Do all points on the earth surface have with the same longitude the same day and night times, i.e. does the earth rotate around it's own axis with the same speed for all points on the same longitude?
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1$\begingroup$ The night is slightly shorter on a mountain summit. $\endgroup$– gerrit ♦Commented Jan 27, 2023 at 11:08
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$\begingroup$ Think about the circles of latitude. Does one close to the Equator seems the same length as one close to a pole? Do two points with the same longitude on these two small circles make a rotation in the same time? If the length is different and the time is the same, then their rotation speed is different. $\endgroup$– Jean-Marie PrivalCommented Jan 27, 2023 at 18:04
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2 Answers
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It is not as simple as Earth axis is not normal to our rotation plane around the Sun (ecliptic). Earth axis is tilted 23.4 degres (aprox):
Sunlight impact to Earth parallel (aprox) to the ecliptic, but our rotation axis is tilted. It seems that everypoint at the same meridian should have same daylight, but depends on lattitude. According to the figure above, someone at Venezuela should have same daylight that someone at Labrador (Canada), as they are in the same meridian.
But the fact is that, due to this tilting, they are not transitting the same time:
Point at a higher lattitude (Canada), in this case, it is exposed less time to the sun due to Earth tilting. This figure will be at North Hemisphere winter. Yellow line is representing path exposed to sunlight and light blue is path not exposed to sunlight.
This is a simple representation not considering Earth atmosphere. If we consider Earth atmosphere, everything is a little bit more complicated, as there are different dawn times. Check this link: https://en.wikipedia.org/wiki/Dawn
With the same example, today daylight looks like:
Hope it helps!
answered Jan 29, 2023 at 9:37
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You are asking if locations on Earth with the same longitude (East/West position) but different latitude (North/South position) have the same length of day. The answer is no.
At the equator, the length of day (from sunrise until sunset) is approximately 12 hours regardless of the time of year. At the northern hemisphere summer solstice, latitudes north of the Artic Circle have 24 hour sunlight. That is, the Sun never sets.
Thus, the length of day is dependent on the date and the latitude. The length of the day is not dependent on the longitude. The time of sunrise and sunset depend on the longitude though.
