| MadSci Network: Astronomy |
The answer to your original question, The location of the Tropic of Capricon, is related to the obliquity of the ecliptic.
The answer to your question about degrees is that we inherit the degree system from the Babylonians: 1 degree = 60 arcminutes = 3600 arcseconds. Thus, 0.5 degrees = 30 arcminutes, which is also written 30'. (1 arcminute = 1' and 1 arcsecond = 1".)
Thus, 0.5 degrees = 30'. However, 27' = 0.45 degrees, which if you round becomes 0.5 degrees.
If you asked me, I'd accept either 23.5 degrees or 23 deg. 27', but not 23 deg. 30'.
Try the links in the MadSci Library for more information on Astronomy.