Sky watchers will have their eyes peeled Wednesday night for a rare-ish celestial event: an “eclipse” of Mars. Weather or not Chicagoans will be able to view the show — pun intended — depends on the cloud cover.

If the evening is clear, look up shortly after 9 p.m. to see the full moon slide in front of Mars, obscuring the red planet until it emerges on the other side of the lunar disc an hour later.

The phenomenon is known as occultation, which in plain speak means “something passes in front of something else in the sky and blocks the view,” said Michelle Nichols, director of public observing at Adler Planetarium.

“You could call it an eclipse, they kind of mean the same thing,” Nichols said, though eclipse is usually reserved for events involving the moon, she added.

Occultations in general happen fairly often — think of all the times the moon passes in front of a star — it’s just that the temporary disappearance of an object no one can see or is paying attention to in the first place tends not to create much of a stir.

But there are only so many planets, Nichols said, and even fewer like Mars that are bright enough for an occultation to register as something to watch.

“The moon passes in front of Uranus and nobody notices,” said Nichols.

Plenty of these fly-bys occur during daylight hours and even when they do happen at night, they’re not visible everywhere on earth. Chicago is perfectly positioned for Wednesday’s event (with the caveat about the weather).

“I personally have never seen an occultation,” Nichols said. “I’ve never had the good fortune of it being clear or of looking at the right time.”

What she said should be particularly cool is the opportunity to get a sense of the moon’s movement through space, using Mars as a fixed point. 

The fact that anyone is talking about occultations at all is a lingering effect of the COVID-19 pandemic, when telescope sales went through the roof and people began turning to the skies for entertainment in the absence of anything else to do, Nichols said.

To meet demand, Adler launched its online Sky Observers Hangout series during the pandemic, and she’s been pleased to see people continuing to tune into the weekly YouTube sessions.

“It’s been really fun to ride that wave,” Nichols said.

She'll be hosting a virtual hangout Wednesday night to coincide with the occultation. The Adler will train its telescope on Mars “on the off chance we get even a second of a view,” Nichols said.

But no special equipment is needed to catch the show. 

With its distinctive orange glow, Mars is easy enough to spot, and will be even more so on Wednesday. Just pop outside at 9 p.m., locate the moon — to the southeast, about two-thirds up in the sky — and Mars will be the orange dot on its left, at roughly the 7 o’clock position. Then watch it disappear. 

The next opportunity for Chicagoans to catch such an event won’t come around until January 2025.

Contact Patty Wetli: @pattywetli | (773) 509-5623 |  [email protected]