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.

2026 May 6
The image shows two parellel rings of bright dots in the night sky. This is a composite image of the positions Saturn and Neptune traced in the sky from May 2025 to January 2026. The brighter ring in the foreground is Saturn, while the dimmer ring in the background is Neptune. Please see the explanation for more detailed information.

The Retrograde Dance of Saturn and Neptune
Image Credit & Copyright: Tunç Tezel (TWAN)
Text: Keighley Rockcliffe (NASA GSFC, UMBC CSST, CRESST II)

Explanation: What does it mean for Saturn and Neptune to be in retrograde? Featured is a composite of images taken over 34 nights from May 2025 to February 2026 tracing Saturn (brighter, foreground) and Neptune (dimmer, background). Over that time, the two planets exhibited retrograde motion, meaning they appeared to move backward in the sky. This apparent backwards motion occurs when Earth overtakes the slower outer planets as they orbit the Sun. Imagine the Solar System is a running track. Earth "runs" faster along the inside of the track compared to the outer planets. As Earth approaches, aligns, and then "laps" the outer planets, they change position from ahead to behind from the Earth's perspective. This perspective shift is what causes the outer planets to change position in the night sky. An animation corresponding to today’s image shows Saturn and Neptune’s months-long dance across the northern night sky. Saturn stepped from the Pisces constellation into Aquarius and back again while Neptune remained in Pisces. This is the closest Saturn and Neptune have been in the sky since their last conjunction in 1989.

Tomorrow's picture: spiralling into a supernova


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