Half a lifetime

[cjsmith]

Presuming I was born around three in the morning (JD 2439769.83333), and the party with the backrub chain was roughly 10pm EST (JD 2447106.625), I will have been with Rob half my life at 2pm PST, December 8, 2007 (JD 2454443.41667).

Geek. Geek. Geek.

(I think I would have run in terror if somebody had told me during that backrub chain that when I was forty I'd be doing this math.)

Comments

[excessor.livejournal.com]

What does JD mean?

[fyellin.livejournal.com]

Julian Day.

To quote Wikipedia:

"The Julian day or Julian day number (JDN) is the integer number of days that have elapsed since the initial epoch defined as noon Universal Time (UT) Monday, January 1, 4713 BC in the proleptic Julian calendar. The Julian date (JD) is a continuous count of days and fractions elapsed since the same initial epoch. . . . The integral part (its floor) gives the Julian day number. The fractional part gives the time of day since noon UT as a decimal fraction of one day or fractional day, with 0.5 representing midnight UT."

Aren't you glad you asked?

[excessor.livejournal.com]

Yes, thank you. I did a google search of JD and just got a bunch of results regarding legal programs. So I went to a site that talks about units of time measurements, but didn't find anything there. Hence, my question.

It seems counterintuitive to have defined JDN to start at noon and not at midnight.

[fyellin.livejournal.com]

It was designed for European astronomers. This way, they wouldn't have to switch dates in the middle of the night.