How do penumbra and umbra relate to eclipses?

Answer 1

The umbra is the portion of a shadow from within which none of the light source is visible.

The penumbra is the portion of a shadow from within which part but not all of the light source is visible.

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"Umbra" is the area of total shadow, while "penumbra" is the area of partial shadow.

Answer 2

Umbra is the opaque, darker part of the shadow. The penubra is the semi-opaque, lighter part of the shadow. Usually the penumbra is smaller the the ubmbra, but the solar eclipse on an exception. Both are parts of shadows.

Answer 3

Since the sun is a big source of light and not just a single point, there are places

behind the Earth where the Earth blocks part of the sun from your view but not all

of it. If you're anywhere in that space, you can see part of the sun, but not all of

it. If that's where you are, then you're in the "penumbra" of the Earth's shadow.

If you're lined up right in the middle, and close enough to the back side of the

Earth, then it blocks the whole sun from your view and you can't see any of it.

Then you're in the "umbra" of the Earth's shadow.

Answer 4

First, the Sun is enormous - almost a million miles across. It is a lot closer to us than other stars. So, we see it as much more than just a point if light.

If the Sun appeared to us as just a point of light we would only experience the "umbra" and not the "penumbra" in eclipses.

The umbra is a "full" shadow. The penumbra is only a partial shadow, where some light gets through.

The Earth and Moon are much smaller than the Sun.

The full shadows of the Moon and the Earth are cone-shaped and come to a point.

Consider a solar eclipse. The full shadow caused by the Moon, where the entire Sun is blocked (and before the "point"), is the umbra.

The partial shadow, where only a portion of the Sun is blocked, or out beyond the point, is the penumbra.

(The Latin prefix "pen" means partial or almost, such as "penultimate" for the "almost ultimate", sometimes used in a sporting context to refer to the semi-final round.)

A Solar eclipse: an observer in the umbra of the Moon's shadow sees a total eclipse.

An observer in the penumbra of the Moon's shadow sees a partial eclipse.

A Lunar eclipse: In a total eclipse, the whole of Moon moves through the umbra

of the Earth's shadow.

In a partial eclipse, just a part of the Moon moves through the umbra of the Earth's shadow.

Note: If the Moon moves through only the penumbra of the Earth's shadow, that's a "penumbral eclipse". Such an eclipse is hardly noticeable.

It can be classed as a type of partial eclipse.

(The link below divides penumbral eclipses into two types.)

See "related link" below for more details, with diagrams.

Answer 5

If the light source is fairly large, it will create a total shadow, when the entire light source is blocked, and partial shadow where only part of the light source is blocked. The "umbra" is the area of total shadow, while the "penumbra" is the area of partial shadow.

Answer 6

Since the sun is a big source of light and not just a single point, there are places behind the Earth where the Earth blocks part of the sun from your view but not all of it. If you're anywhere in that space, you can see part of the sun, but not all of it. If that's where you are, then you're in the "penumbra" of the Earth's shadow.

If you're lined up right in the middle, and close enough to the back side of the

Earth, then it blocks the whole sun from your view and you can't see any of it.

Then you're in the "umbra" of the Earth's shadow.

Answer 7

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the pig reacts to the ostrich and goes away

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Answer 8

The umbra is the darkest part of the shadow, in the middle, where none of the light source is visible.

The penumbra is the lighter, outer part of the shadow, where part of the light source but not all of it is visible.

Answer 9

The "umbra" is the complete shadow, while the prefix "pen" refers to something that is less than complete. So "penumbra" is the partial shadow.

You can do this as an experiment at home. Take three table lamps and line them up about two feet apart on one side of the room. Take a beach ball or a disk of cardboard (about a foot wide) to the other side of the room. There are three light sources. (In real life, the Sun is quite large, so three lamps gives us a good simulation.) Hold the beach ball or disk a couple of feet from the far wall. There will be an area of total shadow, where the direct rays of the lamps are blocked from all three lamps. This is the "umbra".

There will be a larger area of partial shadow, where the direct rays of one of the lamps can get to the wall, but the other two lamps are blocked; this is the "penumbra" or partial shadow.

If you move the disk away from the wall by a couple of feet, you'll get to a point where there is no umbra at all; the light from one lamp or the other reaches every part of the wall. That's the situation that we see in an annular eclipse, when the Moon is too far away to completely block the Sun's visible disk.

Answer 10

The word "umbra" means "shadow", and the prefix "pen-" means "almost, not complete". So the penumbra is the partial but not total shadow.

The Sun is a million miles in diameter, while the Earth is only 8000 miles or so in diameter. This means that the Earth's shadow (or the Moon's shadow) is like two cones, an outer cone of partial shadow and an inner cone of total shadow. The inner cone is the umbra; the outer cone is the penumbra.