Solar X-Ray Images From Skylab Available Over the Internet

Volume 11, Number 1, March 1995
By Dave Batchelor
The National Space Science Data Center (NSSDC) holds 1,451 digitized images from the Skylab S-054 X-ray telescope. Most of the images are 1,243 x 1,244-pixel arrays, produced by scanning the original photographic film with a microdensitometer; some are smaller in dimension, very few are larger. Using today's image display technology, these digital versions of the images are far easier to access, manipulate, and analyze than the original photographic products. The access is made particularly easy by an automated software system for retrieving images from the archive on optical disk and staging them to temporary disk space from which a requestor can copy them over the Internet, using ftp.

Of high historical and scientific importance, these images were obtained with the Apollo Telescope Mount aboard the Skylab space station from 1973-74. The images show the structure of the two-million-degree corona of the Sun, as well as transient phenomena such as solar flares. The S-054 X-ray telescope, built by American Science & Engineering (AS&E), revealed coronal structure invisible from the ground at unprecedented angular resolution (a few arc seconds), and the observing program accumulated a record of the evolution in the corona on timescales from seconds to 8 months. The synoptic record of solar coronal structure provided by these images has enabled researchers to discover trends in the lives of solar active regions, X-ray bright points, coronal streamers, and other solar wind structures, as well as the evolution of the solar magnetic field over an 8-month interval.

Originally, these images were acquired in orbit on photographic film, and processed by printing slides and paper images. (A popular movie was produced from selected images, showing the rotation of the glowing corona to dramatic effect.) Years later, the microdensitometer scans of the original film were made by AS&E researchers and stored there on magnetic tapes. NSSDC holds the tapes from AS&E and has migrated the data to new tape cartridges. The images are available for distribution to solar researchers through NSSDC's standard data request channels. Because of the importance of the images and the enhanced convenience in analyzing them quantitatively with modern computers and image display technology, NSSDC has placed the S-054 images in online access via the NSSDC Data Archive and Distribution System (NDADS).

Solar researchers are invited to make use of these data. Suggested uses are for studies of the Sun going back to the S-054 observing interval (May 14, 1973 to February 8, 1974), for comparisons with more recent rocket and spacecraft observations, for testing software to be used in current and future missions (e.g.,Yohkoh, SOHO), or for educational purposes. The images can now be used even by PC users with VGA graphics adapters, with software supplied by NSSDC.

To obtain an image for a specific date in the interval given above, one can send an E-mail message to the Internet address: with the Subject: request skylab image and the body of the message consisting only of a date in the format 730531. The system will search for all images on May 31, 1973, and stage them to the area open to anonymous ftp; in general there may be a large number of files or none.

The requestor should wait for a confirming E-mail message, which should contain references to finding one or more files with names like SKYLAB_730531_hhmmss.DAT. Upon receiving the message (which may take 15 minutes or more at busy times, or less off peak usage hours), the user should initiate an ftp session such as:

System_prompt> ftp
ndadsa> user anonymous
password: user's.Internet.address
ndadsa> cd [.data_dist]
ndadsa> cd skylab
ndadsa> dir

ndadsa> binary
ndadsa> get filename.DAT
ndadsa> bye
The data file format has not been altered from the original investigator team's 1973 specification, IBM 360 single-precision floating point code. Users may obtain C-language software to reformat the data to current computer binary data formats from NSSDC. Documentation of the salient contents of the data file headers, such as dates and times, is also available from NSSDC. (Other data of possible interest to solar physicists exist on NDADS. To obtain an up-to-date summary, send E-mail as above, except with a Subject: Holdings and no text body in the message. The system should reply with a brief list of current data holdings.)

Address any questions or other requests for data from NSSDC to:

          Coordinated Request & User Support Office
          NSSDC/Code 633
          NASA/Goddard Space Flight Center
          Greenbelt, MD 20771
          Telephone: (301) 286-6695
          FAX: (301) 286-1771
          Telex: 248496 or 197640
          TWX: 7108289716

David Batchelor
NSSDC Solar Specialist

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Author:Miranda Beall
Curators: Erin Gardner and Miranda Beall
Responsible Official: Dr. Joseph H. King, Code 633
Last Revised: 04 Dec 1996 [EDG]