This Tuesday (August 28) in the wee hours of the morning we should be able to witness a total eclipse of the Moon (lunar eclipse). There can be at any given location up to three lunar eclipses per year, but some years there may be none. There was one other total lunar eclipse in 2007 on March 3.

A lunar eclipse can only occur at Full Moon, and only if the Moon passes through some portion of the Earth's shadow. The shadow is actually composed of two cone-shaped components, one nested inside the other. The outer or penumbral shadow is a zone where the Earth blocks part but not all of the Sun's rays from reaching the Moon. The inner or umbral shadow is a region where the Earth blocks all direct sunlight from reaching the Moon. During a total lunar eclipse, the entire Moon passes through Earth's umbral shadow. and the vibrant range of colors the Moon can take on can be quite spectacular.

The reason that the Moon appears to change colors is that the dust in the Earth's atmosphere acts like a light prism and refracts, or bends, the light that strikes the Moon. It is impossible to predict exactly how dark the Moon will appear during totality. The colors can vary from dark gray or brown through a range of shades of red and bright orange. The color and brightness depend on the amount of dust in in Earth's atmosphere during the eclipse. (The same effect happens after a major volcanic eruption. So much dust is pumped into the atmosphere that it actually affects the colors we see in the sky during sunset. After a major eruption, we can have really beautiful sunsets for months afterwards.)

For those of us living in the Eastern Daylight Time Zone, here is the timetable for this eclipse:

Partial Eclipse Begins: 04:51 am
Total Eclipse Begins: 05:52 am
Mid-Eclipse: 06:37 am
Total Eclipse Ends: 07:22 am
Partial Eclipse Ends: 08:24 am

Unlike solar eclipses, lunar eclipses are completely safe to watch. You will need neither protective filters nor a telescope. You can watch the lunar eclipse with nothing more than your eyes. If you have a pair of binoculars, they will help magnify the view and will make the colors brighter and easier to see. A standard pair of 7x35 or 7x50 binoculars will work fine.

Of course, an eclipse of the Moon can be a tempting target to photograph. Fortunately lunar eclipse photography is easy provided that you have the right equipment and use it correctly. For an introductory guide on how to photograph an eclipse, see Lunar Eclipse Photography. To view photographs taken during previous lunar eclipses, be sure to visit Lunar Eclipse Gallery 1 and Lunar Eclipse Gallery 2.

If you would like to read additional information about lunar eclipses, you may wish to check out some websites. For information about lunar eclipses in general see NASA 's Lunar Eclipse Page. For information specific to this week's eclipse go on to Total Lunar Eclipse: August 28, 2007 . To use an astronomical application to find out when future eclipses will occur, visit the U.S. Naval Observatory's Lunar Eclipse Computer.

And do take a look at our library's collection of items about eclipses:

Celestial delights : the best astronomical events through 2010 by Francis Reddy and Greg Walz-Chojnacki.

Eclipse : the celestial phenomenon that changed the course of history by Duncan Steel.

Understanding the universe [videorecording : an introduction to astronomy produced by Tamara Stonebarger and directed by Robert Moss.

Glorious eclipses : their past, present, and future by Serge Brunier and Jean-Pierre Luminet; translated by Storm Dunlop.

Eclipse!: the what, where, when, why, and how guide to watching solar and lunar eclipses by Philip S. Harrington.

Nightwatch: a practical guide to viewing the universe by Terence Dickinson; illustrations by Victor Costanzo and Adolf Schaller ; featuring more than 70 photographs by amateur astronomers.

On Stonehenge by Fred Hoyle (argues that the purpose of Stonehenge was to predict the occurrence of eclipses, and reviews the resulting cultural implications).

Happy viewing to all you early risers. This day I intend to awake early also!