A partial lunar eclipse will darken and redden the moon late Thursday into early Friday, with the Earth's shadow covering more than 90% of the lunar disk at its peak, according to Jon Bell, Professor of Astronomy at Indian River State College and director of the college's Hallstrom Planetarium.
Bell said the moon will begin visibly dimming shortly after 10:30 p.m. Thursday, August 27, as the Earth's shadow starts to creep across its surface.
"The first bite that you see taken out of the moon by the Earth's shadow will occur shortly after 10:30, about 10:33 p.m. that evening," Bell said.
The shadow will continue to spread until maximum eclipse at 12:12 a.m. Friday, August 28. Because the alignment falls just short of a total eclipse, a sliver of the moon's upper limb will remain lit by direct sunlight even at the peak.
"It's not a total eclipse, so there'll be a little bit of the moon up on the upper limb of it will be still in daylight," Bell said. "The Earth's shadow won't reach there, but it'll be over 90 percent covered." The event will wind down by around 1 a.m., Bell said.
Even though the Earth's shadow blocks most direct sunlight from reaching the moon, some light still bends around the planet and colors the lunar surface.
Bell explained that sunlight passing through Earth's atmosphere near the twilight zone — where sunrises and sunsets are occurring — gets filtered so that red wavelengths pass through most easily, then reach the moon.
"The sky is filtering through all the light, the red goes out into space, hits the moon, and comes back to us," Bell said. He added that the moon will likely take on "a kind of almost a brick red or cherry red or kind of an orangey color" during the eclipse.
Bell recommended finding a spot with a clear, unobstructed view of the sky, away from streetlights, headlights and other bright sources.
"You just need a clear view of the sky and preferably as few streetlights as possible," he said, adding that clouds are the only real obstacle. "If it's cloudy that night, then the event will be eclipsed by clouds."
He suggested viewers settle in comfortably and safely away from traffic — a lounge chair, he said, works well for taking in the full moon before and during the eclipse.
Unlike a solar eclipse, Bell noted, there's no eye-safety concern with watching a lunar eclipse.
The Hallstrom Planetarium, located at 3209 Virginia Avenue in Fort Pierce, will host a free open house Thursday night from 9 p.m. until just after midnight, giving the public a chance to view the event through telescopes at no charge.
After Thursday's event, Bell said the next lunar eclipse won't arrive until February 20 — a penumbral eclipse, a fainter type in which the moon passes only through Earth's outer, lighter shadow rather than its dark inner shadow.
Bell also noted that the shape of Earth's shadow on the moon offers a simple demonstration of basic planetary science: the shadow is always round, showing Earth is a sphere, and its curve is roughly twice the size of the moon's limb, indicating Earth is larger than the moon.
"Some really cool science you can get, very, very, very elegant, but basic kind of observations can tell you a lot about what's going on out there in space and on Earth," Bell said.