Two Minute Read – Why Are Star Reflections in Water Elongated?

Why is the reflection of a full moon in the Snake River a stretched-out oval and not a round disk?

Why is the reflection of a full moon in the Snake River a stretched-out oval and not a round disk?

An interesting question came up during a recent NANPA webinar on “Chasing & Photographing the Aurora Borealis” presented by Carl Johnson.  Why is it that the reflections of stars, moon or sun in bodies of water always seem to have elongated shapes?  After all, when doing night photography, with a short enough shutter speed, the moon will be sharp and round; the stars will be tiny, sharp, points of light.  So why do they seem to stretch out when reflected in a lake, stream or pond?

The explanation has to do with the angle at which light from the stars hits the water and is reflected back at you and your camera.  Carl did the research and explains it well in Why the Long Reflection on his blog.

If you’re a NANPA member and you missed Carl’s Aurora webinar, you can watch and listen to a recording of this or any previous NANPA webinar in the Members’ Area of NANPA’s website.