An Ode to the Moon: How NOAA Satellites Capture Earth’s Satellite

This article was originally published on September 30, 2020, but has been updated.

October 2020 offered a rare celestial treat—a full Harvest Moon on October 1st and a second full “Blue Moon” on Halloween night. While Blue Moons occur about every two or three years, the last time there was a Blue Moon on October 31st in all U.S. time zones was in 1944. 

NOAA’s satellites have a unique relationship with the moon-- Earth’s natural satellite. They use its reflected sunlight, gravitational pull, and orbital position to their advantage--and although not specifically designed to do so, NOAA satellites occasionally catch breathtaking glimpses of the Moon from their perspective in space.

Geostationary Glances

NOAA’s latest generation of Geostationary Operational Environmental Satellites, GOES-R, orbit at 22,300 miles above Earth. In this position, they orbit the Earth’s equator at the same speed the Earth rotates. This keeps both satellites in a fixed position in the sky, and from here, they use their Advanced Baseline Imager (ABI) to track the evolution and movement of clouds, weather systems, tropical cyclones, and other environmental phenomena.

This orbit is roughly one-tenth the average distance between the Earth and the Moon, and from this vantage point, the ABI instrument on both GOES East and GOES West regularly captures images of the Moon when it is near Earth’s limb, according to Joel McCorkel, GOES-R Project Scientist for NASA Goddard.

“Besides providing this captivating view, the signal from the Moon provides an independent reference of ABI’s radiometric stability for the reflected solar bands,” McCorkel said. “This signal is not directly used for operational image creation; however, it helps assess the quality and variability of the satellites’ operational calibration.”

VIIRS, the Visible Infrared Imaging Radiometer Suite, is one of the critical instruments onboard the JPSS satellites. It has a Day-Night Band (DNB) that is extremely sensitive to light sources. From hundreds of miles up, VIIRS can detect city lights, lightning, fires, and moonlight reflecting off clouds at night. With the Moon as its only light source, the DNB can also detect snow cover, smoke and dust motion, and ice movement in polar regions.

What’s more, a phenomenon called moon glint, where the satellite captures the reflected moonlight off bodies of water, can help pinpoint areas of light winds over water at night. The image below from the DNB shows how the calm water off the Texas coast acts like a mirror and reflects the bright moonlight back at the sensor.

The light visible from the Moon can also help reveal a tropical cyclone’s intensity after the Sun has set. Moonlight helps scientists determine high, cirrus clouds from low-level liquid clouds, enabling them to analyze a storm’s circulation. In this image, moonlight reflected off the clouds of Super Typhoon Wutip revealed mesovortices within the eye of the typhoon, indicating a very strong and well-organized storm.

From its position in space, EPIC provides a view of the far side of the Moon--which faces the Sun--that is never directly visible to us here on Earth. It also has captured the Moon’s shadow as it travels across the globe during solar eclipses, like the total solar eclipse that crossed the U.S. in 2017.