0153 GMT September 18, 2019
The DSCOVR spacecraft, which was launched in February, has a camera that stares constantly at the sunlit face of the Earth.
The images are being used to track moving features such as clouds and dust storms, and monitor the climate, esciencenews.com reported.
But on Sept. 27, it was in just the right position to see the Moon go behind the Earth and into its shadow.
On the ground at this time, skywatchers would have observed the lunar body turn a shade of red.
It does this because some sunlight is still able to reach the Moon's surface after being filtered through the Earth's atmosphere.
"Our camera is normally centered on the Earth but we use the Moon for calibration," explained Jay Herman, the US space agency's (Nasa) lead investigator on DSCOVR's Epic camera system.
"That's what we were doing on this occasion. We were staring at the Moon and the Earth moved in front about four hours before the eclipse was seen on Earth. And that's because we were at an angular position, just to the side of the Sun-Earth line.
"The Earth is rotating as it goes by. It's kind of neat because you can watch the motion of the clouds."
Herman was speaking at the Fall Meeting of the American Geophysical Union in San Francisco — the largest annual gathering of Earth scientists.
The DSCOVR satellite is reported to be in excellent shape. In-space testing continues following the launch but science operations have started up nonetheless, and the AGU gathering is being used to report some early observations and results.
One of the satellite's objectives is to track cloud behavior. The different wavelength filters on Epic allow the camera to estimate cloud heights. This is important not just for monitoring weather systems, but also to understand the clouds' impact on the climate. Some help to cool the planet by reflecting sunlight back out into space; other clouds actually warm the Earth because they trap heat.
And in pursuing this work, Epic data has already observed some unexpected things, like the tracks of ships. These are not the wakes created by the vessels cutting through the ocean surface, but rather the clouds their exhaust system are seeding up above.
"It was very surprising for us that we could see them from one million miles, and they're even better seen if we use a longer wavelength because this gives you a strong contrast with the dark ocean," said Alexander Marshak, the DSCOVR deputy project scientist.