The moon will stage a rare triple show early Wednesday when a blue supermoon combines with a total lunar eclipse that will be visible from western North America to eastern Asia.
The overlap of a blue moon – the second full moon in a calendar month – with a lunar eclipse while the moon is at its closest approach to Earth is the first such celestial trifecta since 1982, said Noah Petro, a research scientist at NASA's Goddard Space Flight Center outside Washington.
"Just having these three things simultaneously occur is unusual," Petro said. "A blue moon is not extremely rare, but it's a nice coincidence that it happens in conjunction with these other two."
The moon will reach its fullest at 4:27 a.m. Wednesday Alaska time, just minutes before the peak eclipse.
A blue moon normally occurs about every 2-1/2 years. This month's first full moon was Jan. 1.
The blue moon also will be a "supermoon," which occurs when it is at or near its closest point to Earth, or perigee. A supermoon is about 14 percent brighter than usual, NASA says.
Wednesday's moon will be the second closest of 2018 after the one on Jan. 1.
The lunar eclipse, which takes place when the moon passes through Earth's shadow, will last almost 3 1/2 hours. In Anchorage, it will start at 2:48 a.m. Alaska time, hours after moonrise, and peak at 4:29 a.m. well before moonset.
"I'd mention that the moon will be high in the southwestern sky during the eclipse," said University of Alaska Anchorage astronomer Travis Rector. "It can be a little hard to find when it is in totality. "
The Anchorage weather forecast was calling for a cold and mostly clear night, with light winds.
The total eclipse will be visible from the western United States and Canada across the Pacific Ocean to most of Australia and China, as well as northern polar regions. The eclipse will give the moon a reddish color known as a blood moon.
"I'm calling it the purple eclipse because it combines the blue moon and a red eclipse," Rich Talcott, a senior editor at Astronomy magazine, said.
Petro said the eclipse is also a scientific opportunity for researchers in Hawaii, who will study what happens to the moon's surface when it quickly drops from 212 degrees F. in sunlight to minus 279 degrees in darkness.
The speed of cooling can show what the surface is made of, such as rock or dust, he said.
Reuters and the Anchorage Daily News contributed to this article.