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.

2025 May 5
The featured image shows a night sky over some choppy
water. The planet Venus shines high in the night sky, while a faint
Saturn in on the far right. The crescent Moon is visible near the
image center. A bright boat beacon is also visible on the right.
All of these objects are reflected as lines in the foreground
water.
Please see the explanation for more detailed information.

Planet Lines Across Water
Image Credit & Copyright: Jose Antonio Hervas

Explanation: What’s causing those lines? Objects in the sky sometimes appear reflected as lines across water — but why? If the water’s surface is smooth, then reflected objects would appear similarly -- as spots. But if the water is choppy, then there are many places where light from the object can reflect off the water and still come to you -- and so together form, typically, a line. The same effect is frequently seen for the Sun just before sunset and just after sunrise. Pictured about 10 days ago in Ibiza, Spain, images of the setting Moon, Venus (top), and Saturn (right, faint) were captured both directly and in line-reflected forms from the Mediterranean Sea. The other bright object on the right with a water-reflected line is a beacon on a rock to warn passing boats.

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