Sunday, August 26, 2007

Eclipse of the Moon

On the morning of August 28, 2007, the full Moon will move through the Earth's shadow. This event is not rare, it is the second such event this year. This one, however, takes place at a time when the Moon is above the horizon for North and South America, the Pacific Ocean, and countries around the Pacific Rim. While the eclipse can be seen from beginning to end in the Pacific Ocean and the West coast of North America, the remainder of the locations mentioned above will at least see a part of it, while some of it occurs after the Moon sets (Eastern North America, all of South America), or before the Moon rises (Eastern Asia, Western Australia).

The various phenomena that occur on the Moon are seen simultaneously in all areas mentioned; the various locations have their own local time, of course. There is a worldwide standard time called Universal Time (UT), which is used to relate all world-wide phenomena and activities. For instance, the computer systems in the financial world have to be based on this time reference, in order to maintain the relationships of financial transactions. Other uses for an agreed-upon, common time reference are found in transportation and travel scheduling, this common reference is of importance to us here, in science, too - astronomy in this case. So here is the UT sequence of events for this Lunar Eclipse:

Penumbral eclipse begins (the first imperceptible darkening of the Moon) 7:53:39 UT
Partial eclipse begins (the main Earth shadow begins to cover the Moon) 8:51:16 UT
Total eclipse begins 9:52:22 UT
Greatest eclipse 10:37:22 UT
Total eclipse ends 11:22:24 UT
Partial eclipse ends 12:23:30 UT
Penumbral eclipse ends 13:21:01 UT

(all times taken from the Observers' Handbook of the Royal Astronomical Society of Canada, Toronto, Ontario, Canada)

UT is sometimes stated as Greenwich Mean Time (GMT). The various locations on Earth have their local time assigned based on their geographical "time zones". For North America, these time zones are 4 to 8 hours (East to West) "behind" UT. For instance, the Greatest eclipse for the West coast of North America, stated in Pacific Standard Time (PST) is 10:37:22 UT - 8 = 2:37:22 PST. An added complication is the use of daylight saving time. This adds an hour to the Standard Time in each time zone. So, for the above example, the Greatest eclipse occurs at 3:37:22 in the morning.

This event requires no telescope - the naked eye does a great job here. Any pair of binoculars will enhance the experience; in fact, for me, binoculars are the preferred means by which to view this event. Photography is relatively easy, but use a tripod and your optical zoom or zoom lenses to their maximum extent. The Moon appears surprisingly small in pictures taken with standard focal length lenses.

For an observer on the Moon, this event would look similar to this image of the planet Saturn, as seen from the Cassini probe - minus the rings.