This Saturday morning -- June 26 -- beginning around 1017 UTC, take a look up in sky. If you’re in the central and western portions of the US and Canada, you have a good chance of seeing a partial lunar eclipse. Unfortunately, people in New England and Northeastern Canada will just miss the eclipse, as the Moon sets shortly before it begins. If you’re out camping, getting ready for Field Day to start, this is a great time to view a lunar phenomenon that only happens a few times a year.

A lunar eclipse occurs when the moon passes behind the Earth such that the Earth blocks the Sun’s rays from striking the Moon. This can occur only when the Sun, Earth and Moon are aligned exactly, or very closely so, with the Earth in the middle. Hence, there is always a full moon the night of a lunar eclipse.

According to NASA Science Editor Dr Tony Phillips, this lunar eclipse will be a “big one” for many residents of the USA. The eclipse begins at 3:17 AM PDT (1017 UTC) when the Moon enters the sunset-colored shadow of Earth. By 4:38 AM PDT (1138 UTC) -- the moment of greatest eclipse -- 54 percent of the Moon’s diameter will be covered. From beginning to end, the event will last almost three hours.

“Although the eclipse is only partial, it will be magnified in size and charm by the ‘Moon Illusion’ -- a result of the eclipse occurring close to the horizon from viewing sites in the USA,” Phillips said. “For reasons not fully understood by astronomers or psychologists, low-hanging Moons look unnaturally large when they beam through trees, buildings and other foreground objects. In fact, a low Moon is no wider than any other Moon -- cameras prove it -- but the human brain insists otherwise. Who are we to argue?”

The effect will be particularly strong in western and central parts of the USA and Canada where the Moon will be setting as the eclipse reaches maximum. Phillips advises observers to look low and to the west just before dawn. He notes that just because the Moon looks to be “extra size,” it’s just an illusion and in no way detracts from the beauty.

Halfway around the world, observers in India, Japan and parts of East Asia will experience the same phenomenon. They’ll see the eclipse on Saturday evening as the Moon is rising. The Moon Illusion will be fully active as Earth’s shadow sweeps across low-hanging lunar terrain. “It almost makes you feel sorry for people living on the dreamy islands of the South Pacific,” Phillips explained. “There, the eclipse takes place directly overhead, high in the midnight sky where the Moon Illusion does not work. That’s okay. A partial lunar eclipse is a beautiful thing all by itself.”

Click here for tips on how to best photograph a lunar eclipse.