The precise shifting positions of the rising and setting sun through the year is a phenomenon observed thousands of years ago. The ancient Egyptians aligned their buildings - especially the pyramids - in such a way that sunlight entered the deepest passages only on certain days of the year, such as the summer equinox. The ancient Aztecs did the same, and so did the builders of Angkor Wat, and even the Padmanabha Swamy Temple in Kerala.
While it is relatively easy for communities that have lived at a particular location for many years to accurately predict the play of sunlight and shadows in their buildings through the year, the trick is to figure out how this would change in different parts of the globe. Consider this excerpt from an astronomy website -
At 40°N latitude (Denver, Colorado / Beijing, China), the sun shifts 7° north. Since the sun's diameter equals 1/2 degrees, that means the sun has been traveling its own diameter (14 days x 1/2 degree = 7 degrees) northwards each day. At 60°N latitude (Fairbanks, Alaska / Siberia), the sun moves about 2 sun diameters or one degree daily.
How did they come to the conclusion that "the sun's diameter equals 1/2 degrees"? What exactly does this mean, especially when you consider the fact that the distance between the earth and the sun varies from summer to winter making it appear larger or smaller across the seasons?
Things get a little more complicated here. Yet all this has been figured out with such amazing accuracy that we have websites that map the position of the sun to any given location on earth, any time of the year.
What we see here is a sun-path polar chart superimposed on an image from Google Maps. Each point on this is worked out by feeding in the local latitude in relation to the elevation of the sun and the time of day, for that location. For instance, Noida located at approx 28°N would see the sun at an elevation of 62° from the horizon (90° - 28°) on equinox days (21 Mar., and 21 Sep.).
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| Solar Altitude (cc - Hartz ) |
This explains why cities located on or near the equator (eg., Singapore - 1.29°N) see very little variation in the position of the sun across seasons. So when a Singaporean stretches his neck to squint at the blazing sun right overhead on an equinox day, a Norwegian resident at the northern-most city in the world, Longyearbyne (78.22°N) would find the same mid-day sun hovering near the horizon all day!
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REFERENCES & LINKS
- https://www.timeanddate.com/sun/india/new-delhi?month=6&year=2021
- Noida coordinates - 28.5355° N, 77.3910° E
- TED Talk - https://www.youtube.com/watch?v=Xm13Kq_E1ik
- https://www.sunearthtools.com/dp/tools/pos_sun.php
- https://earthsky.org/astronomy-essentials/how-far-does-sun-move-on-your-horizon-each-day/
- Sun path - https://en.wikipedia.org/wiki/Sun_path
- https://www.syedshiyazmirza.com/2019/03/sree-padmanabhaswamy-temple-during.html
- https://www.atlasobscura.com/articles/five-ancient-sites-to-celebrate-the-spring-equinox
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