Astrotagging for developers
We really want you developers out there to get your hands on astrotags and see what it's possible to do with them.
Astrotagging is the celestial equivalent of geotagging. Where geotagging uses the geo: namespace, astrotagging uses machine tags in the astro: namespace. Thanks to Astrometry.net our astronomy photos have machine tags identifying celestial position, field of view and objects in each photo. Now, what can we do with these tags?
Celestial mapping with astro:RA and astro:Dec
astro:RA and astro:Dec contain the right ascension and declination of the centre of the photo. Like latitude and longitude for geocoded photos, right ascension and declination give us the position of a photo as a point on the celestial sphere. We can then map our photos and group them by proximity to each other, just as we already do with geocoded photos of places on the Earth.
The celestial sphere is divided into 88 constellations, defined by the International Astronomical Union. Each point on the sky belongs to a single constellation. We can use astro:RA and astro:Dec to associate each photo with a constellation, opening up the possibility of something like Flickr Places on the sky.
Celestial mapping with astro:fieldSize and astro:orientation
astro:fieldSize tells us the angular extent of a photo on the sky. Similarly, astro:pixelScale gives us the angular size of a single pixel in the original, full-size image. astro:orientation tells us the orientation of a photo with respect to celestial north. Knowing the position, extent and orientation of a picture, we can overlay it on a map of the sky. The Astrometry.net robot, which tags our group pictures, already uses this information to link photos to Microsoft's Worldwide Telescope (Windows only, I'm afraid). Google's Sky Data in KML is a handy tutorial on how to use RA, dec and field of view (α) in Google Sky. One possible application of this information might be to overlay and mosaic photos of the same region of the sky. Another application would be to zoom in and out of a region by comparing photos at the same location but with higher and lower fields of view.
Name-based searching with astro:name
astro:name tags a photo with the names or catalogue designations of objects in the field of view. So we could find all photos of the Orion Nebula (NGC1976), for example, by searching for the tag astro:name=NGC1976. Since the names follow systematic, regular patterns it ought to be possible to go further and find all photos of objects in the New General Catalogue (astro:name=NGC*) or all photos of stars (astro:name=thestar*).
Hopefully these ideas have started you thinking about how to use machine tags in your own applications. Please join the discussion on our Flickr group and contribute your own ideas.