Can you see stars from the Moon? This question often arises because stars are absent from many iconic lunar photographs. The answer isn’t a simple yes or no. The visibility of stars from the Moon depends on several factors, including the Moon’s unique environment, the intensity of ambient light, and the capabilities of both cameras and the human eye.
A Sky Without Air
The primary difference between Earth’s sky and the Moon’s sky is the presence of an atmosphere. On Earth, our atmosphere, composed primarily of nitrogen and oxygen, scatters sunlight through a process known as Rayleigh scattering. This scattering creates the familiar blue sky and causes stars to twinkle.
In contrast, the Moon has virtually no atmosphere, only a very thin exosphere too sparse to scatter light. This means there are no particles to scatter or diffuse sunlight. Consequently, the lunar sky remains perpetually black, even during the lunar daytime. Sunlight travels directly to the surface, and away from the sun, the sky appears as the deep black of space.
The Brightness Challenge
Despite the black sky, seeing stars from the Moon presents a significant brightness challenge. During the lunar day, the sunlit lunar surface and illuminated objects, such as spacecraft or astronaut suits, are intensely bright. This extreme brightness comes from direct, unfiltered sunlight hitting the surface, unlike on Earth where light is diffused by the atmosphere. Our eyes and cameras struggle to simultaneously perceive these incredibly bright areas and the faint light from distant stars.
This is comparable to trying to see stars from Earth during the day; they are present, but the overwhelming brightness of the Sun and scattered atmospheric light make them invisible to the unaided eye. When a camera or eye adapts to capture the brightly lit lunar landscape, the dim starlight is too faint to register. Light reflecting off the Moon’s surface can be thousands of times brighter than starlight, effectively washing out the stars.
Camera Limitations and Human Eye Adaptation
Photographs from the Moon rarely show stars because cameras are set to capture the brightly lit lunar environment. To properly expose the sunlit landscape and astronauts, cameras use settings like fast shutter speeds and small apertures. These settings limit the light entering the camera, preventing overexposure of the bright foreground. However, these same settings prevent faint starlight from being collected sufficiently to appear in images. Stars are so dim they would require much longer exposure times, typically tens of seconds, which would completely overexpose the bright lunar surface.
The human eye, unlike a camera, can adapt to varying light levels. The pupil adjusts its size, dilating in low light and constricting in bright light. Beyond this, the retina’s photoreceptor cells, particularly rods, gradually increase their sensitivity in darkness, a process called dark adaptation. This adaptation can take several minutes to over an hour. Therefore, while astronauts might not casually see stars in the bright lunar day, their eyes could adapt to perceive them under specific conditions.
Astronaut Experiences with Star Visibility
Astronauts who visited the Moon confirmed that stars are visible from the lunar surface, but not under all circumstances. All Apollo missions landed during the lunar daytime, meaning the sun was always above the horizon. Under these bright, sunlit conditions, seeing stars with the unaided eye was challenging, similar to daytime viewing on Earth. Neil Armstrong and Buzz Aldrin did not recall seeing stars during their moonwalks.
However, astronauts could perceive stars if they were in shadow, such as behind the lunar module, and allowed their eyes sufficient time to dark-adapt. Some reported seeing brighter stars when shielding their eyes from direct sunlight or surface glare. Michael Collins, who orbited the Moon in the command module, saw a sky “awash with stars” when on the far side, away from direct sunlight. This confirms stars are present and visible when conditions allow the human eye to adjust to low starlight.