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I've seen the standard epoch described as both J2000 and J2000.0. Is there any difference between the two designations?

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  • $\begingroup$ They're identical.See en.wikipedia.org/wiki/Epoch_(astronomy)#Julian_years_and_J2000 "J2000 = JD 2451545.0 (TT)" $\endgroup$
    – PM 2Ring
    Jan 9, 2023 at 14:20
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    $\begingroup$ They are the same. It is possible for an epoch ending with a fractional amount, which is why some people put the .0 there. E.g. the Hipparcos catalog's epoch is J1991.25, which indicates a fraction of a year. $\endgroup$ Jan 9, 2023 at 15:24
  • $\begingroup$ Also some of the Gaia data releases have non .0 epochs e.g. DR2 has the reference epoch of J2015. 5 $\endgroup$ Jan 9, 2023 at 16:10

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They're identical. See https://en.wikipedia.org/wiki/Epoch_(astronomy)#Julian_years_and_J2000 "J2000 = JD 2451545.0 (TT)" - PM 2Ring

They are the same. It is possible for an epoch ending with a fractional amount, which is why some people put the .0 there. E.g. the Hipparcos catalog's epoch is J1991.25, which indicates a fraction of a year. - Greg Miller

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