Stargazers were treated to a double dose of lunar spectacles in the night sky Tuesday.
A partial lunar eclipse coincided with a supermoon, when the full moon made its closest approach to Earth during its elliptical orbit. Because the full moon is a little bit closer to us than usual, this “supermoon” appeared larger and brighter than average. It’s also called a harvest moon since it’s the full moon closest to the autumn equinox, which is Sunday, and because of its association with harvesting this time of year.
To make the evening even more special, this supermoon underwent a partial lunar eclipse, which occurs when the Earth is positioned between the moon and the sun, casting the Earth’s shadow on the surface of the moon, dimming it.
“I think that lunar eclipses are the more interesting celestial phenomena,” said Jonathan Kemp, with Wellesley College’s Whitin Observatory. “A supermoon is a variety of a monthly full moon that appears slightly bigger in the night sky. However, a partial eclipse has both an irregularity in timing and observability as well as a uniqueness of how it evolves and appears to an observer over the course of the event.”
The next supermoon-lunar eclipse combo doesn’t take place until Oct. 8, 2033.
When will the supermoon appear?
This is the first of three supermoons this year. The next one will take place on Oct. 17.
During this first act, the supermoon will last for roughly three days through Thursday morning. The moon will reach perigee — its closest point in its elliptical orbit — at 9 a.m. EDT on Wednesday when it’s 222,007 miles away.
“At its closest point, the full moon can appear up to 14 percent bigger and 30 percent brighter,” Kemp said.
A supermoon does have an added effect on Earth: “Because the moon is in its closest approach to Earth, it can cause higher tides than usual,” according to NASA.
When will the partial lunar eclipse occur?
The best time to view the moon partially eclipsed will be from 10:12 p.m. to 11:16 p.m., EDT. During this partial eclipse, the umbra – the shadow’s darkest part – “takes a bite out” of just a fraction of the moon, according to NASA. The darkened area then eventually recedes, never reaching the totality phase.
Francine Jackson, an astronomer with Brown University’s Ladd Observatory in Providence, R.I., said the moon will begin entering the Earth’s outer, lighter shadow — the penumbra — at 8:41 p.m. “The penumbra is so dim in comparison to the umbra that very few persons notice any difference,” she said.
That “slight dimming of the moon will be difficult to notice until the top edge of the moon starts entering the full or primary shadow, the umbra, at 10:13 p.m. (EDT),” according to NASA. The eclipse will peak at 10:44 p.m. with only that top part of the moon plunged into darkness due to the shadow. The moon will then finish exiting the full shadow by 11:16 p.m., bringing Earth’s companion back to complete illumination by midnight.
“Since this partial eclipse only involves about 8.5% of the moon’s diameter entering the Earth’s shadow, Boston observers should look closely at the edge of the lunar disk to see this partial eclipse,” said Jonathan Kemp, with Wellesley College’s Whitin Observatory.
Experts said no binoculars are needed to view this eclipse as long as the weather cooperates.
Some clouds are expected tonight. Globe meteorologist Ken Mahan said your chances of catching both spectacles are best the farther north you are. Northern New England should see partly clear skies while partly to mostly cloudy skies are forecast for Southern New England.
While partial lunar eclipses happen at least twice a year, Kemp said, total lunar eclipses, in which the sun, Earth and moon are precisely aligned and the sunlight is completely blocked from reaching the moon, are quite rare. The next full one is next March, so stay tuned.
And if anyone wants to stay awake after tonight’s eclipse, Jackson said there’s an added bonus: the Neptune occultation.
“The moon will pass in front of Neptune at 4:13 a.m., Wednesday and Neptune will reappear on the other side of the moon at 4:33,” she said. “You do need binoculars to locate Neptune, but it will be close to the moon, hopefully fairly easy to find.”
Marianne Mizera can be reached at marianne.mizera@globe.com. Follow her @MareMizera.