Equation of time and length of solar day

The Equation of Time is the difference between the time determined by a sundial and the clock time. It is due to the obliquity of the Earth's axis and the unequal motion of the Earth around the Sun (ellipse). The value, computed for 12:00 UT, is between -14 :20 min (near Feb 12) and +16:24 min (near Nov 4).


equation of time diagram graph Diagram by my Planets Applet (using "Write/Draw" menu)
 
Sun Declination & Equation of Time


The length of the current solar day (i.e. the time interval between culmination of the Sun on prev. and curent day) is not exactly 24 hours; the difference is given in brackets (e.g. +18.8 s).

For 2001:


equation of time
length of solar day
Jan 1
- 03:45 min
24 h - 28.3 s
15
- 09:34 min
24 h - 21.2 s
Feb 1
- 13:38 min
24 h - 08.1 s
15
- 14:07 min
24 h + 02.8 s
Mar 1
- 12:18 min
24 h + 11.6 s
15
- 08:51 min
24 h + 16.8 s
Apr 1
- 03:48 min
24 h + 17.9 s
15
+ 00:02 min
24 h + 14.6 s
May 1
+ 02:57 min
24 h + 07.3 s
15
+ 03:40 min
24 h - 00.6 s
Jun 1
+ 02:09 min
24 h - 09.1 s
15
- 00:31 min
24 h - 12.8 s
Jul 1
- 03:53 min
24 h - 11.6 s
15
- 05:59 min
24 h - 06.2 s
Aug 1
- 06:18 min
24 h + 03.6 s
15
- 04:24 min
24 h + 11.7 s
Sep 1
+ 00:06 min
24 h + 18.9 s
15
+ 04:55 min
24 h + 21.4 s
Oct 1
+ 10:26 min
24 h + 19.4 s
15
+ 14:17 min
24 h + 13.4 s
Nov 1
+ 16:24 min
24 h + 01.7 s
15
+ 15:20 min
24 h - 10.0 s
Dec 1
+ 10:50 min
24 h - 22.3 s
15
+ 04:41 min
24 h - 28.8 s

equation of time table

Equation of Time table by my Planets Applet (use "Write/Draw" menu")

Web Links

Equation of Time (Royal Greenwich Observatory Information Leaflet)

Sundials on the Internet - the Equation of Time

Equation of Time -- Problem in Astronomy (M. Müller)

Die Zeitgleichung - Eine einfache Formel zu Sonnenaufgang und Untergang