According to NASA, a supermoon can appear about 30 percent brighter and up to 14 percent larger than a typical full moon.
"When we're talking about something like the moon, the bigger the surface area, the more light it reflects back. So it's a little brighter that day," said John Gianforte, director of the University of New Hampshire Observatory.
"Looking at the moon with binoculars, a telescope, or just your naked eye is amazing. It just steals the show," he added.
The Harvest Moon will appear to have a reddish-orange glow as it rises just above the horizon in the east around 5:55 p.m., near sunset (6:16 p.m. in the Boston area) - making for some fantastic photographs. Peak illumination, when this supermoon officially turns "full," is at 11:48 p.m. EDT, and this year, the weather is going to cooperate for ultimate viewing, with clear skies forecast throughout the night.
"As the moon rises that night, it's going to lose that coloration because for every degree in altitude the moon rises, its light path through Earth's thick atmosphere is reduced," said Gianforte.
For those who will miss Monday night's peak brightness, the moon will still appear full through Thursday as it enters its waning gibbous phase. "It's like 97 percent illuminated, and it still looks full to most people," Gianforte noted.
This week is also a great time to see Saturn shining brightly in the night sky.
"September and October are the best times of the year to see Saturn because Earth and Saturn are at their minimum distance, and it's visible almost all night," Gianforte said. "It looks like a yellowish star, pretty close to the moon."
He said if you look to the south-southeast Monday night, Saturn will be the brightest object to the lower right of the moon.
"Binoculars will give you a great view of the moon, and you'll be able to see Saturn a little bit better, but you won't see the rings without enough magnification," he said. But any small backyard telescope will show the impressive rings.
In the Northern Hemisphere, the Harvest Moon is the full moon that occurs closest to the autumnal equinox (the start of astronomical autumn), which was Sept. 22.
It was named for the extra moonlight farmers depended on to work and harvest their summer crops late into the night. The Algonquins in the northeastern United States called it the Corn Moon, "as this was the time for gathering their main staple crops of corn, pumpkins, squash, beans, and wild rice," according to NASA.
The Harvest Moon's arrival can vary by two weeks, and when it falls in October, like this year, it takes the place of the Hunter's Moon. Between 1970 and 2050, there are 18 years when the Harvest Moon comes in October, according to Space.com. The last time was in 2020, and the next time will be in 2028.
But the Harvest Moon won't be the largest supermoon. You'll have to wait for the next supermoon on Nov. 5, called the Beaver Moon, which will be closer to Earth at around 225,829 miles. Then on Dec. 4, the third supermoon will peak at 6:14 p.m., the Cold Moon.
Supermoons happen three to four times a year and always appear in consecutive months.
Gianforte and other astronomers encourage people to seek out the night sky more often, and they'll be amazed at what they see.
"If you spend 20 minutes outside, you know, walking around the block or taking a trip around the backyard or to a schoolyard at night, you're going to see constellations, maybe an occasional pairing, a planet, the moon, maybe passing by a bright planet, it's always eye-catching and makes you maybe appreciate that kind of a nature walk."