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# Thermosphere and Beyond

## The outer atmosphere is very thin; it contains the aurora.

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What Apollo Astronauts Saw

### What Apollo Astronauts Saw

Credit: Miles Orchinik
Source: http://miles-home.smugmug.com/Landscapes/Fire-in-the-sky/i-gbNddsx

We see twilight rays on Earth all the time, as the sun sets or rises. The Moon shouldn’t have twilight rays since it has virtually no atmosphere, but Apollo astronauts saw them. Scientists are sending a mission to the Moon to see why.

#### Why It Matters

Credit: Apollo 17 astronauts
Source: http://en.wikipedia.org/wiki/File:Apollo_17_twilight_ray_sketch.jpg

Twilight rays were sketched by the Apollo 17 astronauts at the Moon [Figure2]

• Astronauts on Apollo 8, 10, 15 and 17 saw twilight rays, even though scientists didn’t think they should exist on the Moon.
• The twilight rays on the Moon lasted only about 10 seconds.
• The Moon does have an atmosphere; it is only 10,000,000,000,000 times less dense than Earth’s.

#### Explore More

1. What gases are in the lunar atmosphere and what is the origin of each?
2. What might be present in the atmosphere that would increase its density enough to have twilight rays and where would this component come from?
3. What is an exosphere? What is the difference between exospheres on Earth and on the Moon?
4. What is the Lunar Atmosphere and Dust Environment Explorer looking for?
5. How will the mission end? Will scientists learn anything from the end?
6. How do the component parts of this story fit with how science is done by the scientific method?

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