This is an archived article that was published on in 2010, and information in the article may be outdated. It is provided only for personal research purposes and may not be reprinted.

A large, full moon will herald in the fall as it graces the skies on the autumnal equinox for the first time in nearly 20 years.

Today is the last day of summer, and as the sun sinks into the western horizon, the Harvest Moon will rise in the east, creating a 360-degree, summer-autumn twilight that is rarely seen, said Tony Phillips of Science@NASA.

The moon may appear much wider than normal due to the moon illusion that is still not understood by astronomers or psychologists.

"A Harvest Moon inflated by the moon illusion is simply gorgeous," Phillips said. "The view improves as the night wears on."

Autumn officially begins at 9:09 p.m. in Utah, and at that time the moon will be overhead with Jupiter just next to it.

"The two brightest objects in the night sky will be in spectacular conjunction to mark the change in seasons," Phillips said.

Typically, the Harvest Moon arrives within days or weeks of the autumnal equinox, but rarely does it align perfectly. The Harvest Moon of 2010 reaches its maximum illumination only six hours after the official start of fall. There hasn't been a comparable coincidence since Sept. 23, 1991, when the moon was brightest 10 hours from the equinox. Such an alignment won't happen again until 2029.