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How to use the CGI script directly


Get an Object's Coordinates

To get an image from the Digitized Sky Survey, you will need the right ascension and declination of the area you're interested in. However, if all you know is the name of an object and don't have its coordinates handy, you can use this section to get the coordinates for you.

The coordinates will come from either the SIMBAD database in Strasbourg, France, or the NASA Extragalactic Database (NED) in Pasadena, California. SIMBAD contains comprehensive lists of all kinds of objects from all the major astronomical catalogs, while NED concentrates on objects outside our galaxy. (Neither can return coordinates for solar system objects.)

To get an object's coordinates, enter its name, select a resolver, and hit the "GET COORDINATES" button. The form will redraw itself with the object's coordinates filled in.

Getting an object's coordinates may take a moment if the networks are busy, so please be patient.


Retrieve an Image

This is the section where you specify what kind of image you want.

NOTE: Any entries you make in this section of the form will be erased if you use the "GET COORDINATES" feature!

Generation
Here, you select which generation of the Sky Survey you want. The First Generaton comprises the older surveys, scanned at about 1.7 arcsec per pixel. The Second Generation is from a newer ongoing survey, scanned at about 1 arcsec per pixel. Consequently, the images from the Second Generation scans will be larger than from the First: a 15'x15' Second Generation FITS image will be about 1.5 megabytes (a First Generation scan of the same size is about 570 kilobytes), so you may want to select smaller scan sizes when getting images from the Second Generation survey.

Coordinates (RA, Dec, and Equinox)
Enter the Right Ascension and Declination on which you would like the scan to be centered (you won't need to enter it if you use the Target Name Resolver), and select either J2000 or B1950 for the equinox of the coordinates.

A number of formats are accepted for the RA and Dec. Here are some examples:

    Decimal Degrees
        185.63325 29.8959861111111
 
    Hours, minutes and Seconds
        12 22 31.98      29 53 45.55
        12h22m31.98s     29d53m45.55s
        12:22:31.98     +29:53:45.55
        12h22'31.98"     29d53'45.55"
        12h 22m 31.98s   29d 53m 45.55s
        12h 22' 31.98"   29d 53' 45.55"
        12h 22' 31.98"  -29d 53' 45.55"
        12h22'31".98    -29d53'45".55
        12h22m31s.98    -29o53m45s.55
        12h 22' 31".98  -29d 53' 45".55
     
    Hours/Degrees and Minutes (no seconds)
        12 22     29 53
        12h22m   +29d53m
        12h22m    29d53m
        12:22m    29:53m
        12h22'    29d53'
        12h 22m   29d 53m
        12h 22'   29d 53'
        12h 22'  -29d 53'
 
    The RA may be given in decimal degrees by indicating
    a D or d after the degrees:
        12d 22m   29d 53m
Spacing is not important, as long as the value is unambiguous, and that you can delimit the hours/degrees, minutes, and (optional) seconds with letters, colons, spaces, or any character that's not a digit or a decimal point.

Note also that seconds of the form 31".98 or 31s.98 are accepted. This should make it easy to cut and paste values into these fields from electronic publications.

Image size
Specify a field size for the for the returned image by entering a height and width in arcminutes. The default size is 15' x 15', which yields a FITS file of about 530 kbytes, or a GIF image of usually around 160 kbytes. (The maximum size, 60 arcminutes, produces an 8-megabyte FITS file.)

Format
Select either FITS or GIF.

FITS files will be delivered with a MIME type of image/fits;
GIF files will be delivered with a MIME type of image/gif.

If you are using a graphical Web browser (Mosaic, Netscape, etc), you may be able to configure your browser to display the FITS images returned by this form instead of saving them to disk. Here is an example, showing how to configure a Unix-based browser for displaying the images in SAOimage.

Compression
Select a compression method. This will only be applied if you select FITS as the image format.
  • NONE - the FITS file will be delivered uncompressed.
  • Unix - The FITS file will be compressed with the Unix compress command.
  • gzip - The FITS file will be compressed with the gzip command.

Field of View Overlay
If you would like the HST field of view (FOV) overlaid onto a GIF image from the First Generation scans, you can select that here. The FOV shows the placement within the field of the apertures of HST's science instruments for a given spacecraft roll angle. Select:
  • NONE - No FOV will be drawn on the image.
  • LAUNCH - After launch of HST in Apr 1990 and before the First Servicing Mission in Dec 1993 (the pre-COSTAR era).
  • SM93 - After the First Servicing Mission, Dec 1993, and before the Second Servicing Mission, Feb 1997 (post-COSTAR, but before STIS and NICMOS).
  • SM97 - After the Second Servicing Mission, Feb 1997, showing STIS and NICMOS apertures.
and enter the desired Roll Angle. (This is the V3 roll angle, 180 degrees from the U3 roll angle.)

HST's total field of view is about 30 arcminutes across, so to get the entire FOV in the image, you will need to select a height and width of about 30' x 30'. (A 25'x25' field will also show the FOV will a little clipping at the edges.)

Remember, FOVs may only be drawn on GIF-formatted images from the First Generation Survey. If you select FITS, or if you select another survey, then your FOV selection will be ignored.