Because of the Earth's tilt on its axis, the declination of the Sun varies systematically throughout the year.
| Date | Declination of Sun |
| Mar 21st | 0 degrees |
| Jun 21st | +23.5 degrees |
| Sep 21st | 0 degrees |
| Dec 21st | -23.5 degrees |
Therefore, the path that the Sun takes across the sky varies through the year. Here is what happens in Ithaca:
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On June 21st, the Sun is at its highest declination, +23.5 degrees. The path of the Sun on that day is longest, so the length of the daylight hours is longest. |
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| Can you figure out what happens on Mar 21st and Sept 21st? | |
On Dec 21st, the Sun is at its lowest declination, -23.5 degrees. The path of the Sun on that day is shortest, so the length of the daylight hours is shortest. |
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This means that the noontime altitude of the Sun is different at different times of the year. The Sun transits the meridian at a higher altitude in the summer than in the winter.
