A NOT-SO-SPOOKY ECLIPSE
Dr. Terry Goforth
Associate Professor of Physics, SWOSU
Saturday, November 8, skywatchers have a chance to observe the second lunar eclipse of 2003. Once again, the full moon will pass through Earth’s shadow and, for a brief time, appear much dimmer and possibly in shades of red, orange, or copper instead of its usual bright white.
The moonlight we see is simply sunlight that has reflected off the moon’s surface. When the moon is in the umbra, there is (almost) no sunlight to reflect, so the moon appears dark. What little sunlight leaks into the umbra is light that has been deflected by Earth’s atmosphere. This deflection primarily scatters red and orange light, causing the moon to take on the characteristic “angry” colors associated with a fully eclipsed moon. (This same color selection is what causes sunsets and sunrises to appear red or orange.)
The Earth’s umbra (the darkest part of its shadow) is shaped like an cone (with Earth at the fat end) and extends over a million miles into space. The moon, a mere 240 thousand miles away, fits easily into this shadow. If the moon passes through the center of the shadow, totality can last over an hour and a half. This time, the moon will simply graze the umbra near its south side, so the total portion of the eclipse will be relatively short, lasting only about 25 minutes. This proximity to the edge of the umbra also means the moon will likely be darker near its northern side and somewhat lighter near the southern edge. The exact color of the moon during totality depends on the amount of dust and moisture in Earth’s atmosphere at the time of the eclipse.
For viewers in Weatherford, moonrise will occur at 5:29 p.m. on Saturday. The partial phase of the eclipse (when only part of the moon is in the umbra) begins at 5:32 p.m. (8 Nov, 23:32 UT*), when the moon is still very low on the east-northeastern horizon. The moon will continue moving into the umbra as it rises. Totality (when the moon is completely inside the umbra) begins at 7:06 p.m. (9 Nov, 01:06 UT) At this time, the moon will be about 20° above the eastern horizon. Totality will end at 7:31 p.m. (9 Nov, 01:31 UT) as the moon begins to emerge from the umbra. The second partial phase of the eclipse (as the moon moves out of the umbra) will continue until 9:04 p.m. (9 Nov, 03:04 UT), by which time the moon will be about half-way up in the east-southeastern sky. (If you don’t live near Weatherford, the time of moonrise may be slightly different, but the eclipse times will be the same.)
Lunar eclipses are easy to observe. No special equipment is needed, and they happen right on time. All you’ll need are clear skies and a view of the eastern horizon. If you have binoculars or a telescope, it’s worth a look to see some details on the moon. There’s no danger in looking directly at the moon with your eyes, binoculars, or through telescopes. Unlike observing solar eclipses, the light is not bright enough to cause any damage. So take a look. Weather permitting, it will be a good show.
More information: There are many web sites and publications with information on this event. Try the the November 2003 issue of Sky & Telescope (skyandtelescope.com) or the November 2003 issue of Astronomy magazine (www.astronomy.com). NASA information and links can be found at science.nasa.gov/headlines/y2003/04nov_lunareclipse2.htm.