Talk:Tropical year

Naming conventions

Karl, lets settle on a convention about Latin, Greek, English words. I think we should stick to whatever is current in English. If you start to Romanize or Hellenize English words, there is no end - anglosaxons completely screw up foreign words; e.g.:

equinox would be aequinox (equus = horse, aequus = equal (sic!))

Homer would be Homeros

Now the English word is perihelium, not perihelion; like the stuff is helium, not helion. -- Tompeters

This would be a good argument, except for the fact that it's "perihelion" in English. What dictionary are you using that says otherwise? --Zundark, 2001 Oct 25

— Preceding unsigned comment added by Zundark (talk • contribs) 11:43, 25 October 2001 UTC

OK, I screwed up -- Tompeters — Preceding unsigned comment added by Conversion script (talk • contribs) Revision as of 15:51, 25 February 2002 UTC

Bad example: Helium ends in -ium because it was first found spectroscopically in the sun and they thought it was a metal: and metals get -ium or -um on the end e.g. Thorium, Hafnium, Aluminium, Neodymium, Molybdenum. If the naming convention for noble gases was followed strictly, Helium actually should be called Helion, though no-ones going to rename it at this late date - Malcolm Farmer

— Preceding unsigned comment added by Malcom Farmer (talk • contribs) 12:10, 25 October 2001

Thanx for pointing that out, I never noticed. Good to see someone writing Aluminium, americans usually say aluminum.— Preceding unsigned comment added by Conversion script (talk • contribs) Revision as of 15:51, 25 February 2002 UTC

Ephemeris Time

The article now says:

The time scale is Terrestrial Time (formerly Ephemeris Time) which is based on atomic clocks

I don't understand this. One could understand this as "Terrestrial Time was formerly called Ephemeris Time". This is not the case. Ephemeris Time is different from Terrestrial Time; and is not based on atomic clocks. Terrestrial Time is now used a lot where Ephemeris Time used to be used. But wouldn't the formulae be different in the past if they used Ephemeris Time in the past? Until someone who really understands this, sorts this out, I will delete the text in parentheses "(formerly Ephemeris Time)" -- Adhemar — Preceding unsigned comment added by 212.65.42.127 (talk • contribs) 09:34, 29 August 2005

You have some valid points. Although Terrestrial Time (TT) is based on atomic clocks, it is a uniform time just like Ephemeris Time (ET), which was defined relative to the motion of solar system bodies, especially the Sun and Moon. TT (1991) is the new name for Terrestrial Dynamical Time (TDT, defined 1976). It was renamed because TDT was not dynamical, i.e., it was not based on the motion of the solar system. ET was the time base used in all national ephemerides until 1983. The offset of TT from International Atomic Time (TAI) was intentionally chosen to be 32.184 s so that it would equal ET, and thus ET can be directly substituted for TT in most astronomical equations. This is indeed done by Jean Meeus in his "Astronomical Algorithms". I am replacing the objectionable phrase by "(formerly, Ephemeris Time was used instead)". — Joe Kress 03:20, August 30, 2005 (UTC)

Mean tropical year

$365.2421896698-6.15359\times 10^{-6}T-7.29\times 10^{-10}T^{2}+2.64\times 10^{-10}T^{3}$

Some values for the equation cited (in article);

T	Year AD BC	Length	Diff to T = 0, days	Diff to T = 0, seconds
-100	-8000	365.242 533 738 800	000.000 344 069 T =000	29.727562
-60	-4000	365.242 499 236 800	000.000 309 567 000	26.746589
-50	-3000	365.242 462 526 800	000.000 272 857 000	23.574845
-40	-2000	365.242 417 751 000	000.000 228 081 200	19.706216
-30	-1000	365.242 366 493 400	000.000 176 823 600	15.277559
-20	0	365.242 310 338 000	000.000 120 668 200	10.425732
-10	1000	365.242 250 868 800	000.000 061 199 000	5.287594
0	2000	365.242 189 669 800	000.000 000 000 000	0.000000
1	2100	365.242 183 515 745	-000.000 006 154 055	-0.531710
10	3000	365.242 128 325 000	-000.000 061 344 800	-5.300191
20	4000	365.242 068 418 400	-000.000 121 251 400	-10.476121
30	5000	365.242 011 534 000	-000.000 178 135 800	-15.390933
40	6000	365.241 959 255 800	-000.000 230 414 000	-19.907770
50	7000	365.241 913 167 800	-000.000 276 502 000	-23.889773
60	8000	365.241 874 854 000	-000.000 314 815 800	-27.200085
70	9000	365.241 845 898 400	-000.000 343 771 400	-29.701849
80	10000	365.241 827 885 000	-000.000 361 784 800	-31.258207
90	11000	365.241 822 397 800	-000.000 367 272 000	-31.732301
100	12000	365.241 831 020 800	-000.000 358 649 000	-30.987274

MBG02 (talk) 12:33, 24 April 2022 (UTC)