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 January 1
The featured image shows several streaks on a dark background
with a pale blue dot in one of the streaks.
Please see the explanation for more detailed information.

The Largest Rock in our Solar System
Image Credit: NASA, Voyager 1 spacecraft

Explanation: There, that dot on the right, that's the largest rock known in our Solar System. It is larger than every known asteroid, moon, and comet nucleus. It is larger than any other local rocky planet. This rock is so large its gravity makes it into a large ball that holds heavy gases near its surface. (It used to be the largest known rock of any type until the recent discoveries of large dense planets orbiting other stars.) The Voyager 1 spacecraft took the featured picture -- famously called Pale Blue Dot -- of this giant space rock in 1990 from the outer Solar System. Today, this rock starts another orbit around its parent star, for roughly the 5 billionth time, spinning over 350 times during each trip. Happy Gregorian Calendar New Year to all inhabitants of this rock we call Earth.

Tomorrow's picture: planets align


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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
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