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Space Station Science

Picture of the Day

Squashed Moon

April 16, 2003

Explanation: Aren't full Moons supposed to be round? This one wasn't.
Pictured here is a view of the full Moon seen through the Destiny Lab
window of the International Space Station on Jan. 18, 2003. The faint
blue glow below and around the Moon is Earth's atmosphere--and the
reason why the Moon appears strangely squashed. 

Atmospheric optics expert Les Cowley explains: "The Moon is flattened
by atmospheric refraction. Moonlight enters the atmosphere and then
leaves again, a path length twice that of moonrises seen from Earth's
surface. The atmospheric lens pushes the lower limb upwards to create
the flattened shape." Such refraction also causes stars photographed
through the upper atmosphere to look like meteors. 

The first examples of squashed Moons seen from Earth orbit were
recorded by astronauts onboard Skylab. They're also visible from
high-flying airplanes. The distortion is less if you're watching from
Earth's surface, but flattened Moons can be seen from the ground,
too. Try looking tonight, April 16th. Go out around local sunset and
look eastward for the rising full Moon. Low-hanging Moons often seem
swollen and colorful; catch one low enough and it might seem squashed
as well. 

Editor's note: Don Pettit took a second picture of the Moon on
January 18th. It was about 2o higher above the atmosphere and
appeared reassuringly round. 
 
Credits & Contacts
Author: Dr. Tony Phillips 
Responsible NASA official: Ron Koczor
Production Editor: Dr. Tony Phillips 
Curator: Bryan Walls 
Media Relations: Catherine Watson

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