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FAQs about Astronaut Photographs
- How many photographs have been taken?
Astronaut photography began with the first manned space flights in 1961. As of February 2000 the database contained over 380,000 images. A link to a detailed and up-to-date tally of the number of photographs by scale, cloud cover, and other aspects of interest to technical users is at:
http://earth.jsc.nasa.gov/sseop/sql.htm - North is not at the top of the photograph, is there some mistake?
Astronauts take these photographs out of the windows of spacecraft, and the camera can be in any direction relative to the Earth. Because of this, North can be in any direction relative to the top of the photo. This is the nature of the photography and is not an error. To better interpret photos, you can print them out and then rotate the paper until North matches the direction on a map. After getting some practice, you will be able to rotate the images mentally to match them to geographic references. - Why can't you see stars or galaxies in the photographs that show the curvature of the Earth and part of the black background of space?
The reason you can't see stars in high oblique photos is that the film speed is too slow and the shutter speed is too fast. Most of the films used are 100 ASA color positive. Fast shutter speeds are used to eliminate blur from the motion of the spacecraft. These films and shutter speeds would not be suitable for photographing stars from the Earth either. One exception to this rule is when astronauts use films and camera settings specifically to photograph features such as the Aurora Borealis and Aurora Australis. In these cases stars also show up in the photograph. The photos are also slightly blurry because very long exposures are needed to capture these dim nighttime features. - Is it true that the Great Wall of China is the only human-made object that can be seen from space?
No. In fact there are many, many human-made objects that can be seen from space without magnification – such as buildings, mines, irrigated croplands, salt evaporation ponds, jetties and landfills along coasts, and yes, roads. - Cities are easily visible, and at night, city lights. Of course, the further you get from the Earth, the fewer human-made objects you can see. Astronauts on the moon saw less detail when they looked at the Earth than astronauts on the Space Shuttle or Space Station see today. The most interesting part about the about the Great Wall of China is that astronauts cannot readily see it, even from low orbital altitudes. The wall is not that wide, and made from native materials that match the color of the surrounding landscape. It can be viewed using radar to create an image (the wall acts as a reflector), but cannot be seen on astronaut photos, even with a long lens.
- Where can I find a photograph of the whole Earth as seen from space?
Products are available that have actual clouds, and have the clouds removed at http://earthobservatory.nasa.gov/Newsroom/BlueMarble. - Where can I find pictures of the Earth at night showing city lights?
Although astronauts sometimes take pictures of the Earth at night, their pictures only show small regions. NASA and NOAA scientists have made a composite form satellite images that shows the Earth at night. See an Earth Observatory Article on City Lights for more information. Nighttime satellite images from the Defense Meteorological Satellite Program are compiled on a website maintained by the International Dark Sky Association at http://www.darksky.org. - How can I see pictures of Mount Everest?
There is an interactive tutorial that will help you see Mount Everest as the astronauts do at http://earth.jsc.nasa.gov/education/Everest. - What areas do the photographs cover?
Astronauts have photographed much of the world's surface. The area that an astronaut on a specific mission can see and photograph depends on the altitude and inclination of the spacecraft. It also depends on the daylight cycle on the ground when the spacecraft passes over an area. Space Shuttle missions usually vary in inclination from 28.5 to 51.6. The inclination gives a rough estimate of the maximum and minimum latitudes visible to the astronauts. For more information, see the EarthKam library under Satellite Ground Tracks at http://www.earthkam.ucsd.edu.
28.5 degree inclination sample coverage
Click for a larger image.
28.5 degree inclination sample coverage
Click for a larger image.
- What are the smallest objects that can be seen in the photographs?
As far as ground resolved distance is concerned, our best case so far (with a 250 mm lens) is resolving 8-meter objects on the ground. These have included building shadows, roads, and boats in harbors. Most photographs have much lower resolution. - Since astronauts are traveling so fast in orbit, why don't the photographs look smeared?
If you do the calculation for the amount of ground smear expected based on the shutter speed of the camera and the velocity of the Shuttle or space station relative to the ground, you would expect that the ground resolved distance could be no better than about 30 m. Because we have much better resolution (i.e. boats in harbors, narrow roads), we know that consciously or unconsciously, astronauts track the Earth when they take a photo, so the resolution is actually better than you would calculate. For more FAQ, visit http://earth.jsc.nasa.gov/faq.htm
