name::finding plates by time and place
query:: 
SELECT accref, exposure FROM lsw.plates
	WHERE
	 dateObs BETWEEN 'J2416128.5' AND 'J2416133.5' AND
	 1=CONTAINS(REGION('simbad Aldebaran'),
		 CIRCLE('ICRS', centerAlpha, centerDelta, 15))
description::
(This contains some tutorial-style material)

Suppose you read in an old amateur observer's log there was an unexpected
object on the night sky in the cold winter nights of the week between January
12th and 18th, 1903.  The plate scans from Heidelberg in :taptable:`lsw.plates`
are an ideal material for searching for photographic records (as is
:taptable:`ivoa.obscore`, but that was added when this example had already been
written)::

  SELECT centerAlpha, centerDelta, dateObs FROM lsw.plates 
    WHERE dateObs BETWEEN '1903-01-12' AND '1903-01-19'


As you can see, dates are entered in quotes, just like any string.  The
engine understand more than just the ISO format (yyyy-mm-dd).  See the
chapter on standards compliance in 
`our ADQL documentation </__system__/adql/query/info>`_ for details.  
Also note that we wanted the 18th to be included and therefore passed
1903-01-19 as the upper limit.  Dates without times always count as 00:00 hours
of the day, so anything with a time *on* this day is not included.

Say you start looking for hints as to where the object might have been.
Eventually, you figure out it was "near the Aldebaran".  You could use
Simbad to get its position and then query like this::

  SELECT accref, exposure, tmEnd FROM lsw.plates
    WHERE 
      dateObs BETWEEN 'J2416128.5' AND 'J2416133.5' AND
      1=CONTAINS(POINT('ICRS', centerAlpha, centerDelta),
        CIRCLE('ICRS', 69, 16, 15))

to see if any plate center is 15 degrees around Aldebaran's (rough ICRS) 
position.  And indeed, we have two of them.  

There is also a shortcut via regions.  A ``REGION`` stands for
some kind of "geometry", i.e., point at or part of the sky, and site
operators are free to define what the arguments mean.  At the GAVO DC,
one way of specifying a region is via Simbad, like this::

	SELECT accref, exposure FROM lsw.plates
		WHERE
		 dateObs BETWEEN 'J2416128.5' AND 'J2416133.5' AND
		 1=CONTAINS(REGION('simbad Aldebaran'),
			 CIRCLE('ICRS', centerAlpha, centerDelta, 15))


Note how we needed to switch around the roles of Aldebaran's position
and the positions we got from the database.  There currently is no
way to say "get a circle around a Simbad position".  If you need
this at some point, let us know.  Also note that you cannot pull
a name from the database and try to resolve it via Simbad.  For many
reasons we would be very reluctant to add such a functionality.
..