'Modifed Julian Date' / 'Julian Date' question...

[RT65CB-SWL]

When does or when might an astronomer use the 'Modifed Julian Date' instead of  'Julian Date' ?

tnx in adv.

[AndrewRrrrrr]

we use MJD at work - the integer part of the MJD is a much smaller number than the JD and the "day" starts at midnight. The JD "day" starts at noon. 

The JD is probably more useful to an astronomer because the integer number does not roll-over at midnight, in the middle of a viewing session.

So it depends what you're doing really. Maybe something to do with being at sea in the old days - the only time you could determine exactly was midday when the sun is at its highest point in the sky. 

Just a few guesses really!!!!

[Xilman]

6 minutes ago, AndrewRrrrrr said:

we use MJD at work - the integer part of the MJD is a much smaller number than the JD and the "day" starts at midnight. The JD "day" starts at noon. 

The JD is probably more useful to an astronomer because the integer number does not roll-over at midnight, in the middle of a viewing session.

So it depends what you're doing really. Maybe something to do with being at sea in the old days - the only time you could determine exactly was midday when the sun is at its highest point in the sky. 

Just a few guesses really!!!!

In these days when 64-bit cpus are widespread the extra size of the full JD (of which there are many variants BTW) is not such a big deal as when 32-bit floating point was commonplace. There is a big difference between 6-7 digits precision and 15-16 bit precision!

Your "more useful" comment belies your location. 😉  Someone in Oz or NZ may politely disagree.