This FAQ is not intended to answer general questions about
NASA photos or information about solar system bodies.
These FAQs (for the sci.space newsgroups on usenet) are available at
The Internet FAQ Archive.
All of the images presented on NSSDCA's Photo Gallery are in the public domain. As such, they may be used for any purpose. NSSDCA does ask, however, that you acknowledge NASA and the NSSDCA as the supplier of the data. In addition, where the source of the image (by project or as a specific person) is credited in the text, you should also acknowledge that, too.
In addition, NASA further requires that NASA images cannot be used to imply endorsement by NASA.
The NSSDCA no longer supports requests for hardcopy prints of the images represented here or elsewhere on its web site. It is possible in some circumstances to request a higher resolution digital version that is available in the NSSDCA Photo Gallery. To obtain a hardcopy print, transparency, or slide of the images, however, you will have to contact a commercial firm in your area as to cost and acceptable format. To see if a higher resolution version of the image you wish is available from NSSDCA, please contact our Coordinated Request and User Support Office (CRUSO). You should have the photo number of the image(s) you want and the name of the mission for each photo.
The choice of JPEG format over GIF for the larger images was made for two different reasons. The first is a matter of size. In most cases, the JPEG images are smaller. In order to reduce the load on both our server machine as well as on the network and user's machine, it was felt that using JPEG compression was a reasonable alternative. It preserves most of the original image, but minimizes the file sizes.
The second consideration was one of color depth. Although most imagers on spacecraft in use today still have only a depth of 256 levels (gray scale), the color images which are on the photo gallery are often combinations of three such filters. Thus, even though the original single-filter images are only 8-bit (and therefore appropriate for the lossless GIF compression), the resultant color images are actually 24-bit. Since GIF compression gets rid of this additional color information, but JPEG does not, it was felt that the loss of color depth was much more severe than the loss due to using the JPEG compression.
Alas, no longer! Due to decreasing access and the ability of most browsers to handle large file downloads, we have decommisioned our FTP server and moved all of our services to our standard web server.
There are a number of reasons you might not have found what you're looking for in the NSSDCA Photo Gallery. First, the image(s) may not yet be available. Second, the image(s) may be available, but not (at least yet) from NSSDCA. Third, it may be something which no one has suggested be put up. Lastly, it may be outside the province of NSSDCA's responsibilities. In all cases, feel free to send your feedback and we'll try and address your concerns. However, you might also try first looking through the other sites to which the Photo Gallery provides links. The list is not a comprehensive listing of all sources of images, but covers most of the areas we are asked about most frequently.
Contact the EROS Data Center.
There are no missing data. This is a feature of the design of the particular instrument. The Wide-Field Planetary Camera 2 on HST has four CCD (charge-coupled device) detectors by which it creates an image. The four CCDs are arranged in a rectangular fashion, nominally forming a larger square. However, one of the CCDs has the same number of pixels as the other CCDs, but is only half of the dimension. Therefore the CCDs pictorially are arranged like this:
_____ | |__ |___|_|__ | | | |___|___|
The CCD ws primarily designed for high-resolution photographs of solar system objects (thus the planetary camera part of the instrument name), but on wide-field objects (such as nebulae) all four CCDs were used, thus giving the images their characteristic "bite-out" shape. The data are not missing (except in the sense that there is no detector in that position to image the data), it just is not captured because of the design.
Actually, for many of the images on the photo gallery, there are higher-resolution versions (in TIFF) available. When available, there is a link to these images in the column denoted "Hi-res TIFF?".