How Cameras In Space Miss The Stars

It is possible to see stars in space, but they rarely show up in photographs taken by astronauts in orbit or on the Moon. This is because stars are very far away and appear dim in contrast to other objects in the foreground of the photographs. The camera's exposure settings, which determine how light or dark an image is, are usually set to capture the bright foreground objects, meaning the faint light from the distant stars isn't captured. The human eye can see stars in space because it adjusts its sensitivity to light, but cameras don't have the same flexibility.

Camera settings for daylight conditions

When taking photos in daylight, the sun is at its highest intensity and brightness, and light bounces and reflects off every possible surface. This creates harsh glare and sharp shadows, which can be a challenge for photographers. To capture the best images in these conditions, you need to adjust your camera settings to suit the conditions.

There are three main variables that can be changed on a manually operated camera: shutter speed, aperture, and ISO.

Shutter speed refers to the length of time the camera sensor is exposed to light. For example, a shutter speed of three seconds will allow you to capture a firework in the night sky, while a speed of 1/1000 of a second will capture a sharp action shot.

Aperture refers to the diameter to which the shutter opens. A larger diameter, measured in F-stops, lets in more light but results in a shallower depth of field. For landscape photography, an F-stop between 2 and 5 is recommended to keep the foreground in focus. For a sharper image with a larger area in focus, you would need to increase the F-stop to between 9 and 12.

ISO controls the sensitivity of the camera sensor. Increasing the ISO value will brighten the image and is useful in low-light conditions. However, a very high ISO can cause the image to become grainy and soft.

To capture the best images in bright daylight, photographers need to balance these three variables to produce the desired image. For example, when shooting action sports, a fast shutter speed and high F-stop will help freeze the motion and keep the action in focus. However, this may require increasing the ISO, which can result in grainier images.

One rule of thumb for shooting in bright sunlight is the "Sunny 16" rule. This rule suggests setting the aperture to f/16 in full sun, keeping the ISO around 100, and setting the shutter speed to about 1/100 or 1/125. However, you may need to adjust these settings based on your camera and specific lighting conditions.

Additionally, photographers can use techniques such as shooting in the shade, using fill flash, or creating their own shade with umbrellas or reflectors to improve lighting conditions when shooting in bright daylight.

Cameras have a limited range of ability to see light and dark

The shutter speed for capturing stars at night needs to be much longer than that for shooting objects and landscapes during the day. Therefore, a camera on board a space station flying over the illuminated side of the Earth has little chance of seeing the stars. The longer the exposure, the more light falls on the lens, which helps to capture relatively dimmer sources of light. However, a long exposure setting will also capture the bright object in the foreground, resulting in it being overexposed and washed out.

The human eye adjusts to a certain level of illumination. During the day, sunlight is too intense for the eye to observe such weak sources of radiation as distant stars. The same is true for cameras in space; the level of illumination in the presence of the Sun or the sunlit part of the Earth is too high, and the camera cannot capture the stars in the black sky.

The brightness of an object is directly related to the number of photons that reach a recording device such as a camera. The shutter must be open for a longer period to capture an image of a dim object. For example, a decent photo of the full moon requires a shutter speed of about one or two seconds. In contrast, capturing the image of a star necessitates a shutter speed ranging from several minutes to several hours to collect enough photons to create an image.

The brightness of the moon

The Moon's brightness can be measured by its albedo, which is the amount of light it reflects. The Moon's average albedo is 0.11, meaning it reflects about 11% of the Sun's light. In comparison, the Earth has an average albedo of 0.37, reflecting approximately 37% of sunlight. This is because the Earth's surface includes highly reflective materials like snow, ice, clouds, and deserts. Interestingly, deep water has a relatively low albedo, ranging from 0.07 to 0.10, so if Earth were covered only in oceans, it would be slightly less reflective than the Moon.

The dynamic range and exposure settings of cameras also contribute to the challenge of capturing stars in space photographs. Cameras have a limited ability to capture the contrast between bright objects like the Moon and the dimmer stars. With short exposure times, the bright object is clearly captured, but the stars are too faint to be visible. On the other hand, with long exposure times, the bright object becomes overexposed, and the stars may still not be bright enough to be seen.

To capture the stars in a photograph with a bright object in the foreground, one would need to use a very long exposure time, which is not typically feasible for space cameras. Additionally, the bright object would likely cause lens flare or other artefacts that would further obscure the stars. Thus, the brightness of the Moon and other celestial bodies, combined with the limitations of camera technology, make it challenging to capture stars in space photographs.

The brightness of the Earth

The human eye is much more sensitive to light than a camera. When taking a photo with a camera that is backlit, the photographer can see the features and colours of the object, but when the picture is developed, only the shadow outline can be seen. The same is true for astronauts taking pictures of the Earth. The sunlight reflecting off the Earth is so bright that the shutter speed of the camera has to be a fraction of a second. If the exposure was longer, the camera would absorb too many photons, and the Earth would appear washed out.

The brightness of an object is directly related to the number of photons that reach a recording device, such as a camera. To get a decent photo of the full moon, the shutter should be open for about a second or two. To record the image of a star, the shutter must be open for several minutes to several hours.

Cameras have a limited range of ability to see the contrast of light and dark. When focused on something reflecting a high amount of light in a dark field, it is very hard to see much lower levels of light. If the camera was set to see the stars, the nearby object would wash out the whole picture.

Therefore, the brightness of the Earth, when lit by the Sun, is the main reason why stars cannot be seen in photographs taken by cameras in space.

Cameras can't adjust their aperture

The aperture of a camera is the opening that lets in light, and it can be adjusted to control how much light enters the camera. In space, the camera's aperture needs to be set to let in enough light to capture the intended target, such as a planet or an asteroid. However, the stars in the background are too dim and far away to be captured by the camera with the same aperture setting.

Most space cameras have a fixed aperture and cannot adjust it like fancy cameras or human eyes, which dilate and contract their pupils to control the amount of light entering. This means that the aperture of a space camera is designed based on the predicted light levels the camera will encounter during its mission. As a result, the camera may not be able to capture both the bright foreground objects and the faint stars in the same image.

For example, the OSIRIS-REx spacecraft's MapCam was designed to study the colours of a very dark-toned asteroid. However, when it tried to capture an image of the Earth, it was overwhelmed by the brilliant light reflecting off the bright clouds, causing artefacts in the image. In this case, the camera's aperture was not able to adjust to the different lighting conditions, and the stars would be even more challenging to capture due to their distance and dimness.

To capture the stars in a space image, a longer exposure setting is required. A longer exposure allows the camera to collect light for a longer duration, helping to detect fainter objects. However, with a short exposure setting, which is typically used for bright foreground objects, the stars will not be visible as they will be underexposed.

Therefore, the inability of cameras to adjust their aperture based on the lighting conditions in space is one of the main reasons why stars are not visible in many space images. The camera needs to be configured with the appropriate settings to capture the intended target, and the stars often do not have enough light to be detected with those settings.

Frequently asked questions