Equi-knocks

20 September 2016

During the Equinox, Day doesn’t equal Night equally.

The word “Equinox” means “equal night”, which I have repeated enough myself over the years. Even after having used the Date and Time data for years, including sunset and sunrise times, I failed to examine this claim for myself. Except that the date itself doesn’t happen to be the one on which the day and night are of equal length. At least, not necessarily.

I discovered this table in the back of the book Canada’s Stonehenge by Gordon R Freeman, almost as an afterthought. The Equinox occurs twice a year as the Sun appears to cross the Equator. At the Equator, day and night are about the same length throughout the year, however, for those of us at other latitudes, the particular date when the day and night are of equal length varies as follows:

Dates of Equalnights*

Latitude 

Northern Hemisphere

Southern Hemisphere

10°

20°

~ Feb 3-9

Feb 25-26

Mar 7-8

Mar 13-14

~ Nov 4-10

Oct 17-18

Oct 5-6

Sept 29-30

~ Apr 30-May 6

Apr 14-15

Mar 31-Apr 1

Mar 26-27

~ Aug 9-12

Aug 28-29

Sept 10-11

Sept 16-17

30°

40°

50°

Mar 15-16

Mar 16-17

Mar 17-18

Sept 26-27

Sept 25-26

Sept 25-26

Mar 23-24

Mar 23-24

Mar 22-23

Sept 18-9

Sept 19-20

Sept 19-20

60°

80°

Mar 17-18

Mar 17-18

Sept 24-25

Sept 24-25

Mar 22-23

Mar 22-23

Sept 19-20

Sept 20-21

90°

Sun rises ~ Mar 18, sets ~ Sept 24

Sun rises ~ Sept 20, sets ~ Mar 22

*Calculated for 0° longitude, A.D. 2000. SZM: March 20, Sept 22. Solstice: June 21, Dec 21

Thus, beginning Sept 20, where the Sun rises above the horizon at the South Pole for the season, we see Equalnight dates sweep until Sept 30.

The Equinox itself occurs Sept 22nd 14:21 UTC.

Happy equanimous days all.