This view of Earth rising over the Moon’s horizon was taken from the Apollo 11 spacecraft. Credit score: NASA.
Why do footage of Earth taken from the Moon present a black sky with no stars? Can the celebrities solely be seen with an environment?
Farris W. Bruce
Hesperia, California
The straightforward reply to your query is the digital camera settings used to take most pictures from the Moon weren’t designed to seize stars.
Apollo astronauts used movie cameras, so to know the reply, we have to clarify somewhat bit about how digital camera publicity works. Movie is a light-sensitive emulsion over plastic. When that plastic is uncovered to mild by way of the digital camera’s lens, a chemical change produces a adverse picture of no matter is photographed.
However the quantity of sunshine isn’t all the time the identical. A photographer has to contemplate the lens aperture and shutter velocity, each of which management how a lot mild hits the movie. A smaller aperture means much less mild, as does a sooner shutter velocity. It’s virtually like how your pupil constricts on a vivid day and dilates at night time: Your eye mechanically adjusts your aperture as a way to see in several situations.
A photographer additionally has to contemplate an important a part of the {photograph} earlier than setting aperture and shutter velocity. Typically talking, the brighter the goal object, the smaller the aperture and the sooner the shutter; in any other case, an excessive amount of mild will hit the movie, and the picture might be dominated by a washed-out, overexposed focus.
Associated: Do you’ve a space-related query? Ask Astro right here.
Let’s say you’re Neil Armstrong photographing Buzz Aldrin throughout a vivid lunar day. Buzz (in his spacesuit) and the lunar floor are going to be the brightest objects in your shot. So for him to be seen, you need to select a quick shutter velocity and a smaller aperture. The result’s a transparent picture of Buzz, however different mild sources, like the celebrities, are too dim to depart an impression on the movie.
As a result of an important issues the astronauts photographed have been one another and the Moon’s floor, their cameras have been set to seize them in focus — not the dimmer, distant stars. However there are some photos the place you’ll be able to see stars in area. Apollo astronauts left the digital camera’s shutter open longer throughout some photographic experiments. The outcomes present pinpoints of sunshine behind the intense, fuzzy blobs which might be the overexposed Moon or Earth.
Amy Shira Teitel
Spaceflight historian, Pasadena, California
This text was first printed in 2019 and has been up to date with new pictures.
