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Sun Position Calculations

Sun Position Calculations. Paul Calder Flinders University. Declination. If orbit was circular -23.45 cos(360/365 * (N+10)) Since orbit is actually (slightly) elliptical, use 3rd order harmonic year angle (  degrees) = N * 360/365

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Sun Position Calculations

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  1. Sun Position Calculations Paul Calder Flinders University

  2. Declination • If orbit was circular -23.45 cos(360/365 * (N+10)) • Since orbit is actually (slightly) elliptical, use 3rd order harmonic year angle ( degrees) = N * 360/365 declination ( degrees) = 0.39637 - 22.9132 cos  + 4.02543 sin  - 0.38720 cos 2 + 0.05197 sin 2 - 0.15453 cos 3 + 0.08490 sin 3

  3. Hour Angle • Timezone offset • 12 noon is not "high noon" • Equation of time • Compensate for elliptical orbit • Compensate for axial tilt • Hour angle • H = time + TZO + EOT

  4. Timezone Offset • Where is CST "correct"? • What longitude? • What towns are nearest? • When is ASMS "local solar noon"? • Should Adelaide switch to TZ+10? • What other parts of the world have half-hour timezones?

  5. The Equation of Time 0.017189 + 0.428108 cos  - 7.351407 sin  - 3.349466 cos 2 - 9.361774 sin 2 http://www.analemma.com/

  6. Converting Coordinates input: latitude  declination  hour angle H calculate sin a = sin  sin  + cos  cos  cos H = P cos A cos a = cos  sin  – sin  cos  cos H = Q sin A cos a = -cos  sin H = R azimuth (A) = atan2(Q, R) altitude (a) = atan2( sqrt(Q*Q + R*R), P)

  7. Your Turn! • Compute the sun position from the front door of ASMS at 10am on May 10 • Using your calculator • Check using the spreadsheet • Compare with on-line calculators

  8. Next Week

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