title: Converting from TAI modified Julian Day to Datetime
body: <p>I'm trying to convert from TAI modified Julian Day to datetime (and vice versa). </p>
  
  <p>I've been going through astropy's <code>Time()</code> documentation and I've gotten close:</p>
  
  <pre><code>from astropy.time import Time
  
  constantOffset = 2430000
  input1 = 27754.500428240735  # corresponds to 2017-01-01 00:00:00 in TAIMJD
  input2 = 27253.500416666669  # corresponds to 2015-08-19 00:00:00 in TAIMJD
  
  t1 = Time(input1 + constantOffset, format='jd')
  print(t1.datetime)  # 2017-01-01 00:00:37
  t2 = Time(input2 + constantOffset, format='jd')
  print(t2.datetime)  # 2015-08-19 00:00:36
  </code></pre>
  
  <p>What's going wrong here is that there is a changing offset based on the year - see <a href="http://maia.usno.navy.mil/ser7/tai-utc.dat" rel="nofollow noreferrer">http://maia.usno.navy.mil/ser7/tai-utc.dat</a></p>
  
  <p>I've played around with adding the parameter <code>scale='tai'</code> into the declarations for <code>Time</code> objects but that doesn't seem to change anything. </p>
  
  <p>Does anybody see a way to account for the unsteady offset?</p>
  
  <p>Could be helpful - <a href="http://docs.astropy.org/en/stable/time/" rel="nofollow noreferrer">http://docs.astropy.org/en/stable/time/</a></p>