October's full supermoon, comet predicted for skies over Philadelphia this week

In what has been quite a week for night sky connoisseurs, the promised comet, a fragment of our solar system's origins, has appeared in the western sky after sunset and appears to remain in sight for at least the next few days.

And it's about to share space with a “supermoon” rising on the opposite side of the sky, appearing significantly brighter and larger than the average full moon as it marks the closest approach of the year.

While you should be able to see the moon with the naked eye without any problem, comet C/2023 A3 Tsuchinshan-ATLAS may require a little more effort, which its fans say would be worth the effort.

In real life, the cometary materials may seem like a prosaic mix of rock and ice, but “these are the original building blocks of the solar system,” says Edward Sion, a professor of astronomy and astrophysics at Villanova University. Plus, this thing only appears every 80,000 years.

Where can I see the comet and how long will it be visible?

Clouds and light interference permitting, the comet will be visible almost due west after sunset Wednesday evening, at an angle of about 16 degrees above the horizon, NASA says.

As the Earth rotates, the comet slowly sinks toward the southwest, said Derrick Pitts, an astronomer at the Franklin Institute. He recommends viewing it with binoculars, even though it is visible to the naked eye.

“Comets look even brighter through binoculars or a small telescope,” agreed Bennett A. Maruca, a professor of astronomy and physics at the University of Delaware. “The gas and dust surrounding comets give them a 'fuzzy' appearance. In fact, the word comet is derived from the Latin word for “hairy.”

While the show is expected to last several days and the comet will rise higher each night, it will also decrease in brightness, Pitts said.

“By the end of the month it will drop below naked eye visibility,” he said.

About the supermoon

Unlike the comet, you won't have to wait 80,000 years for another chance to see the full moon, but this one will be extraordinary.

It is sometimes called the “Hunter’s Moon”. As for why, let's just say that back in the day you didn't want to be a deer out enjoying the moonlight.

The point of fullness will occur at 7:26 a.m. on Thursday, but only a celestial nitpicker could tell the difference between what peaks at 96.5% fullness on Tuesday evening and what peaks at 99.6% fullness on Wednesday, and recognize this 100% moment. The moon will be large and powerful on the horizon at 5:00 p.m. on Tuesday and 5:51 p.m. on Wednesday.

And since the moon and sun rock on a seesaw, the moon rises higher and higher while the sun sinks lower in the sky as winter approaches.

It will be about 30% brighter than when the full moon occurs at apogee – when it is furthest away – and 20% brighter than “typical,” said Karen Masters, a professor of astronomy and physics at Haverford College.

Granted, it's not an addition to the Northern Lights that electrified the skies over parts of the region Thursday evening, “but the moon is always beautiful,” she said.

And while no terrestrial solar flares or opportunities for auroras are expected in the near future, “the sun should remain active for a little longer,” Masters said, “so hopefully another one soon.”