20160326

Times on this site

Someone asked what decimal time format I prefer, so I figure it's time I explain again the ones used on this site.
My default decimal time format is Modified Julian Dates. This combines the date and time into one number, is correlated to Universal Time (GMT), is shorter than Julian dates, and is in actual use by astronomers. Plus, they look like stardates. I put these at the bottom of every post, and also following any calendar dates, such as March 26 (57473). If I talk about other formats, I'll usually post the time and date in that one, too.

At the top of every page is the decimal time in French format, 10 hours/day, 100 minutes/hour, 100 seconds/minute, in your browser's local time.

In the sidebar I list several other formats:

Calendrier Républicain: the current date according to the French Republican Calendar used during the French Revolution, with French decimal time as it would have been written then, correlated to temps moyen de Paris (Paris mean time) which is 9.35 minutes (6.49 decimal minutes) ahead of GMT. The dates are calculated as they were during the Revolution, i.e. each year beginning on the day of the autumnal equinox, which may differ a day from other methods.

Excel: This is the Excel for PC serial date, which is a count of days from the beginning of 1900, including a decimal fraction which represents the time of day, in the computer's local time. This is what you get if you convert a date/time cell to numeric format in Excel.

TLE Epoch: this is the date/time used in Two-Line Elements, which are a compact way of describing the orbits of artificial satellites. The first two digits are the last two digits of the year between 1950 and 2050; the next three digits are the ordinal day of year, i.e. the number of days since the beginning of the year, and the decimal fraction represents the time of day in UTC to eight digits.

Julian Date: a count of days from the beginning of 4713 BCE, the decimal fraction representing the time of day correlated to noon GMT. This has been used by astronomers since the 19th century.

Mars Sol Date: the Martian version of a Julian date, being a count of Martian days, called sols, which are slightly longer than earth days, from the birth of the astronomer Carl Otto Lampland.

Swatch: Internet Time, created by the watch company, being a count of ".beats" (millidays) from midnight, Central European (Winter) Time.

STO Stardate: stardate format used in Star Trek Online, a massively multiplayer online role-playing game (MMORPG). They extend the stardates used on Star Trek: The Next Generation to 400 years from the present, incrementing by 1000 stardate units per year.

0h 59m 37s
Sextidi 6 Germinal an CCXXIV à 3 heures 57 minutes décimales t.m.P.
Excel 42455.05937
TLE 16086.35104660
JD 2457473.85104
MSD 50561.84066
@392.beats
SD 93838.67
MJD 57473.351

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