Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Chuckknorris420 on 15/08/2017 08:39:29

Title: Is the sun in the same spot each year?
Post by: Chuckknorris420 on 15/08/2017 08:39:29

From one spot on earth does the sun move across the sky in the same path on the same day each year?

Say is the sun in the same spot in the sky at 12:00 noon on the 15th of August every year?

Thanks for the help

Title: Re: Is the sun in the same spot each year?
Post by: Colin2B on 15/08/2017 10:12:50

Within practical accuracy, and from year to next, the answer is yes. Over time there are small changes due to shift of the earth's tilt etc. Remember the solar year and calendar year are not the same so leap years make a 1/4 degree shift each year.
If you want to know the path with extreme accuracy and have the instruments to check, there are tables you can use to calculate the apparent position ie allowing for aberration.

Title: Re: Is the sun in the same spot each year?
Post by: evan_au on 15/08/2017 11:32:43

Sundials use the fact that the Sun follows the same path every year.

There is a small figure "8" inscribed on the sundial, which tells you how many minutes to advance or retard the sundial indication, for a given date in the year.

This figure 8 comes about because the Earth's orbit around the Sun is elliptical, so at certain times of the year, the Sun will be at its highest a few minutes before or after 12:00.

See: https://en.wikipedia.org/wiki/Analemma#Solar_analemma_as_seen_from_Earth

The Milankovitch cycles (https://en.wikipedia.org/wiki/Milankovitch_cycles) represent slow changes in Earth's axis and orbit, so the analemma would need to be updated every century or so.