Earlier I described my idea for an RSS-like XML feed for telescopes. The idea was to allow anyone to keep up with what particular telescopes were doing. In this post I will try to describe my current idea. First off, before I give a more detailed description of each part, let me show an example of what the finished thing may look like:
<?xml version="1.0" encoding="UTF-8"?>
<desc>The 42ft telescope at Jodrell Bank Observatory</desc>
<link href="http://www.jb.man.ac.uk/42ft.html" />
<image href="http://www.jb.man.ac.uk/vlbi/inter/42ft_72.gif" />
<object type="pulsar" name="Stuart's fake pulsar" />
<ra h="0" m="34" s="56.89" />
<dec d="+50" m="12" s="3.7" />
<az act="170.06" dem="169.5" />
<el act="70.06" dem="70.23" />
OK, now for a bit of a description. The first line is a standard start to an XML file. The second line defines the start of a telescope tag. I've defined a namespace at a currently non-existent URL but as far as I can tell, that doesn't actually matter. The remaining lines define aspects of the telescope. First of all we need to define a telescope in a way that would give remote applications a bit of useful background information:
- name - the given name of the telescope
- desc - a short description of the telescope for use in information balloons, short biographies etc.
- link - a relevant web link. I chose this over <a href=""> because having link text didn't seem to make sense
- image - this should be a picture of the telescope. Perhaps <img src=""> makes more sense but I was keeping away from HTML tags.
- Point - this follows the Geography Markup Language (GML) format for marking positions after a suggestion from Dave P. The coordinates are the latitude and longitude (in that order) of the telescope on the Earth and are given in degrees. This should probably be optional as it makes no sense for telescopes in space!
- height - the height above mean sea level in metres. Probably should be optional to space-based 'scopes.
This information would not be expected to change often. Next we define the time that this file was generated:
- time - the time that this file was generated in ISO 8601 date format. Dave P suggested this rather than the time format used in RSS files.
- status - a flag to specify things like "slewing", "observing" and"parked/closed/stopped". Should these words be defined?
- object - the aim here is to provide both a public-friendly description (the name attribute) and a computer readable flag (the type attribute) for the type of object. My suggested types are: asteroid, comet, dwarf planet, planet, star, nebula, ISM, galaxy, galaxy cluster, calibration object. However, the full A&A keywords list of objects may be better to work from as it is accepted within the astronomical community.
- position - this is where we finally get around to defining the position that the telescope is observing. The most important coordinates to report are the ra (Right Ascension) and dec (declination). I thought it would be sensible to give these broken into hours/degrees, (arc)minutes and (arc)seconds for maximum flexibility. It would also be possible for a telescope to omit the (arc)minutes/(arc)seconds attributes if they wanted to degrade the reported resolution for some reason. A given ra/dec only make sense if an epoch is also defined. I expect this will normally be J2000 but sometimes telescope systems still work in B1950. I also thought it would be good to have an azimuth (az) and elevation (el) specified in degrees, although these could be optional.