‘Equal’ days and nights call for some Arizona latitude

Hey, guess what? I’m sitting here wearing my baseball cap sideways, and there’s nothing you can do about it, no matter how many assistant principals you bring along.

Hoo-ha.

OK, enough madcap hijinks. There is work to do. This is the question:

On Monday sunset was listed at 6:37 p.m. and sunrise at 6:37 a.m. Why were the day and night of the same length then, but not today, which is the spring equinox?

First of all, the sunrise-sunset chart I looked at said sunrise Monday was 6:39 a.m. and sunset at 6:36 p.m.

That is neither here nor there. The point is that today at 11:49 p.m. our time the geometric center of the sun’s disk crosses the equator and the day and night are, in theory, of equal length.

Of course, the sun isn’t really going anywhere and it is us spinning and orbiting and tilting.

Anyway, at the equinox the sun is directly over the equator and “moving” north and from now until the summer solstice the days will be getting longer.

So, today’s sunrise is 6:34 a.m. and sunset is 6:39 p.m., not exactly an even split. The closest we came was Tuesday when the sun came up at 6:38 a.m. and set at 6:37 p.m. Why aren’t day and night equal today?

The answer is latitude, according to the U.S. Naval Observatory:

“At higher latitudes in the northern hemisphere, the date of equal day and night occurs before the March equinox.

“In the northern hemisphere, at latitude 5 degrees the dates of equal day and night occur about Feb. 25 and Oct. 15; at latitude 40 degrees they occur about March 17 and Sept. 26. On the dates of the equinoxes, the day is about 7 minutes longer than the night at latitudes up to about 25 degrees, increasing to 10 minutes or more at latitude 50 degrees.”

Phoenix is at latitude N33, so between the 5-degree thing and the 40degree thing, you can kind of figure it out for yourself.