SDO Transit - September 2015

Released Monday, September 14, 2015
Updated Wednesday, September 16, 2015 at 2:38PM

ID: 11993

- Produced by:
- Genna Duberstein
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The Earth and moon photobomb SDO.

Watch this video on the NASAexplorer YouTube channel.

On Sept. 13, 2015, as NASA’s Solar Dynamics Observatory, or SDO, kept up its constant watch on the sun, its view was photobombed not once, but twice. Just as the moon came into SDO’s field of view on a path to cross the sun, Earth entered the picture, blocking SDO’s view completely. When SDO's orbit finally emerged from behind Earth, the moon was just completing its journey across the sun’s face.

Though SDO sees dozens of Earth eclipses and several lunar transits each year, this is the first time ever that the two have coincided.

SDO’s orbit usually gives us unobstructed views of the sun, but Earth’s revolution around the sun means that SDO’s orbit passes behind Earth twice each year, for two to three weeks at a time. During these phases, Earth blocks SDO’s view of the sun for anywhere from a few minutes to over an hour once each day.

Earth’s outline looks fuzzy, while the moon’s is crystal-clear. This is because—while the planet itself completely blocks the sun's light—Earth’s atmosphere is an incomplete barrier, blocking different amounts of light at different altitudes. However, the moon has no atmosphere, so during the transit we can see the crisp edges of the moon's horizon.

Image of the moon transiting across the sun, taken by SDO in 304 angstroms on September 13, 2015.

Credit: NASA/SDO

B-roll of the Earth and moon passing in front of SDO on September 13, 2015. SDO sees the sun in different wavelengths of the extreme ultra violet. The different wavelengths are color coded. Red is 304 angstroms and yellow is 171 angstroms.