Template:POTD/2007-07-17

Picture of the day
Earth's atmosphere
An image of the top layers of Earth's atmosphere leading to outer space. Atmospheric gases scatter blue wavelengths of visible light more than other wavelengths, giving the Earth’s visible edge a blue halo. At higher and higher altitudes, the atmosphere becomes so thin that it essentially ceases to exist. Gradually, the atmospheric halo fades into the blackness of space.Photo credit: NASA Johnson Space Center