This is an old revision of this page, as edited by Moverton (talk | contribs) at 08:38, 13 September 2004 (→Types of lunar eclipses: add Danjon numbers). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.
Revision as of 08:38, 13 September 2004 by Moverton (talk | contribs) (→Types of lunar eclipses: add Danjon numbers)(diff) ← Previous revision | Latest revision (diff) | Newer revision → (diff)An eclipse occurs whenever the Sun, Earth and Moon line up exactly. If this occurrence is at the time of a full moon where the Moon passes through the Earth's shadow, it is called a lunar eclipse. The type and length of lunar eclipse depends on the Moon's location relative to its orbital node.
Types of lunar eclipses
A penumbral eclipse occurs when the Moon only passes through the Earth's penumbra, the outer portion of the Earth's shadow. The penumbra does not cause a noticeable darkening of the Moon's surface.
A total lunar eclipse occurs when the Moon travels completely into the Earth's umbra, the dark inner portion of the shadow. The Moon's speed through the shadow is about one kilometer per second, and the total eclipse may last up to 102 minutes. However, the time between the Moon's first contact with the umbra and last contact, when it has completely exited the umbra, may be several hours. If only part of the Moon enters the umbra, it is called a partial lunar eclipse.
The Moon doesn't completely disappear as it passes through the umbra because of the refraction of sunlight by the Earth's atmosphere. The amount of refracted light depends on the amount of clouds or dust in the atmosphere blocking the light. This causes the Moon to glow with a coppery-red hue that varies from one eclipse to the next. The following scale was devised by Andrè Danjon for rating the overall darkness of lunar eclipses:
- 0. Very dark eclipse; Moon almost invisible, especially in midtonality
- 1. Dark eclipse; gray or brownish coloration; details distinguishable only with difficulty
- 2. Deep red or rust-colored eclipse, with a very dark central part in the umbra and the outer rim of the umbra relatively bright
- 3. Brick-red eclipse, usually with a bright or yellow rim to the umbra
- 4. Very bright copper-red or orange eclipse, with a bluish, very bright umbral rim
Because the Moon's orbit around the Earth is inclined 5° with respect to the orbit of the Earth around the Sun, lunar eclipses do not occur at every full moon. For an eclipse to occur, the Moon must be near its orbital node—the intersection of the orbital planes. Passing through the shadow at or very close to the node results in a total or partial eclipse.
Every year there are at least two lunar eclipses. If you know the date and time of an eclipse, you can predict the occurrence of other eclipses using eclipse cycles. Unlike a solar eclipse, which can only be viewed in a certain relatively small area of the world, a lunar eclipse may be viewed from anywhere on the night side of the Earth. If you were on the Moon's surface during a lunar eclipse you would witness a solar eclipse, with the Earth passing in front of the Sun.
Lunar eclipses in 2003
| There were two total lunar eclipses in 2003. The May eclipse grazed the northern edge of the earth's shadow, while the November eclipse grazed the southern edge.
All the light visible inside the umbral shadow is from light that is refracted around the earth's atmosphere. The color and darkness of the eclipse depends on clouds and other factors of the atmosphere. These images show the May eclipse was much darker than the one in November. |
Expected lunar eclipses 2003-2005
| Date | Type | Where Visible | Expected Duration |
|---|---|---|---|
| November 9, 2003 | Total | Americas, Europe, Africa, central Asia | 24 min |
| May 4, 2004 | Total | South America, Europe, Africa, Asia, Australia | 1 h 16 min |
| October 28, 2004 | Total | Americas, Europe, Africa, central Asia | 1 h 21 min |
| April 24, 2005 | Penumbral | Americas, Australia, Pacific, Eastern Asia | 4 h 10 min (duration of eclipse) |
| October 17, 2005 | Partial | Canada, Australia, Pacific, Asia | 58 min (duration of partial eclipse) |
History
Ancient Greek astronomers noticed that during lunar eclipses the edge of the shadow was always circular. They thus concluded that the Earth was spherical.
See also
External links
- Prediction
- Eclipse photos
- Fiction