BLOOMINGTON — While Americans are going over the river and through the woods to grandmother’s house on Thanksgiving Day, a comet is making a close visit to the sun.

Comet ISON — named after the Russia-based International Scientific Optical Network that discovered it — will make its closest approach to the sun Thursday, coming within about 750,000 miles of the solar surface.

Once that close encounter is completed it could become visible to the naked eye in Central Illinois — if it survives.

That’s a big “if.”

“It could break apart. It could be vaporized,” said Carl Wenning, a member of the Twin City Astronomers who was director of the Illinois State University Planetarium from 1979 to 2000.

The comet is not only contending with the heat of the sun but also its gravitational forces, explained Daniel LaRocca, manager of Illinois Wesleyan University’s Mark Evans Observatory, who has been doing research on the comet’s rotational period.

“It’s unusual in that it’s a sun-grazing comet that we’ve known about for more than a year,” LaRocca said.

He said analysis of photos and other data from various sources, including the Hubble space telescope and a probe orbiting Mars, indicated ISON has a diameter of about 4 kilometers.

No one knows with certainty what will happen next.

“Comets are like cats,” Wenning said. “They have tails and they do exactly as they please.”

If all goes well — for the comet and for comet lovers — ISON should be visible in the eastern sky before sunrise starting this weekend, he said.

While it was visible in mid-November, Wenning said, “it’s so close to the sun now, it’s lost in the bright morn-ing twilight.”

Comet tails tend to grow bigger — and often brighter — while near the sun, then fade as they go farther away.

Initially, only the tail will be visible above the Central Illinois horizon at dawn, but the head should appear by Dec. 3 about an hour before sunrise, Wenning said.

Wenning recommends finding a place away from bright lights where the horizon is relatively free of obstruc-tions. He also suggests getting out at least an hour before sunrise and bringing a pair of binoculars to see more details.

For a while, ISON was being touted as “the comet of the century,” but that sort of talk has died down.

“I think, personally, it’s been over-hyped, but it could be spectacular,” LaRocca.

Wenning said, “It’s a neat little comet.”

And LaRocca, a 2013 IWU graduate, has enjoyed being involved with other astronomers studying ISON.

“It’s been nice how the community came together,” LaRocca said. “It’s been a great ride for me.”

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