Lunar Eclipse

In the early hours of Monday October 17th the full Moon will just graze the Earth's shadow, an event known as a partial lunar eclipse. While this won't be as dramatic as a total lunar eclipse, this Moon will look fairly different from a typical full Moon at 2 am that morning.


A lunar eclipse occurs when the Moon's orbit takes it through the shadow cast by the Earth. The eclipse is total if the Moon is completely shaded by the Earth, and partial if only part of it is shaded.

Path of Moon through Earth's shadow (Sky and Telescope)
Path of the Moon through the Earth's shadow. Objects within the umbra are completely shaded from the Sun; objects within the penumbra are partly shaded from the Sun. All times shown are Universal Time; to convert to local time, subtract 10 hours. Diagram from The October 17th Partial Lunar Eclipse (Sky and Telescope)

This diagram shows the Moon's path through the Earth's shadow on 10/17/05. The shadow has two parts. Within the umbra the Sun is completely hidden by the Earth, while within the penumbra only part of the Sun is hidden. As you can see, the Moon passes entirely within the penumbra but barely touches the umbra; thus we have a very shallow partial lunar eclipse.

This eclipse occurs early Monday morning; the edge of the Moon enters the umbra at 01:34 HT and exits the umbra at 02:32 HT. The Moon is deepest within the umbra at 02:03 HT. Between about 01:00 HT and 03:00 HT you may be able to see that the Moon is not fully illuminated; one side will appear brighter than the other due to partial shading within the penumbra.


Roberto H. Méndez (mendez@ifa.hawaii.edu)
Last modified: October 13, 2005
http://www.ifa.hawaii.edu/~mendez/ASTRO110LAB05/lunareclipse.html
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Lunar Eclipse: Worksheet

Fall 2005 ASTR 110L, Sec. 3 Name: ________________

This eclipse occurs at an inconvenient time, so this observation is extra credit. You'll get some credit even if you can only observe for a short time; mid-eclipse (about 2 am) should be the most interesting, but any observation is better than none! If clouds interfere, see if they drift away before giving up.

Use these charts of the full Moon to sketch the appearance of the Earth's shadow at different times. You will probably find a pencil useful to darken the part in shadow. Try to make a sketch as soon as you can see that one side of the Moon is shaded. Use binoculars to watch as the Moon enters the umbra (dark core of the shadow) at 01:34 HT, and make another sketch as soon as you see it. Make another sketch when the Moon is deepest within the shadow at 02:03 HT. Is the darkest part of the Moon completely black, or can you still see it? Do you notice any color to the shadow? Make yet another sketch just before the Moon exits the umbra at 02:32 HT. Finally, make a sketch after the Moon exits the umbra.

full moon chart
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full moon chart
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full moon chart
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full moon chart
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full moon chart
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Optional: Bang on pots and pans, set off firecrackers, and make lots of noise during the eclipse. When your neighbors call the cops, tell them you are scaring away the dragon which is eating the Moon.