in reply to [OT] Astronomical puzzling about daylight hours at different latitudes

From different viewpoints on the earth you'll look with a different angle at the sun. (Remember that Australians are standing "upside down" from your perspective ;)

While the sun can reach the zenith only in the tropics¹ at noon (your shadow is between your legs) the perceived curve will become always flatter when distancing from the equator.

This curve is always under the horizon at polar night and always above in polar summer. That's because the rotation axis of the earth has an inclination compared to the sun³

Even a flat horizon is practically perceived like the earth's body hiding the sun like a mountain ridge surrounding you in winter. But in summer the horizon "lowers" to a valley and you are subjectively the one standing on a mountain top.

That's a gradual effect from poles to equator.

The combined effect of flattened curve, "moving" horizon and definition of sun rise or sunset effect the calculation. ²

Plus the flatter the curve, the longer does the sun need to fully pass the horizon from one tip to the other.

I found a German website where you can play with coordinates and check all parameters. The graphics are nice at displaying the perceived curve.

https://www.datum-und-uhrzeit.de/?coordinates=true

I compared points near Berlin and Rome with "integer" coordinates

HTH :)

Cheers Rolf
(addicted to the Perl Programming Language :)
see Wikisyntax for the Monastery

¹) by definition!

²) it's even more complicated because of precession, nutation and uneven shape of the rotating potato ellipsoid we live on

³) more correctly the ecliptic, the plane in which earth is rotating around the sun

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Re^2: [OT] Astronomical puzzling about daylight hours at different latitudes
by LanX (Saint) on Sep 06, 2024 at 16:01 UTC
    FWIW: I found the English version of that website https://www.date-and-time.net/

    The graphics are pretty good, if you open the images directly you can play around with the parameters in the URL.

    From all effects discussed is earth's axial tilt of 23 degrees the main factor, all the others are marginal.

    Try winter solstice for the same latitude and you'll see how the days become shorter the closer you reach the north pole, till you have polar night.

    That's the opposite at summer solstice, days become gradually longer till you have polar day.

    Try the same location with different dates and you'll see how the curve is seemingly rising and dropping by 2*23° during the year. ( See Sun_path )

    Here the images for equinox in Rome,

    Note how the altitude at noon is exactly 90°- 52.5° (your latitude)

    That's why the curve when approaching the pole must become always flatter till it's a line

    Together with the variation of altitude of +- 23 ° during the year the curve is rising and falling from the horizon.

    Different curves = different sun hours for same latitude.

    Cheers Rolf
    (addicted to the Perl Programming Language :)
    see Wikisyntax for the Monastery

    Update

    I don't think the graphs are correct for the southern hemisphere. Sun should wander in the north.

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