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Earth’s Shining Upper Atmosphere — From the Apollo Era to the Present

The image is composed of two images: on left, the Apollo 16 photo and on right, an image from the GOLD data visualization
Compare views of Earth’s shining ionosphere: the Apollo 16 photo taken in 1972 is at left, and an image from NASA’s GOLD data visualization is at right. The perspectives differ slightly because while the Apollo photo was taken from the Moon’s surface, GOLD images Earth’s ionosphere from geostationary orbit.
Credits: Apollo image: G. Carruthers (NRL) et al./Far UV Camera/NASA/Apollo 16; GOLD image: NASA/GOLD/Scientific Visualization Studio/Tom Bridgman/Joy Ng

In 1972, Apollo 16 astronauts John Young and Charles Duke stood on the Moon and looked back at Earth. From the lunar surface, they took a picture of Earth like none before: the first view of our planet in far ultraviolet light.

This picture highlights Earth’s ionosphere, a region of the upper atmosphere that is mostly invisible to our eyes — aside from aurora or airglow, if you’re in the right place at the right time —  but shines in ultraviolet, or UV, wavelengths of light. Named for the electrically charged ions that move about freely there, the ionosphere absorbs UV light from the Sun and re-emits it to space. The effect can be seen in this UV image. The Sun-facing side of Earth is bright. The rest of the planet, which is not receiving UV light from the Sun, remains dark, shrouded in night.

Attentive observers may notice three strips of UV emission that extend onto Earth’s night side. The two strips just above and below the equator are known as the Appleton Anomaly. They mark where Earth’s magnetic field interacts with the upper ionosphere to trigger dense fountains of uprising plasma. The southernmost strip is UV light from the aurora australis, or the Southern Lights.

The ionosphere over the Americas is shown transitioning from day to night. During the day, the ionosphere is brightly colored.
A visualization of GOLD data observing Earth’s ionosphere in ultraviolet light.
Credits: NASA’s Scientific Visualization Studio/Tom Bridgman/Joy Ng

Launched in 2018, NASA’s GOLD mission — short for Global-scale Observations of the Limb and Disk — is now one of our key tools for ionosphere observations, providing the first day-to-day weather measurements of the region. By measuring far UV light, GOLD tracks changes in the ionosphere’s ever-changing temperature, density and composition — enabling scientists to piece together the forces that shape conditions in a part of the atmosphere critical to many Earth-orbiting satellites and everyday technology, including the successful transmission of radio signals and GPS.

This visualization of GOLD data from March 2019 shows the transition from day to night, as well as the Appleton anomaly, which appears as two horizontal arcs of light that extend into night. The aurora can be seen at the top and bottom of Earth, also extending into night.

Two men stand on either side of a gold camera, which stands about three-quarters of their height.
Dr. George Carruthers, right, and William Conway, a project manager at the Naval Research Institute, examine the gold-plated ultraviolet camera/spectrograph that flew on the Apollo 16 mission. This camera would go on to capture the first image of Earth in ultraviolet light.
Credits: U.S. Naval Research Laboratory

By Miles Hatfield and Lina Tran
NASA’s Goddard Space Flight Center, Greenbelt, Md.