass by Earth.

The comet, known as C/2022 E3 or Comet ZTF, will be closest to Earth late Thursday night. But the celestial body should still be visible for another week, growing ever more faint, given the right conditions.

Clear skies were expected Thursday night, but forecasters were calling for some nighttime clouds this weekend.

The comet will start to be visible around sunset and should be visible throughout the night, said Mobile Earth and Space Laboratory President Dimitri Klebe.

Klebe advises comet viewers to look north and use the Big Dipper as a reference point and look to the left of it. He said people should look about 40 or 50 degrees above the horizon and make sure there are no mountains or other objects blocking the view.

For best possible visibility, people should get out of town and away from lights that may take away from the comet’s brightness.

A telescope or binoculars are the best option for viewing. However, the comet will be faintly visible to the naked eye. Klebe said a telescope is the best option because it is more stable.

If the plan is to photograph the comet, phone cameras and DSLR cameras are the best option.

“The phone cameras are so good now and they have great stabilization,” he said.

Klebe recommends when shooting with a DSLR camera to use long exposure and a tripod for the best shot. He said it is likely that it won’t appear green to someone looking at it with the naked eye but when using a telescope or binoculars the color will show better.

A comet is often referred to by astronomers as “dirty snowballs” because they are primarily composed of ice and dirt. Generally, comets come from two different places in the solar system: the Kuiper belt or the Oort cloud.

The green comet comes from the Oort cloud, which is a spherical layer of icy objects that surrounds the solar system and is about 4.6 trillion miles from the sun.

Klebe said any time the comet’s orbit gets close to the sun it becomes visible because the sun causes the comet to evaporate, which is why it appears to be streaking across the sky.

“A lot of people think comets are streaking through the sky. But if you go from one night to the next, you’ll see that it moves in position to the stars, but in general, it hasn’t moved much from one day to the to the next,” he said.

He said people can see the streaks because of the dust and ice particles reflecting sunlight.

The coma, a hazy environment developed when the comet approaches the sun, is created as a result of the comet heating up and its ices turning to gas. Carbon-based molecules in the atmosphere are subjected to the sun’s UV radiation, which breaks them apart and removes their outer layers.

This generates a molecule called dicarbon, and because of the sun’s radiation, it reverts the molecule to its lowest energy state by emitting a photon, which for dicarbon is typically green.

tbrown@durangoherald.com