This view of Earth rising over the Moon’s horizon was taken from the Apollo 11 spacecraft. Credit score: NASA.
Why do photos 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 digicam settings used to take most images from the Moon weren’t designed to seize stars.
Apollo astronauts used movie cameras, so to grasp the reply, we have to clarify slightly bit about how digicam publicity works. Movie is a light-sensitive emulsion over plastic. When that plastic is uncovered to mild by way of the digicam’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 pace, each of which management how a lot mild hits the movie. A smaller aperture means much less mild, as does a sooner shutter pace. It’s nearly like how your pupil constricts on a brilliant day and dilates at night time: Your eye robotically adjusts your aperture in an effort to see in several situations.
A photographer additionally has to contemplate an important a part of the {photograph} earlier than setting aperture and shutter pace. 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 shall be dominated by a washed-out, overexposed focus.
Associated: Do you may have a space-related query? Ask Astro here.
Let’s say you’re Neil Armstrong photographing Buzz Aldrin throughout a brilliant 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 wish to select a quick shutter pace and a smaller aperture. The result’s a transparent picture of Buzz, however different mild sources, like the celebrities, are too dim to go away 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 pictures the place you may see stars in space. Apollo astronauts left the digicam’s shutter open longer throughout some photographic experiments. The outcomes present pinpoints of sunshine behind the brilliant, 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 images.
