# Presentation: 786163

## Solar Eclipses

**Solar Eclipses**

**Solar Eclipses**

## Solar eclipses: the big picture

- This drawing shows how the Sun, moon and Earth line up
- during a solar eclipse. The shadow area where you could see a _total_ eclipse is only 92 miles wide. If the entire Sun appears covered by the moon, this is called a total eclipse; if only part, then it is a partial eclipse.

- Click here to see an eclipse animation

## What do eclipses look like?

- •	Below you see an illustration of a total eclipse as seen from Earth. The entire process lasts only less than two hours, with the whole Sun blocked for up to eight minutes or less. Just during totality the corona seems to “glow” around the edges of the moon. Total eclipses occur somewhere on Earth only about once every 18 months.

## Why don’t eclipses happen every month?

- At first thought, it would seem that we should have an eclipse each month when the moon passes between the Sun and the Earth. Why not?
- The answer lies in the slight tilt (5o) of the Moon’s path in relation to the Earth’s path. It is usually above or below the direct sight line to the Sun.

- Sun-Earth line

- Moon’s tilted orbit

- Earth

## Total solar eclipse video

- This video of the June 21, 2001 eclipse seen in Africa shows the Sun just as it is going into totality

*Click on image to play video*

## Time series of an eclipse

- 	This series of photos shows a entire total solar eclipse, from beginning to end, in a series of pictures taken by the same camera over about a two hour period.

*Credit: Dennis Mammana*

## Partial eclipses

- 	From some places on the ground, viewers of eclipses only see part of the Sun covered by the Moon.  They see what we call a a partial eclipse.  Many more people see partial eclipses than total eclipses because the shadow’s path of the Moon for this is many times broader.

*Credit: Fred  Espenak*

## Eclipse shadows

- 	When the light passes through gaps between leaves of a tree, the shadows on the ground show little copies of the eclipse going on in the sky. In this eclipse, the moon did not quite cover all of the Sun, so you seen white rings.

- Credit: Ruth Benn

## Total eclipse photos

## Watching a total eclipse . . .

- •   As the crescent of light disappears, tiny specks of light are visible around the edge of the Sun. These specks of light are called Bailey's Beads and are the last rays of sunlight shining through the valleys on the edge of the Moon.
- •	Suddenly the sky is dark, but if you look toward the horizon you will see a reddish glow like a sunset. Once the Sun is totally eclipsed, the Sun's corona can be seen shining in all directions around the Moon. This is a spectacular sight because the only time the Sun's corona can be seen is during a total solar eclipse. Temperatures begin to fall.
- •	Also visible during a total solar eclipse are colorful lights from the Sun's chromosphere and solar prominences shooting out through the Sun's atmosphere. Without sunlight, bright stars and planets can be seen from the areas on earth in the Moon's shadow.

- “Bailey’s Beads” appearing just after totality

## Why do scientists care?

- Free from the blinding glare from the Sun itself, the corona that surrounds it is usually the prime target for the observations. So during an eclipse, expeditions go out to whatever sites seem most favorable, to capture what may be a once-in-a-lifetime observation of things that are otherwise hidden by the Sun’s brightness.
- A NASA spacecraft called SOHO creates a false eclipse with its coronograph instrument and observes the Sun all day, everyday.  Its observations can be compared with others on Earth during an eclipse to learn even more about them.

*An image of the Sun was placed on top of an eclipse image, which was centered on a coronagraph showing the extended corona (June 21, 2001)*

- Eclipse image: Williams College