Do you ever closely observe space photos taken from telescopes or astronauts in space?
You will see one common thing in those images, there will be a brighter object like Moon or Earth and a black background. Those images do not have stars as we see in our night sky.
What is going on here!
As we know there are lots of stars in space, and if those images are truly captured in space then there should be stars, right?
No, it’s not possible.
In order to understand that, first you have to understand how a digital camera actually works. Generally, in a digital camera light comes from a lens and is exposed to a digital sensor, which subsequently, helps in forming an image that later gets saved into a memory card.
In olden days, in place of this digital sensor a film was used, but in either case, film or sensor image-making involves exposure to light. Exposure plays an important role when we take photographs.
What is Exposure and why its important for space photos?
If you ever used a camera, then maybe heard the term exposure before. Exposure is used to refer to the amount of light camera sensor captures while taking a picture.
Digital cameras are highly sensitive to light. If enough light cannot reach the sensor, then the image cannot be formed and as a result, a dark image will be captured. On the other hand, if more than enough light reaches then the sensor, then the image will be white-out/washed-out. That’s why it’s really important to precisely control the exposure of a camera.
The exposure of a camera is controlled by three key components of a camera – aperture, shutter speed, and ISO.
- Aperture – determines how much light is allowed through a lens.
- Shutter Speed – Determines the duration of light that is allowed through a lens.
- ISO – Determines the sensitivity sensor to light.
The connection between Exposure and stars in space photographs
As far as we know, perfect exposure settings help the photographer to capture an image perfectly. A photographer has to decide the primary object of the picture and adjust exposure settings according to that.
If you have a camera and want to capture a bright object then you need to keep the exposure of your camera low. This will allow a very little amount of light to expose the camera sensor as the object is already bright, this light is more than sufficient to get an image.
The same rule applied when you try to take a photo of an object in the space. To capture a photograph of a bright object like Earth, Moon, or any other large celestial body in space, you must keep your camera exposure short. By using short exposure settings you can capture sharp high-quality foreground images. However, if there’d been some dim objects in the background, you would not able to capture them.
This is exactly what happens when you try to take a photo in space. As Moon, Earth, or any celestial are too bright and in comparison to them the stars far away are too dim, so when you try to capture a photo in space, you would not able to capture the stars in the background.
Now, what if you use long exposure settings?
In this case, your camera shutter will be open for a long time and more light will able to pass through the lens. By using long exposure settings you will be able to capture stars but if there were any bright objects in the foreground then those will be overexposed. If the foreground object is too bright then it can wash out the whole image.
You can see in this GIF how sunlight overexposed the whole image when used the long exposure settings.
Effect on history – Why Aren’t There Stars in Apollo 11 the Moon Landing Photos?
We all know on July 20, 1969, Apollo 11 astronauts Neil Armstrong and Buzz Aldrin laid the first footprints on the moon. Due to the photographic challenges explained earlier, when they captured photographs that did not contain any stars, a vocal minority believed the mission to be a hoax and something filmed in a studio as those photos did not have stars in the background.
Later, Will Stefanov, one of the members of the ISS Crew Earth Observations Team explained this as: It’s dependent on the camera settings and to some degree the camera itself. The camera’s astronauts often use are Nikon D3 cameras which are designed to be more sensitive in low-light situations, so you are more likely to capture some bright stars in the imagery.
If an image has been taken with long exposures or wide apertures then those images will record more starlight due to the greater amount of light on the camera sensor. Cameras that use shorter exposure are unable to capture stars in the daytime. Those cameras are unable to capture stars as they are too dim compared to the brightness of the planet.
For Crew Earth Observation images, astronauts have to follow a set procedure which is defined by NASA. Those procedures also have defined camera settings. But occasionally, they will change those settings for a specific purpose or for personal experimentation.
So, now maybe you are thinking that it’s not really possible to capture a crisp image of the moon with stars. Then what about those images which we have seen Earth or Moon with stars?
Those are actually doctored or photo-shopped images, where images are edited to enhance their aesthetic value.