DSS Plate Finder Help

This page describes how to use the DSS Plate Finder.

Use the DSS Plate Finder to construct a list of Digitized Sky Survey plates available for a specific region of the sky and to select which plates to retrieve images from. This utility will let you select plates based on the epoch, color, or location of image on the plate.

Detailed instructions may be found below, but here's how you can get started quickly using the Plate Finder. Enter either a coordinate pair (RA and Dec) or an object name to be resolved into coordinates. (If you enter an object name, you can resolve it into coordinates before looking for plates, or do it all in one step.) Then hit the Find plates button. The Plate Finder will then look up the position among all the digitized plates currently in our jukebox (if you entered a target name, it will resolve it into coordinates first) and present you with a list of the plates from which an image can be extracted at that position, along with some information about each plate: emulsion, filter, plate epoch, pixel resolution, etc. You may then select a plate and extract the image from it.

Help on Input Fields

Object Name

The name of the astronomical object you want coordinates for. This should be a fixed astronomical target; the name resolvers cannot resolve moving objects (planets, comets, artificial satellites, etc.) into their coordinates. The object name should be the name of a star, nebula, galaxy, etc.

If the Resolver (see below) is set to Region, then the target name should be the name of a DSS plate, as given in the REGION keyword in the FITS header.

Resolver

The name resolver you want to use, if you want to get an object's coordinates; or the name of a specific DSS plate.

To resolve an astronomical object's name into its coordinates (fixed targets only; planets, comets, asteroids, etc. are not listed in the name resolvers' catalogs), enter the object name in the Object Name field, select either NED or SIMBAD for the resolver, and hit the Get coordinates from button. The form will be redrawn with the object's right ascension and declination entered as defaults in the RA and Dec fields. Resolving an object name will not change any other choices made in the form.

Alternatively, you can just hit the Find plates button instead of Get Coordinates from, and the object name resolution and plate finding will all be done in one step.

If you select Region for the Name Resolver, then instead of an astronomical object, the Object Name will be interpreted as the name of a specific DSS plate, as it appears in the REGION keyword of a DSS FITS header. For example, an "object name" of XP443 will find the plate XP443. In this case, pressing Get coordinates will redraw the form with the plate's coordinates in place, while Find plates will go directly to the platemap for that plate. (Currently, plate IDs such as A1VA, are not yet recognized.)

RA,Dec

You can enter a Right Ascension and Declination in thses fields. 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 some electronic publications. However, this is not true for minutes: 31'.98 will be parsed as 31 minutes, 0.98 seconds.

Equinox

The equinox of the RA and Dec you have entered, either B1950 or J2000.

Height,Width

The height and width of the image. You can set this before or after getting a plate list.

Format

You can select either FITS or GIF for teh format of the data. If you select FITS, the images will be sent back to your browser with a MIME type of image/x-fits; if GIF, the MIME type will be image/gif.

Help on Output Fields

Survey Name: The name of the photographic survey to which the plate belongs.
Emulsion + Filter: The emulsion and filter used for the plate.
Region: The survey region name for the plate.
Epoch: The plate epoch (i.e., when the exposure was made).
Plate Scale: The scale of the digitization, in arcseconds per pixel.
Image Center on Plate: The location of the image center, in pixel numbers, with (1,1) at the southwest corner of the plate.
Image Center to Plate Center: The distance in arcminutes between the center of the extracted image and the center of the plate.
Image Center to Plate Edge: The distance in arcminutes between the center of the extracted image and the edge of the plate. The closer you are to the edge of a plate, the more distortion you're likely to see. If you're close enough to the plate edge, it will actually appear in your image as a sudden cutoff in the astronomical part of the image. When an image center is less than 15.0 arcminutes of a plate edge, the number reported here will be rendered in red.

Planned improvements and bug fixes

These are the bugs I know about. Since the Plate Finder is maintained on a time-available basis (which means I can't spend too much time working on it), I can't promise a schedule for fixes.

Big bug: Platemaps containing the 00h meridian don't show objects to the east of it.
Zoom in on a platemap.
Extract multiple images at once.
Plot catalogs on extracted images.
Efficiency improvments.
Several improvments to the code internals.
Add choices for catalogs in platemaps (colors, labels, etc).
Fix the labelling checkbox.
Fix PDF conversion to not crop.
Use selection region for archive searches.
Need a better name for it!