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New View of Earth and Moon

July 27, 2016

As part of our unending series of moon updates,
here’s a wonderful item from NASA.

Imaging Camera (EPIC) camera and telescope, and the Earth - one million miles away. (NASA/NOAA)

Not photoshopped, but the far side of the moon, illuminated by the sun, as it crosses between the DSCOVR spacecraft’s Earth EPIC camera and telescope, and the Earth – one million miles away. (NASA/NOAA)

NASA explains:

A NASA camera aboard the Deep Space Climate Observatory (DSCOVR) satellite captured a unique view of the moon as it moved in front of the sunlit side of Earth last month. The series of test images shows the fully illuminated “dark side” of the moon that is never visible from Earth.

The images were captured by NASA’s Earth Polychromatic Imaging Camera (EPIC), a four megapixel CCD camera and telescope on the DSCOVR satellite orbiting 1 million miles from Earth. From its position between the sun and Earth, DSCOVR conducts its primary mission of real-time solar wind monitoring for the National Oceanic and Atmospheric Administration (NOAA).

EPIC maintains a constant view of the fully illuminated Earth as it rotates, providing scientific observations of ozone, vegetation, cloud height and aerosols in the atmosphere. Once EPIC begins regular observations next month, the camera will provide a series of Earth images allowing study of daily variations over the entire globe. About twice a year the camera will capture the moon and Earth together as the orbit of DSCOVR crosses the orbital plane of the moon.

Images taken between 3:50pm. and 8:45pm EDT, July 16, 2016, showing the moon moving over the Pacific Ocean near North America. The North Pole is in the upper left corner of the image, reflecting the orbital tilt of Earth from the vantage point of the spacecraft. (NASA/NOAA)

The far side of the moon was not seen until 1959 when the Soviet Luna 3 spacecraft returned the first images. Since then, several NASA missions have imaged the lunar far side in great detail. The same side of the moon always faces an earthbound observer because the moon is tidally locked* to Earth. That means its orbital period is the same as its rotation around its axis.

*Tidal Locking: Also called gravitational locking or captured rotation, this occurs when the gravitational gradient makes one hemisphere of a revolving astronomical body constantly face the partner body, an effect known as synchronous rotation. A tidally locked body takes just as long to rotate around its own axis as it does to revolve around its partner. For example, the same side of the Moon always faces the Earth. Usually, only the satellite is tidally locked to the larger body. However, if both the mass difference between the two bodies and the distance between them are relatively small, each may be tidally locked to the other, as is the case for Pluto and Charon. This effect is employed to stabilize some artificial satellites.
[posted by Chuck Almdale]

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