Wikipedia:Reference desk/Archives/Science/2024 July 16

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July 16

Next Julian period

Moved to here from the Mathematics section of the Reference desk —  --Lambiam 13:23, 16 July 2024 (UTC).

Julian day says that the next Julian period will begin in AD 3268. When representing dates after this period begins, do mathematicians/astronomers/etc. reset the date count to 1 in 3268, or do they continue incrementing dates unchanged from 3267? If this is answered in the article, I missed it. Nyttend (talk) 21:57, 15 July 2024 (UTC)

I'm not convinced this is a math question, so perhaps it should be migrated to the science or computing desk. Are there people who actually need to keep track of dates that far in the future? --RDBury (talk) 02:14, 16 July 2024 (UTC)

I would suggest asking the question again some time after the year, say, 3250, when the people in charge have started thinking about it. Personally, I would think that resetting would be rather inconvenient and serve no practical purpose. --Wrongfilter (talk) 12:21, 16 July 2024 (UTC)

nasa.gov already has free Julian astrometry to day ~5,373,483 (Anno Domini 9999, if they ever go to 9,999,999.999999999 you could get major solar system object positions till December 20th 22666 AD (a Thursday)). Sagittarian Milky Way (talk) 18:10, 16 July 2024 (UTC)

Wikipedia lists many observable astronomical events that will occur in the next Julian period, so presumably some astronomers are already thinking about it and may even have developed a convention. I don't know, though, whether they are "the people in charge".  --Lambiam 13:19, 16 July 2024 (UTC)

The people in charge would be one of the IAU commissions. --Wrongfilter (talk) 13:46, 16 July 2024 (UTC)

No resetting: the Julian date is a continuous count. The epoch is fixed to the beginning of the current Julian period, it doesn't float to the beginning of the Julian period of times in the distant future. See for example "The Julian and Modified Julian Dates" by Dennis McCarthy from the USNO: "The Julian day number (JD) is the number assigned to a day in a continuous count of days beginning with the Julian day number 0 assigned to the day starting at Greenwich mean noon on 1 January 4713 B.C., in the Julian calendar extrapolated backwards ('proleptic')." Similarly, if you look into the IAU's SOFA software, it uses a fixed epoch, and defines the range of valid dates for the conversion routines [1], [2]: "The earliest valid date is -68569.5 (-4900 March 1). The largest value accepted is 10^9." This shows the understanding that Julian dates corresponding to future Julian periods are expected to be counted from the current epoch, without resetting. --Amble (talk) 16:18, 16 July 2024 (UTC)

Could you find a specific citable source for no-reset? I'm uncomfortable citing the software, and I can't find the quote in McCarthy. Nyttend (talk) 21:44, 18 July 2024 (UTC)

The JPL Horizons On-Line Ephemeris System is software I guess but doesn't reset and uses the best ephemerides known to man (same ones the Astronomical Almanac uses) Sagittarian Milky Way (talk) 01:46, 19 July 2024 (UTC)

I'd recommend going with the McCarthy article and/or the IAU resolutions from 1997. For McCarthy, look in the last paragraph, just before the acknowledgements, pg. 330. [3] For the IAU resolutions, look at resolution B1 and the appendix here: [4]. --Amble (talk) 16:12, 19 July 2024 (UTC)