A solar eclipse occurs when the Moon passes between the Sun and the Earth, casting its shadow on the Earth. The shadow comprises two concentric cones called the umbra and the penumbra. Observers on the Earth who are within the smaller, central umbra see the Sun completely blocked. Within the larger penumbra, the Sun is only partially blocked.

In this animation, the Earth, Moon, Sun, and shadow cones are viewed through a telescopic lens on a virtual camera located far behind the Earth. Long focal lengths like the one used here appear to compress the distance between near and far objects. Despite appearances, the geometry of the scene is correct. The Moon's umbra cone is roughly 30 Earth diameters long, barely enough to reach the Earth, while the Sun is almost 400 times farther away.

From this perspective, we see the night sides of both the Earth and the Moon. Solar eclipses can only occur during New Moon, when the entire Earth-facing side of the Moon is experiencing nighttime darkness.

Caption: A print-resolution still image showing the Earth, Moon, and Sun at 17:05:40 UTC during the August 21, 2017 eclipse. The image is 12 × 9 inches at 300 DPI.

More info:http://svs.gsfc.nasa.gov/4390

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NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission.

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