The common question of whether stars are visible from space often arises from photographs showing astronauts or spacecraft against a seemingly starless black backdrop. The reality is nuanced, involving human vision and the technical considerations of space photography. Understanding these factors clarifies why the expected glittering expanse is not always apparent in images.
The Visibility of Stars from Space
Astronauts can see stars from space with greater clarity than from Earth. The absence of an atmosphere above Earth’s orbit removes the scattering and absorption of starlight, allowing for an unobstructed view. This clarity enables space telescopes, free from atmospheric interference, to provide detailed astronomical observations.
Stars are most visible to the human eye in space when ambient light is low. On the night side of Earth, away from direct sunlight or bright reflections, stars become readily apparent. Astronauts aboard the International Space Station (ISS) experience this night period sixteen times daily. During these periods of darkness, the full splendor of the cosmos, including the Milky Way, can be observed.
How the Human Eye Perceives Light in Orbit
The human eye adapts to prevailing light conditions through pupil constriction. In the intensely bright, unfiltered sunlight of space, or when looking at the brightly illuminated Earth, the pupil narrows significantly. This reduces the amount of light entering the eye, protecting the retina and allowing vision to focus on brighter elements.
This adaptation means that while sunlit objects appear distinct, dimmer objects like distant stars become less noticeable or even invisible. The eye’s sensitivity adjusts to the dominant light source, prioritizing intense light from the sun or sun-illuminated surfaces over faint starlight. For stars to be seen, the eye needs time to adapt to darkness, similar to adjusting to a dimly lit room on Earth.
Why Space Photography Often Excludes Stars
Space photographs often lack stars due to the technical requirements of capturing brightly lit subjects. Cameras are configured with short exposure times and small apertures to properly capture well-illuminated foregrounds like the spacecraft, astronauts, or Earth’s surface.
These settings prevent overexposure of the main subject but are insufficient to capture faint stars. Stars require much longer exposure times, often seconds or minutes, and wider apertures to register on a camera sensor. The absence of stars in many iconic space images is a deliberate photographic choice, ensuring the primary subject is clearly visible, not indicating their physical absence.