There are people taking it for granted they already know how the Sun moves.  The trouble with this is what they think they know is false.  As I have pointed out before they may believe the Sun’s rising and setting to be in the same direction year-round.  This is only precisely correct if one is on the very Equator.  The further one gets from the Equator the larger is the difference over the year.  Naturally the Sun moves in the same direction the entire year.  The direction it rises and sets can in contrast differ much.

Maybe it is a good idea to explain certain expression.  That the Sun is up means it is visible above the horizon.  Or at least would be this if just the roundness of Earth was in the way.  It is enough if just a little of the Sun would be visible if the horizon was clear.  Solstices consist of the dates when the time with this is the most extreme.  Equinoxes are the dates when day and night is equally long everywhere.  There are two equinoxes and solstices every year.  Exactly which dates they are varies from year to year.  Printed almanacs use to state which dates they are.

I myself grew up in Stockholm or more exactly in the suburb of Kista.  There it is a drastic difference in how long the Sun is up.  It is up about three times as long at midsummer as shortly before Christmas.  Does the Sun move three times as fast when the day is the longest?  If so, sundials would not work.  My own experience make me understand the Sun does not rise and set in the same directions year-round.  It does not even rise and set in approximately the same directions.  The differences in daylight over the year are for too large for that.

The distance from Equator to pole is graded in 90 degrees of latitudes.  On the very Equator day and night are equally long the whole year.  When one moves away from the Equator the differences gradually increase along an even curve.  Here are some examples of how large the differences are:

5° • 36 minutes – Aba (Nigeria), Makassar, Teresina.

10° • 1 hour, 10 minutes – Can Tho, Cochin, San José (Costa Rica).

15° • 1 hour, 47 minutes – Korat, Lubango.

20° • 2 hours, 26 minutes – Chandrapur, Haikou, Serra (Brazil).

25° • 3 hours, 7 minutes – Karachi, Kunming, Taipei.

30° • 3 hours, 52 minutes – Cairo, New Orleans, Porto Alegre.

35° • 4 hours, 43 minutes – Albany (Australia), Albuquerque, Kyoto.

40° • 5 hours, 41 minutes – Ankara, Peking, Philadelphia.

45° • 6 hours, 51 minutes – Belgrade, Minneapolis, Turin.

50° • 8 hours, 18 minutes – Kharkiv, Prague, Winnipeg.

55° • 10 hours, 12 minutes – Chelyabinsk, Derry, Newcastle (UK).

60° • 13 hours, 0 minutes – Oslo, Saint Petersburg (Russia).

65° • 18 hours, 29 minutes – Oulu.

The times I have stated are for the northern hemisphere.  (What I state for 5° is moreover my educated guess.)  However, I think it is the same in the southern one.  Anyway, the Sun moves at approximately the same pace over the sky.  Which time of the year it is does not make much of a difference.

At 66½ degrees are the polar circles.  There the Sun does not set at all on the summer solstice.  When it reaches the horizon in the middle of the night it instead turns upwards.  This is called midnight Sun since it is up all night.  The price of this is polar night.  Just a little closer to the pole the sun does not rise on the winter solstice.  There of cause is some twilight when it is in the middle of the day.  But then it gets dark again without the Sun having risen.

The closer to the pole one gets the longer the periods without sunrise or sunset gets.  On the very poles the Sun is up about six months in a row.  The periods of dusk and dawn lasts for several weeks.  Please note this only applies on the North and South Poles themselves.  The rest of the Polar Regions have different degrees of midnight Sun and polar night.  The periods when they happen are moreover symmetrical.  If anything the time with midnight sun is somewhat longer than the one with polar night.  This is because the light of heavenly bodies bends a little at the horizon.

In additions there are differences in how high the Sun can be.  When a heavenly body is 90 degrees up it is called being in zenith.  On the Equator the Sun reaches zenith on both equinoxes.  Does one get a little closer to the poles the two dates are moved to two dates closer to the summer solstice.  The further one gets from the Equator the closer to each other do they get.  At 23½ degrees are the Tropical circles.  At those the Sun only is in zenith on the summer solstice.  Further from the Equator than this the Sun can’t.  In contrast one can calculate how high the Sun can be.  One starts from 90 and subtracts one’s latitude.  Afterwards one adds 23½.  Then one gets about as high as the Sun can be where one is.  However, this only applies on the summer solstice.  For the winter solstice one subtracts one’s latitude and afterwards subtracts 23½.

Finally I want to warn there are severely misleading formulas.  An American misunderstood the tilt of Earth’s axis against the plane of its orbit.  It differs 23½ degrees from a right angle.  He thought the Sun’s rising and setting never diverges from cardinal directions more than precisely that.  The continuous US is 24 – 49 degrees north.  The time the Sun is up varies by 3 – 8 hours.  If one hour equals 15 degrees this gives 23 – 60 degrees of divergence.  Normal variation was misinterpreted as something having suddenly changed.  Something he unfortunately was not alone about.


Uploaded on the 2nd of May 2024.