Is there a service that will deliver a feed containing the union of tagged items for one tag across a set of various services? For example, the union of:

del.icio.us/tag/astronomy
technorati.com/posts/tag/astronomy
flickr.com/photos/tags/astronomy
connotea.org/tag/astronomy
wordpress.com/tag/astronomy/
…etc…

Easy to do, I suppose, but I don’t want to reinvent a wheel.