Astronomy

What is an Eclipse



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There are two types of eclipses, solar eclipses and lunar eclipse.

First, what Is a Solar Eclipse?

Total solar eclipses occur very rarely, but if you happen to be on the correct side of the planet when they do, get ready to watch something incredible! Partial solar eclipses are a bit more common, but no less fascinating!

A solar eclipse happens when the moon passes in a direct line between the Sun and the Earth. The sun's light that normally illuminates Earth is temporarily blocked by the moon's shadow as it travels by.
There are only 2 eclipse seasons (the times when eclipses can occur) as the moon crosses the Earth's orbit only two times a year. But the moon has to be in the "new moon" phase during the eclipse season for solar eclipse to occur. Since the new moon coincides with one of the eclipse seasons rather seldom, solar eclipses are quite rare.

Types of Solar Eclipses

The moon's shadow has two parts: a central region and an outer region. You will see one of three types of solar eclipses, depending upon which part of the shadow passes your region of our planet: "Total", "Partial" and "Annular".

1. Total Solar Eclipse
During a "Total Solar Eclipse" the umbra (central region of the moon's shadow) passes over you and entire central portion of the sun is blocked out. All you can see is the sun's outer atmosphere, called the corona and it will seem as if it were nighttime.

2. Partial Solar Eclipse
During a "Partial Solar Eclipse" the penumbra (outer region of the moon's shadow) passes over you, and only part of the sun's surface is blocked out.
The sun's light will be just a little weaker than usual (dimmed), depending on how much of the sun's disc is visible.

3. Annular Solar Eclipse
During an "Annular Solar Eclipse" the moon is far enough away in its orbit that the umbra never reaches the Earth at all and all that is seen from the sun's disc is a small sliver of light that looks like a ring (the term "annular" means "of a ring").

Second, what Is a Lunar Eclipse?

A lunar eclipse occurs when a full moon passes through the Earth's shadow. An eclipse of the Moon (or lunar eclipse) can only happen when the moon is in its "Full Moon" phase, and only if the Moon passes through the Earth's shadow. Just like it is the case with solar eclipses, a lunar eclipse can only happen during the eclipse seasons. The Moon's orbit around Earth is actually tipped about 5 degrees to Earth's orbit around the Sun. This means that the Moon spends most of the time either above or below the plane of Earth's orbit, which is why we don't have a lunar eclipse every month and why solar eclipses are rather rare, as well!

Types of Lunar Eclipses

The Earth's shadow has two parts: a central region and an outer region. You will see one of three types of lunar eclipses, depending upon which part of the shadow passes your region of our planet:

1. Penumbral Lunar Eclipse

During a "Penumbral Lunar Eclipse" a part of the Moon passes through Earth's penumbral shadow and the Earth blocks only part of the Sun's rays from reaching the Moon. This is very subtle and quite difficult to observe.

2. Partial Lunar Eclipse
During a "Partial Lunar Eclipse" a part of the Moon passes through Earth's umbral shadow. This event can be seen with the naked eye.

3. Total Lunar Eclipse
During a "Total Lunar Eclipse" the entire Moon passes through Earth's umbral shadow and the Earth blocks all direct sunlight from reaching the Moon, which causes the Moon to take on a vibrant range of colors during the so-called "totality". Indirect sunlight still manages to reach and illuminate it. However, this sunlight must first pass deep through the Earth's atmosphere, which filters out most of the blue colored light. The remaining light is a deep red or orange in color. This is known to be a very captivating event.

Interesting Facts:
* On average, there are at least two solar eclipses a year. On average, however, a TOTAL solar eclipse on any spot on Earth happens only ONE time every 350 years!

* Solar eclipses usually only last for a couple of minutes, but lunar eclipses can last for one or two hours!

* The first astronomical event recorded in North America was a lunar eclipse on June 25, 1638.

* Lunar eclipses, most of which are visible to the naked eye, gave astronomers information about the solar system long before telescopes existed. As a matter of fact, Aristotle determined that the Earth is round by studying a lunar eclipse!

* If the Earth had no atmosphere, then the Moon would be completely black during a total eclipse.

To find out the next time you should be able to enjoy an eclipse go to:
http://sunearth.gsfc.nasa.gov/eclipse/SKYCAL/SKYCAL.html?cal=2007 or http://www.mreclipse.com

Happy observing!

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