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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.

The picture shows the planet Neptune and its moon Triton, both in crescent phases, as captured by the passing Voyager 2 spacecraft in 1989. Please see the explanation for more detailed information.

Crescent Neptune and Triton

Explanation: Gliding silently through the outer Solar System , the Voyager 2 spacecraft camera captured Neptune and Triton together in crescent phase. The elegant picture of the ice-giant planet and its cloudy moon was taken from behind just after closest approach in 1989. It could not have been taken from Earth because Neptune never shows a crescent phase to sunward Earth. The unusual vantage point also robs Neptune of its familiar blue hue , as sunlight seen from here is scattered forward, and so is reddened like the setting Sun . Neptune is smaller but more massive than Uranus , has several dark rings , and emits more light than it receives from the Sun.

Date July 25, 2021
Credit Image Credit: NASA , Voyager 2
Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
A service of: ASD at NASA / GSFC,
NASA Science Activation & Michigan Tech. U.