Accuracy of Delphi 1.20 / astrolib 1.03
by Delphi Twentine
Web page formatting and a link modified by Apollia
This document aims to give a detailed account of the accuracy of Delphi.
Three charts have been calculated using Delphi 1.20 in combination with
astrolib 1.03.
The reference data has been obtained from the free chart service
of Astrodienst (www.astro.ch),
whose calculations are based on JPL (NASA) data.
Chart 1: Paris 1982
Chart 2: Melbourne 1955
Chart 3: Rome 800
General Comments
Planetary positions are calculated with an accuracy of the order of one arc minute for dates less than a century away from now.The position of Pluto is calculated from a numerical fit to its orbit, which seems to be optimized for the 20th century. Outside this range, precision deteriorates more quickly than for the other objects.
The position of the true moon node is of the order of 5 times less precise than the position of the moon. The largest error I have seen in the 20th century was 10'.
Time zones are calculated from UNIX time zone data, which ranges back to dates when countries observed local mean time. There are about 350 UNIX time zone locations, plus about 2000 additional locations (recognizable by the dimmed clock symbol in Delphi) of which each one has been assigned to one of the UNIX time zone locations. The data for the additional locations has been collected as follows.
For US locations, latitiude and longitude have been electronically extracted from the US 1990 Census data and time zones have been determined from the 1995 Rand McNally Road Atlas in combination with UNIX location comments. For non-US locations, latitude and longitude have been entered manually from paper sources, then plotted and verified visually in order to exclude any gross errors. Time zones have been determined from various maps in combination with UNIX location comments.
Please refer to astrolib's documentation and source code for further information.
Chart 1
Paris (France), 15 May 1982, 10.55 am local time| Item | Astrodienst (www.astro.ch) | Delphi+astrolib 1.03 | Difference |
|---|---|---|---|
| Longitude | 2e20 | 2e20 | 0' |
| Latitude | 48n52 | 48n52 | 0' |
| Time Zone | +2 | +2 [CEST] | 0 min |
| Sun | 24 Tau 12'06" | 24 Tau 13' | 1' |
| Moon | 14 Aqu 38'14" | 14 Aqu 37' | 1' |
| Mercury | 13 Gem 51'26" | 13 Gem 52' | 1' |
| Venus | 12 Ari 12'46" | 12 Ari 14' | 1' |
| Mars | 00 Lib 27'37" | 00 Lib 27' | 1' |
| Jupiter | 03 Sco 05'16" r | 03 Sco 05' r | 0' |
| Saturn | 16 Lib 25'39" r | 16 Lib 25' r | 1' |
| Uranus | 02 Sag 59'03" r | 02 Sag 59' r | 0' |
| Neptune | 26 Sag 29'43" r | 26 Sag 30' r | 0' |
| Pluto | 24 Lib 45'45" r | 24 Lib 46' r | 0' |
| True Moon Node | 14 Can 31'30" | 14 Can 34' | 4' |
| Ascendent | 01 Leo 07' | 01 Leo 08' | 1' |
| Midheaven | 09 Ari 38' | 09 Ari 38' | 0' |
| Placidus 2nd | 18 Leo 33' | 18 Leo 35' | 2' |
