Work in progress. The Magellanic neutral hydrogen stream, if we could see it, as it would appear from Cardiff. Maybe. Not entirely certain (read : it might not be wrong) I've got the orientation right. Size of the stream in the sky is probably about right, although it's possible the whole thing needs to be shifted further south so less of it might be visible . On the other hand I didn't check the field of view of the image so it's possible the stream should appear even larger than is shown. Lots of checking still to do.
In any case, from some parts of the world the stream would most certainly appear far larger than this, so in terms of showing how much more dramatic the the sky would be in neutral hydrogen, it's not far wrong.
Oops. Turns out the stream wouldn't be visible from Cardiff at all... at least, not the part detected in this particular data set (http://www.astro.uni-bonn.de/en/download/data/lab-survey/). I seem to have rotated the view 90 degrees too far south - the tip of the stream would be just below the horizon. I don't know why I found that so difficult, all I needed to do was find Polaris, rotate the view down by the latitude of Cardiff (51 degrees) then correct for the camera FOV, to find the visible horizon. Oh well.
ReplyDeleteOther, more sensitive surveys have found that the stream extends about 40 degrees further than in this one, but at fainter levels. So something might be visible, but nothing like what's shown here. Unfortunately those data sets aren't publically available (at least not easily).
LAB data also turns out to be unsuitable for showing the more general sky at 21cm (as opposed to the Magellanic Stream specifically) : 0.6 degree resolution just isn't good enough when your FOV is only 40 degrees. Looks like I either have to find some much wider FOV images (Google street view, maybe) or use higher-resolution HI data (VLAGPS is a possibility).