Weve all seen a crescent moon.

But how many people can say theyve seen a crescent sun?

On Monday, area residents will be able to add themselves to that list, many for likely the first time ever, as a partial solar eclipse passes over New England for the first time in decades.

A total solar eclipse occurs when the moons path around the earth falls directly in line with the sun, blocking the natural sunlight and effectively turning day to night for a few short minutes.

The event itself isnt all that rare, Wheaton College Professor Anthony Houser said. But the moons position around the earth limits who can take part in the event when, creating the illusion that the astronomical phenomenon only comes about every once in a blue moon.

It happens about every two years, Houser, who runs the astronomy observatory at Wheaton, said. Its just rare that it happens locally. We havent had one on the contiguous United States since 1979. Whereas, I have foreign students from China, and they had two solar eclipses within two years not too long ago.

Its always happening somewhere. Were just fortunate its happening coast to coast here.

But, while the solar eclipse event is spanning across the entire United States for the first time in years, area residents wont be able to enjoy its full effect.

A total eclipse is visible when a location on earth is directly within the suns main shadow or umbra. If you happen to be within the wider shadow, called the penumbra, you see only a partial eclipse.

The path of totality this time around is limited to a stretch of the U.S. from Oregon to South Carolina based on the positioning of the solar spheres in the universe Monday.

But even when the moon is directly aligned between the earth and sun, it doesnt guarantee a total eclipse says amateur astronomer Roger Menard of The Astronomy Association of Southeastern New England.

Thats because the moons orbit isnt a circle, its an oval. That orbit means the moon is closer to the earth at some times than others.

When the moon is closest to the earth, its disc totally covers the sun. When its farther away its disc appears smaller and doesnt quite obscure the entire sun. Instead, the result is an annular eclipse in which the moon is encircled by a bright rim of sun sort of like the candy shell on an M & M.

So, knowledge that Mondays solar eclipse will see the astronomical event at its prime pure totality has left thousands across the U.S. vying for a spot along the eclipses trail.

But, area residents wont be left out.

Makeshift astronomers in our area can count on a second best, Houser said. About 65 percent of the sun will be covered by the moon, leaving residents with an unusual sight. The events peak takes place about 2:46 p.m.

When you look at the sun on a normal day, it doesnt look that big, about the size of a fingernail, Houser said. But at the height of the eclipse youll see the moon take a bite out of it. Weve all seen a crescent moon, but on Monday well see a crescent sun.

Attleboro will not see night, as will areas in the path of totality, but gradually as the eclipse takes place between 1:30 and 4 p.m., the outside will seem dimmer than usual, Houser said.

But because the event will draw watchful eyes to the sky, Houser and other astronomers are urging observers to take precautions in making sure theyre viewing the eclipse safely.

Instinctively, we dont look at the sun, Houser said. Its a natural reflex to look away from the bright sun or to blink to protect our eyes.

But those instincts go to the wayside for special events, and Houser said looking at the suns ultraviolet rays for an extended period of time, waiting for the eclipse to take place, could cause serious damage to ones retina even as far as partial blindness.

Its really important to observe safely, Houser said.

Regular sunglasses dont make the cut.

Special eclipse glasses can be found online or in stores although most vendors have struggled to keep up with demand in recent weeks. After fake glasses were discovered on the online market, NASA and the American Astronomical Society have endorsed brands with sufficient protection and urge viewers to buy from those vendors directly.

If you have proper glasses, when you put them on during the day it should be very dark, Houser said. You should see nothing.

But if you cant get your hands on eclipse glasses, Houser said theres other ways to view safely. NASA has compiled a list of techniques to view the eclipse indirectly on its website, and will also be streaming the eclipse live.

And, area astronomers and recreation facilities have committed to viewing parties, where eclipse glasses will be available to share.

Wheatons observatory deck will be open, and Houser said about six telescopes with safety filters will be available for those who want an even closer look at the sun.

In Foxboro, Troop 7 Boy Scouts will join the recreation department in hosting a special viewing party at Booth Playground from 12:30 to 4 p.m. Eclipse glasses will be on sale for $5.

And Recreation Director Debbie Giardino went to extra lengths to make sure no one will be without. Her department and the Boy Scouts will have 450 pairs of glasses on hand.

I didnt want to run out of glasses and have people miss the experience or put themselves in danger, Giardino said. If theres extra, theres extra.

Giardino said the event will be a party complete with food and a live stream of the total eclipse on a TV nearby.

She heard about plans of the gathering from the Boy Scouts, who will earn a badge from the event, and joined forces to make the event an experience all of Foxboro can enjoy.

We have the mechanics: The building, the wherewithal, the staff, all of the amenities that they were looking for, she said. But this was their idea from the start.

I think its a great community event. This is what we do. I hope families will come and made a day out of it. Its the end of summer and lifes too short not to enjoy an event that last took place 38 years ago.

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A crescent sun: Solar eclipse to mark astronomy event of the decade, even in New England - The Sun Chronicle