Diagram of Umbra and Penumbra. During an eclipse, two shadows are cast. The first is called the umbra (UM bruh).

The second shadow is called the penumbra (pe NUM bruh). The penumbra gets larger as it goes away from the sun. Last Updated: Aug 7, 2017.In the picture of the Sun and a Moon, you can see that directly in front of the Moon is the umbra.

In fact, the southernmost part was much darker than in the image taken by the tablet. The entire Moon was in the umbra of the Earth for a little less than 5 minutes, hence the term 'total' eclipse, but it was just barely in the umbra (which is why the total phase lasted less than 5 minutes), so the northern part of the Moon was just barely covered by our shadow, and sunlight shining through the ring of air surrounding the body of the Earth lit up that part much more than the regions deeper in the shadow, making them look much darker. The best image I was able to get of the total lunar eclipse of using a Kindle Fire to take a 4-power image of the Moon.

At that place the Earth appears to be exactly the same size as the Sun and in exactly the same direction as the Sun, and just barely covers it completely. In the upper part of the penumbra the Earth is in front of the bottom of the Sun, but an observer could look over the top of the Earth and still see the top of the Sun while in the lower part of the penumbra the Earth is in front of the top of the Sun, but an observer could look under the bottom of the Earth and still see the bottom of the Sun.( not to scale objects are shown larger and closer together than in reality)The Earth's umbra is a cone-shaped region as large as the Earth at the center of the Earth, and gradually decreasing in size as you move away from the Earth until - at a distance of about a million miles, or four times the distance to the Moon - you reach the tip of the cone. Where they do not overlap is the Earth's penumbra (Latin for partial shadow), a region where part of the Sun is visible and part of it is blocked from view by the Earth. Where those overlap on the night side of the Earth is the Earth's umbra (Latin for shadow), a region where neither the top nor the bottom of the Sun can be seen (nor of course, any part in between). :-(As shown in the diagram below, two lines can be drawn from the bottom of the Sun past the Earth, to define a region where the Earth blocks any view of the bottom of the Sun and similarly, two lines can be drawn from the top of the Sun past the Earth, to define a region where the Earth blocks any view of the top of the Sun.

If it is positive but less than 1, part of the Moon enters the umbra but not all of it, and we have a partial lunar eclipse, as shown above, where the depth was 0.19, meaning that 19% of the Moon's diameter was inside the umbra at greatest depth (also the moment the image was taken). If the depth is negative none of the Moon enters the umbra, and we have a penumbral eclipse. The two shadow regions were appropriately darkened and labeled by image-processing software.Eclipses of the Moon can be differentiated by the depth of the eclipse, which represents the portion of the lunar diameter which is inside the umbra at greatest eclipse. That portion of the Moon covered by the umbra is lit only by light refracted through the Earth's atmosphere, and appears pitch black in comparison to that portion covered by the umbra, which is lit by part or most of the uneclipsed Sun.Where the Earth's shadow passes through empty space it is not visible but in this image, eclipse enthusiasts enjoying the view of the partially eclipsed Moon arranged themselves so that one of them, by holding a hoop just above the Moon was able to simulate the position of the umbra. (more to be added in the next iteration of this page)A whimsical look at the partial lunar eclipse of September 7, 2006(Laurent Laveder, PhotoAstronomique.net, apod060909)In a partial lunar eclipse the Moon crosses above or below the center of the Earth's shadow, so only a portion of its surface is covered by the central darker shadow or umbra, and the rest is covered only by the outer lighter shadow or penumbra. Since that part of the Moon receives no direct sunlight it is much darker than the region still outside the umbra, and casual examination makes it appear completely dark but once all of the Moon is inside the umbra (and the eclipse becomes total), the fact that some sunlight filters through the Earth's atmosphere and illuminates the eclipsed Moon becomes obvious, and the Moon takes on a ruddy hue characteristic of the ruddy hue of the setting or rising Sun.

Just inside the outer edge of the penumbra someone on the Moon would see the Earth just barely covering a small part of the Sun, so the Sun's light is hardly dimished while just outside the umbra someone on the Moon would see the Earth almost entirely covering the Sun, so the Sun's light is considerably diminished. Areas on the Moon that are very close to the umbra may become noticeably darker, but areas further away look essentially the same as at any other full moon.

Penumbra Moon Definition