Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2023 September 17
A dark circle is seen in the image center. On both the
left and right of the circle are a series of bright half-rings.
Some parts of these bright half rings are dark, and the dark
areas look similar to mountains.
Please see the explanation for more detailed information.

Moon Mountains Magnified during Ring of Fire Eclipse
Credit & Copyright: Wang Letian (Eyes at Night)

Explanation: What are those dark streaks in this composite image of a solar eclipse? They are reversed shadows of mountains at the edge of the Moon. The center image, captured from Xiamen, China, has the Moon's center directly in front of the Sun's center. The Moon, though, was too far from the Earth to completely block the entire Sun. Light that streamed around the edges of the Moon is called a ring of fire. Images at each end of the sequence show sunlight that streamed through lunar valleys. As the Moon moved further in front of the Sun, left to right, only the higher peaks on the Moon's perimeter could block sunlight. Therefore, the dark streaks are projected, distorted, reversed, and magnified shadows of mountains at the Moon's edge. Bright areas are called Baily's Beads. Only people in a narrow swath across Earth's Eastern Hemisphere were able to view this full annular solar eclipse in 2020. Next month, though, a narrow swath crossing both North and South America will be exposed to the next annular solar eclipse. And next April, a total solar eclipse will be visible across North America.

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