Is the longest day adjacent to the shortest night?

Question

My dad has insisted for years that it isn't. When I ask him to explain he says "it's the obliquity of the elliptic" and that's as far as I get.

Note to the drongo 2-point collectors: yes I KNOW that day and night are not the same as each other!

Answer 1

I'm not sure what he means by his explanation, but he's not totally off to think there would at least be a possibility of the longest 'day' not being adjacent to the shortest 'night'.

As measured from the Sun's local zenith to the next local zenith, solar days are not the same length of time (24 hours is just the average amount of time to get from noon to noon). It takes longer to get from local noon to the next local noon at the solstices when the Earth is tilted directly toward or directly away from the Sun. The shortest solar days (noon to noon) should be at the equinoxes. (In other words, if there are more total seconds in the solar day at the solstice, then having the most daylight seconds doesn't necessarily mean having the shortest night time seconds).

Additionally, the Earth's orbit is slightly elliptical. At perihelion (closest point to the Sun), the Earth is traveling faster and sweeping out a bigger angle per second. That means the Earth has to rotate further to get back to noon the next day. Solar days near perihelion are longer while solar days near apohelion (furthest from Sun) are shorter. This is where your dad's argument starts to break down. The Earth is at apohelion around the first week of July and at perihelion the first week of January. In other words, there are more seconds in a solar day in the winter than there are in the summer. The tilt of the Earth is more significant, so there are still more seconds in a solar day near the summer solstice than either equinox, even if the longest solar day (noon to noon) isn't in the summer.

The biggest reason his argument breaks down is sheer magnitude. The variation in the length of a solar day is in seconds/day while the difference in the amount of daylight/darkness can be minutes/day (the amount of variation depends on a person's latitude)

For 2006, the longest daytime period will be on Jun 21, with the shortest nightime period being Jun 20 or 21 (the Naval Observatory's charts only list hours and minutes).

Answer 2

Since there are 24 hours in a day on Earth the longest day must also be associated with the shortest night.

As an aside, the longest day in the Northern Hemisphere will be the same as the shortest day in the Southern Hemisphere.

Answer 3

The longest day means litteraly the highest path the sun takes in the sky, leading to the longest daylight hours and thusly the shortest dark hours. So - yes.

Answer 4

The longest day and shortest night almost by definition must coincide.

But the longest day and earliest sunrise do not coincide because the earth is moving around the sun (by about 1/365 of its orbit per day).

See the link.

Answer 5

Yes, in fact the longest day is adjacent to the shortest night.

Answer 6

By adjacent to you mean same 24 hour period?
Each day is 24 hours total.
1 day = 24 hours = total daylight hours (Hd) + total night hours (Hn).
Since night hours (Hn) = 24 - Hd, it becomes obvious that the Hn decreases proportionally as Hd increase.
Therefore, the longest day must have the shortest night.

Answer 7

Yes

Answer 8

Yes

Answer 9

I think so. Because there are only 24 hours in the day, logic suggests that if there are more hours in the day, then there are less hours at night. Sounds like either your dad is really really clever or he's just trying to be!

Answer 10

When we had the longest day in the northern hemisphere on June 21st, we also had the shortest night. That is a very dumb question.