Previous page  Page 56   Next page    Table of Contents 

   University of Leicester, UK)

   You can visit these sites and get a DSS image in FITS format.  (GIF
and other formats won't work.)  Click on the "Add DSS Image" option,
and specify the name of the image you have just downloaded.  It will
be shown just as if you extracted the data from the CD;  only the
method of importing the image is different.
                                              
   To get DSS images from the Internet,  you should first center the
chart on the area of interest,  and zoom in or out to cover the desired
area.  DSS images from the Internet are limited to a maximum dimension
of 15 arcminutes;  ask for a larger dimension,  and it will get chopped
down to that size.

   Click on "DSS from Internet",  and there will be a slight pause while
the downloading function starts up.  After a second or so,  the hourglass
cursor will turn back to an arrow,  and the actual downloading of the
image will take place in the background.  This is a good thing,  since
the images can take a while to download.  The images are requested and
retrieved from an STScI (Space Telescope Science Institute) server,  and
the large size of the image files combined with the slow response of the
server can combine to cause it to take a few minutes to actually fetch
the image.  Because it is processed in the background,  you can continue
to do other things in Guide while this is going on.

   Once it's done,  though,  the chart will refresh and the image will
appear.
                                      
   If you have a dial-up connection,  as most of us do,  you should find
that if you aren't connected at the time you click on "DSS from Internet",
the standard Windows connection dialog should appear and dial in to your
ISP.  In some cases,  this fails to happen.  If so,  you will have to make
sure that you're connected to the Internet before selecting this function.

   By default,  the download will be from the DSS-1,  the "original"
DSS based mostly on photographs made in the 1950s.  More recently,
STScI has been creating the DSS-2,  from more recent data.  Both 'R'
(red-sensitive) and 'B' (blue-sensitive) plates have been scanned in,
and you can select the sort you prefer (or stick with the original
DSS-1).  DSS-2 was scanned at slightly higher resolution;  be warned
that this means larger downloads. Also,  DSS-2 is not available for
the entire sky;  in particular,  asking for DSS-2 B will frequently
result in an "image not found" message.

17b: USNO A1.0 AND A2.0           

   The USNO A catalogs each contain about 500 million objects.  The
first version,  A1.0, consumed ten CD-ROMs;  the second,  A2.0,
consumes eleven CD-ROMs and is the current record-holder for most
detailed dataset.  (A2.0 is an update to A1.0;  the positions and
magnitudes were recalibrated,  and different sources were used for

 Previous page  Page 56   Next page    Table of Contents