| Placidus 3rd | 10 Vir 18' | 10 Vir 19' | 1' |
| Placidus 11th | 18 Tau 15' | 18 Tau 16' | 1' |
| Placidus 12th | 28 Gem 47' | 28 Gem 48' | 1' |
| Koch 2nd | 23 Leo 59' | 23 Leo 59' | 0' |
| Koch 3rd | 16 Vir 44' | 16 Vir 44' | 0' |
| Koch 11th | 03 Gem 54' | 03 Gem 55' | 1' |
| Koch 12th | 06 Can 21' | 06 Can 21' | 0' |
Chart 2
Melbourne (Australia), 6 October 1955, 10.01 pm local time| Item | Astrodienst (www.astro.ch) | Delphi+astrolib 1.03 | Difference |
|---|---|---|---|
| Longitude | 144e58 | 144e58 | 0' |
| Latitude | 37s49 | 37s49 | 0' |
| Time Zone | +10 | +10 [EST] | 0 min |
| Sun | 12 Lib 27'24" | 12 Lib 28' | 1' |
| Moon | 14 Gem 57'17" | 14 Gem 59' | 2' |
| Mercury | 27 Lib 08'04" r | 27 Lib 08' r | 0' |
| Venus | 21 Lib 51'52" | 21 Lib 53' | 1' |
| Mars | 25 Vir 32'25" | 25 Vir 33' | 1' |
| Jupiter | 24 Leo 09'10" | 24 Leo 10' | 1' |
| Saturn | 19 Sco 04'41" | 19 Sco 05' | 0' |
| Uranus | 01 Leo 51'00" | 01 Leo 49' | 2' |
| Neptune | 27 Lib 23'52" | 27 Lib 24' | 0' |
| Pluto | 27 Leo 52'43" | 27 Leo 53' | 0' |
| True Moon Node | 19 Sag 40'22" r | 19 Sag 36 [*] | 4' |
| Ascendent | 26 Tau 09' | 26 Tau 09' | 0' |
| Midheaven | 07 Pis 56' | 07 Pis 57' | 1' |
| Placidus 2nd | 26 Gem 48' | 26 Gem 48' | 0' |
| Placidus 3rd | 01 Leo 57' | 01 Leo 57' | 0' |
| Placidus 11th | 09 Ari 23' | 09 Ari 24' | 1' |
| Placidus 12th | 04 Tau 54' | 04 Tau 54' | 0' |
| Koch 2nd | 22 Gem 59' | 22 Gem 59' | 0' |
| Koch 3rd | 24 Can 38' | 24 Can 39' | 1' |
| Koch 11th | 04 Ari 09' | 04 Ari 10' | 1' |
| Koch 12th | 00 Tau 18' | 00 Tau 18' | 0' |
Chart 3
Rome (Italy), 25 December 800, noon local time (Julian Calendar)| Item | Astrodienst (www.astro.ch) | Delphi+astrolib 1.03 | Difference |
|---|---|---|---|
| Longitude | 12e29 | 12e29 | 0' |
| Latitude | 41n54 | 41n54 | 0' |
| Time Zone | +0:49:56 | +0:50 [LMT] | 0 min |
| Sun | 08 Cap 27'55" | 08 Cap 24' | 4' |
| Moon | 22 Pis 31'18" | 22 Pis 27' | 4' |
| Mercury | 14 Sag 53'08" | 14 Sag 49' | 4' |
| Venus | 02 Sag 10'06" | 02 Sag 06' | 4' |
| Mars | 20 Lib 19'07" | 20 Lib 14' | 5' |
| Jupiter | 09 Pis 33'49" | 09 Pis 31' | 3' |
| Saturn | 00 Vir 50'31" r | 00 Vir 47' r | 4' |
| Uranus | 26 Lib 31'32" | 25 Lib 26' | 1 deg 6' |
| Neptune | 10 Lib 27'52" | 11 Lib 05' | 37' |
| Pluto | 06 Aqu 26'06" | 10 Aqu 50' | 4 deg 24' |
| True Moon Node | 05 Cap 18'09" r | 05 Cap 20' [*] | 2' |
| Ascendent | 14 Ari 05' | 14 Ari 03' | 2' |
| Midheaven | 07 Cap 15' | 07 Cap 14' | 1' |
| Placidus 2nd | 21 Tau 55' | 21 Tau 53' | 2' |
| Placidus 3rd | 16 Gem 31' | 16 Gem 30' | 1' |
| Placidus 11th | 29 Cap 13' | 29 Cap 12' | 1' |
| Placidus 12th | 28 Aqu 18' | 28 Aqu 17' | 1' |
| Koch 2nd | 19 Tau 25' | 19 Tau 23' | 2' |
| Koch 3rd | 16 Gem 07' | 16 Gem 06' | 1' |
| Koch 11th | 01 Aqu 56' | 01 Aqu 55' | 1' |
| Koch 12th | 04 Pis 40' | 04 Pis 38' | 2' |
[*] Delphi does not calculate whether the true moon node is retrograde.