Full Lunar Eclipse Visible throughout Eastern United States on May 15

Late on the evening of Thursday, May 15, 2003, a total eclipse of the Moon will be visible, weather permitting, throughout most of North and South America beginning at about 10:00 p.m. EDT.

The eclipse officially starts at 9:05 p.m. EDT, as the Moon crosses into the penumbra of the Earth (the faint shadowy outline it casts in space). The eclipse won't really be noticeable until the Moon enters the full shadow of the Earth (the umbra), a few minutes after 10:00 p.m. EDT.

Totality, the point where the Moon is completely covered by Earth's shadow, begins at 11:14 p.m. Totality ends at 12:07 a.m. EDT (May 16) and the umbral phase of the eclipse will end at 1:17 a.m. EDT (May 16).

"A Lunar Eclipse is a great way for people to experience astronomy," said Lee Shapiro of the National Radio Astronomy Observatory in Charlottesville. "Unlike many objects in the night sky, the Moon is big and bright, so anyone can enjoy the event without having to invest in special equipment, or finding a spot far from normal city lights. Though, of course, a clear, dark night is still the best."

Total eclipses can only occur during a Full Moon, when the Moon moves into Earth's shadow. The Moon's orbital path usually takes it above or below the shadow cast by the Earth. A lunar eclipse occurs when the Sun, Earth, and Moon are almost perfectly in line (sometimes referred to as being in syzygy) -- with the Moon being on the opposite side of the Earth from the Sun.

This comparatively rare astronomical event should not be confused with watching the "phases" of the Moon (the Moon going from Full to New), which is caused by how much of the "illuminated" side of the Moon is visible from the Earth.

Rarely does the Moon disappear completely from view during a Lunar Eclipse. More often, some sunlight passes through the edges of Earth's atmosphere. This light is primarily red in color since the "blue" portion of the spectrum is more easily absorbed by Earth's atmosphere (think of the light from a red sky at sunset). This can give the Moon a red appearance. In fact, there is a scale that astronomers use to "rank" the brightness and color of the Moon during a Lunar Eclipse, it's called the Danjon Scale.

* L=4: Bright copper-red or orange umbra, with bluish rim.

* L=3: Brick-red umbra, with light gray or yellow rim.

* L=2: Deep red or rust-colored umbra, with dark center and brighter rim.

* L=1: Dark gray or brownish umbra. Difficult to see features.

* L=0: Very dark umbra. Moon itself difficult to see.

Size Comparison

To give you a feeling for the distances involved, imagine that your head were the Earth. The Moon would be about the size of your fist -- though your fist would have to be about 20 feet from your head for the scale to be right. On this scale, the Sun would be more than a mile away.

How rare is an eclipse? If you were to stand in one place, you will see a total Lunar Eclipse, on average, every two years. If you stood in the same place, you would see a total Solar Eclipse on average every 360 years.

Unlike Solar Eclipses, Lunar Eclipses are safe to view with the unaided eye, with binoculars, and even with telescopes. The difference is that the Sun is always dangerous to view, and during a Solar Eclipse that danger still exists. However, in the case of the Moon, the full Moon is safe to view, and that is not changed by the fact that it is going into the Earth's shadow.

For those in the Charlottesville area, the National Radio Astronomy Observatory (NRAO), the University of Virginia Astronomy Department, Ivy Creek Foundation, and the Charlottesville Astronomical Society will host a free public observing session of the lunar eclipse. The session will be held at the Ivy Creek Natural Area from 10:00 p.m. until 11:30 p.m. on Thursday, May 15.

As always, such optical observing sessions are weather dependent, and will not be held if the sky is completely cloudy or if it is raining.

The NRAO is a facility of the National Science Foundation, operated under a cooperate agreement by Associated Universities, Inc.

The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.