Accuracy

Accuracy of Delphi 1.02 / astrolib 1.02

This document aims to give a detailed account of the accuracy of Delphi. Three charts have been calculated using Delphi 1.02 in combination with astrolib 1.02. 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.

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 1.02 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' 19 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 1.02 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 1.02 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.