astropy/astropy — pull request #1939 by mhvk (2013-12-31 19:59:55+00:00)
Title: Correct UT in calculation of TDB; closes #1938

Ensure UT is properly taken from midnight in the calculation of TDB. Use a slightly different approach from #1938, in using `day_frac` to get the time since midnight:
```
ut = day_frac(njd1 - 0.5, njd2)[1]
```