Fifty-five years after our giant leap, scientists continue to learn about the Moon and Earth from our celestial neighbor. A recent image from the ISS captures the crescent Moon and Earth’s glow, providing insights into decreasing albedo and Earth’s climate trends highlighted by NASA’s CERES project.

Since NASA first landed humans on the moon with the Apollo 11 mission in 1969, we have continued to honor our closest celestial neighbor. Whether it’s for its role in solar eclipses, illuminating long winter nights, or the mysteries of its underside, the Moon inspires awe and wonder.

Earth’s glow and Moon’s perspective

An astronaut aboard the International Space Station captured the feeling of lunar wonder in this photo taken in May 2024. The image shows the Moon in its waxing crescent phase, with only a small sliver of sunlight visible on the right. The rest of the Moon, though much less brightly, is illuminated by the Sun’s light reflected off Earth; this phenomenon is called an aurora.

Below the Moon, Earth’s bright horizon, or limb, arcs across the bottom of the image. This perspective photograph offers a cross-section of the layers of the planet’s atmosphere, including the orange troposphere closest to the surface and the thicker, light blue stratosphere above it.

Climate information obtained from lunar observations

Scientists can learn about our home planet by studying the Moon. Among other things, it offers clues to how life on Earth emerged and what earthquakes were like in the planet’s early history. The Moon also helps scientists monitor Earth’s brightness, or albedo, through aurora.

Climatologists are interested in albedo because it is a major component of the Earth’s energy budget, the balance of energy entering and leaving the Earth system. Ice cover, cloud cover, air pollution, and land cover affect albedo, the amount of light the Earth reflects back to space.

According to a 2021 study, auroral observations by scientists at the Big Bear Solar Observatory between 1998 and 2017 indicate an overall decrease in albedo during this time period. The authors note that warming sea surface temperatures, particularly those reducing low-level, highly reflective cloud cover over the eastern Pacific Ocean, may have contributed to this trend.

Earth’s reflection off the Moon provides a seemingly elegant measure of albedo. But NASA scientists are using a range of satellite instruments combined with meteorological, aerosol and other data to create a more detailed, long-term record of Earth’s brightness. Since the 1990s, the CERES (Clouds and Earth’s Radiant Energy System) project has been measuring the amount of solar energy absorbed and reflected by Earth, the heat the planet radiates into space and the role of clouds in this process.

CERES found a decrease in Earth’s albedo in the first two decades of the 2000s and a doubling of Earth’s energy imbalance between 2004 and 2019, suggesting that the Earth system is gaining energy and therefore warming. A prime candidate for these trends is a decrease in low cloud cover, said CERES Principal Investigator Norman Loeb of NASA’s Langley Research Center. However, it is difficult to tease apart the causes of the changing cloudiness, including changes in sea surface temperature, short-term natural variability and aerosol pollution. “Right now, this is not a solved problem,” he said.

NASA’s lunar exploration continues

NASA’s interest in lunar exploration remains high 55 years after Apollo 11. Through the Artemis campaign, NASA will send astronauts to the lunar South Pole region, advancing scientific discovery and preparing humans for missions to Mars.