This week I saw a sunrise on the Badstrand on Schiermonnikoog. From the sea I saw the sun rise above the horizon. This was one of the most beautiful things I can remember ever seeing. But from what I’ve seen that should be impossible, right? The sun is between the tropics all year round, that is, to the south of us. The Badstrand is clearly on the north side of the island and I have seen the sun rise from the sea north of the island. How is it possible that I saw the sun rise in the northeast when it is really south of us?
Answer
“The sun is between the tropics all year round”… that’s a dangerous expression. The tropics are two circles on the Earth. So the Sun cannot stand between them. The latitudes between the tropics are those places on Earth from which the Sun can be seen passing at the zenith on no more than two days in the year. The tropics have absolutely nothing to do with wind directions. After all, they walk all around the Earth.
The Sun is also not south of us all the time. It rises in the east (north-east in summer, south-east in winter), reaches its highest height above the horizon in the south, and sets in the west in the evening (north-west in summer, south west in winter). At night the Sun is in the north, but below the horizon. That we see the Sun rotating around us is a result of the rotation, every 24 hours, of the Earth around its axis. Here in Flanders, the Sun rises only 17° above the southern horizon in the depths of winter, and stays above the horizon for about 8 hours. On July 21, the Sun is almost 4 pm above the horizon and reaches a maximum elevation of 63° above the southern horizon in the south.
Notice that 17 = 40 – 23, that 63 = 40 + 23,
Those 40 = 90 – our north latitude (50° approximately), and those 23, those are the 23° of the tropics.
Answered by
prof.dr. Paul Hellings
Department of Mathematics, Fac. IIW, KU Leuven
Old Market 13 3000 Leuven
https://www.kuleuven.be/
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