Frequently Asked Questions About Astronaut-Acquired Photographs

Questions about access to photographs:

What information is available about each photograph?
What kind of film is used?
What are "nadir," "near vertical," and "oblique" views?

What information is available about each photograph?

Every photograph taken of the Earth is examined and data about its location are entered in a database. These data include the approximate latitude and longitude of the center of the photo, geographical information about the political location, and a short text description of features included. A variety of other information about the images are also included such as degree of cloud cover, exposure, lens used, whether the image was nadir-viewing or oblique. For newer photographs, orbital information is included--the nadir position of the shuttle over the Earth and its altitude at the time the picture was taken. A detailed description of fields in the database is also available.

What kind of film is used?

In the past, photographs taken used primarily color positive film, however, black and white and color-infrared film were also used. Over the past few years, digital cameras have been used more extensively. This had the advantage that the images and be transmitted back to the ground and the images are already digital and ready for distribution on the web. Additional details about cameras and film are available in the database record for each image.

What are "nadir," "near vertical," and "oblique" views?

Unlike robotic satellites, which look Earthward with a fixed geometry, the human astronaut can look out the window of the spacecraft at any angle. If the astronaut looks toward the nadir of the orbit, he or she is looking directly down at the earth with no tilt angle. If the astronaut looks at some angle off the orbit track, he or she is looking at an oblique angle. Oblique photographs are classified as high oblique if the horizon or atmospheric limb can be seen. Photographs are classified as low oblique if they are intermediate between nadir and high oblique. In the database, the "tilt" field records NV (near vertical) for photos that have a center point within 1 degree latitude and longitude of the spacecraft nadir, HO (high oblique) for photos that include the horizon, and LO (low oblique) for the remaining photos.