[divyanshisingh987456321]

• Closes offer "geometric/analytic" solar positions as method/how in get_solarposition #2914
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• Tests added
• Updates entries in docs/sphinx/source/reference for API changes.
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Adds pvlib.solarposition.geometric, a fast but approximate solar position calculation, and makes it available as method='geometric' in get_solarposition, as requested in #2914.

Approach

• Declination and equation of time come from the Spencer (1971) series (declination_spencer71, equation_of_time_spencer71).
• Zenith and azimuth come from the existing solar_zenith_analytical and solar_azimuth_analytical.
• Atmospheric refraction is neglected, so apparent_zenith and apparent_elevation equal zenith and elevation. This is stated in a warning in the docstring.
• The hour angle is wrapped to [-180, 180) degrees before computing the azimuth, since the azimuth branch depends on its sign.
• Timezone-naive times are treated as UTC, as in ephemeris.

Accuracy: compared with spa_python hourly over all of 2026 at four sites (Golden, Gurugram, Sydney, Tromsø). The maximum zenith difference was about 0.6 degrees and the maximum daytime azimuth difference about 1 degree.

Tests added in tests/test_solarposition.py: comparison with SPA at the four sites above, output columns and ranges, naive times treated as UTC, and dispatch through get_solarposition.

Open design questions (also asked in #2914):

• Is method='geometric' the right interface, or should it be something else?
• Should geometric be a public function like ephemeris, or private?
• Should the apparent_* columns be returned, or omitted since refraction is neglected?

I used an AI assistant (Claude) to help draft this change. I reviewed the code, ran the tests locally and take responsibility for it.

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