From the Everett and Seattle Astronomical Societies, This Is IT's OVER

May 14, 2003030514.doc 1

From the Everett and Seattle Astronomical Societies, this is IT'S OVER

YOUR HEAD for the week of May 14, 2003, a look at what's up in the sky over

Puget Sound.

Well, OK, we're not in Miami but this week we do have a full lunar eclipse.

The lunar eclipse occurs during the evening of May 15th here in the Pacific

Northwest. The eclipse will already be underway by the time the moon rises in the Seattle area. An eclipse of the moon occurs when the Earth is exactly between the Moon and the Sun. An eclipse can only occur during a full moon.

During an eclipse, the Moon can be in the Earth's shadow for up to 1 ½ hours.

Totality for this eclipse is 53 minutes.

The shadow is actually composed of two cone-shaped parts, with one cone nested inside the other. The outer shadow, the penumbra, is an area where the

Earth blocks some, but not all of the Sun's rays. The inner shadow, the umbra, is an area where the Earth blocks all of the direct sunlight from reaching the Moon.

The Moon is never completely blacked out during a lunar eclipse. The reason for this is that sunlight is diffused through the Earth's atmosphere and lights the Moon with a dull glow that is about 1/10,000 of the brightness of a full moon. The darkness of the shadow varies due to the amount of dust, clouds and pollution suspended in the Earth's atmosphere. During this eclipse, the Moon will be in Libra, and will be lower in the ecliptic. Because of this, the eclipse may be darker as we will be looking at the Moon through more of the Earth's atmosphere.

The Moon will rise in the Seattle area on May 15th at 8:34 PM. The

penumbral eclipse begins at 6:05 PM. The partial eclipse begins at 7:02 PM and

the total eclipse begins at 8:14 PM. By the time the Moon rises in the Seattle

area it will be in total eclipse. Mid-eclipse occurs at 8:40 PM and the total eclipse

ends at 9:06 PM. The partial eclipse ends at 10:17 PM and the penumbral eclipse ends at 11:15 PM.

We may not be able to see totality due to the strong evening twilight. The best way to observe an eclipse is with binoculars or a low power telescope so that you can see the entire disk. Be sure to watch for subtle variations in the color of the shadow during the various phases of the eclipse. The color can range from bright orange to blood red to dark brown and (rarely) very dark gray.

A French astronomer, André Danjon (1890-1967), developed a 5 point

scale for evaluating the appearance and brightness of the Moon during a total

lunar eclipse. He developed his method by using a telescope in which a prism

split the image of the Moon into two identical side-by-side images. By adjusting a

diaphragm, he was able to dim one of the images until the sunlit portion had the

same apparent brightness as the earthlit portion on the unadjusted image.

Knowing the amount of the diaphragm adjustment, he was able to determine the

brightness of the Earthshine. This method is now known as the Danjon Scale. In

this scale, zero equals a barely visible Moon.

Danjon used 'L' values to quantify the sightings: L = 0 Very dark eclipse.

Moon almost invisible, especially at mid-totality.

L = 1 Dark Eclipse, gray or brownish in coloration. Details distinguishable only with difficulty.

L = 2 Deep red or rust-colored eclipse. Very dark central shadow, while outer edge of umbra is relatively bright.

L = 3 Brick-red eclipse. Umbral shadow usually has a bright or yellow rim.

L = 4 Very bright copper-red or orange eclipse. Umbral shadow has a bluish, very bright rim.

The assignment of an 'L' value to lunar eclipses is best done with the naked eye, binoculars or a small telescope near the time of mid-totality. It's also useful to examine the Moon's appearance just after the beginning and before the end of totality. The Moon is then near the edge of the shadow and provides an opportunity to assign an 'L' value to the outer umbra. In making any evaluations, you should record both the instrumentation and the time. Also note any variations in color and brightness in different parts of the umbra, as well as the apparent sharpness of the shadow's edge. Pay attention to the visibility of lunar features within the umbra. Notes and sketches made during the eclipse are invaluable in recalling details, events and impressions.

In addition to this eclipse, there are 3 more eclipses during 2003. On May

31, 2003 there will be an annular solar eclipse, another total lunar eclipse on

November 9, 2003, and we close out the year on eclipses with a total solar eclipse on November 23rd.

For more on this week's topic, set your browser to 'ItsOverYourHead.org'.

Our broadcast was written by Jim Ehrmin and engineered by Greg Donohue.

Until next time, this is ______and ______wishing you clear skies and good viewing!

REFERENCES:

http://www.skynewsmagazine.com/pages/lunareclipse.html