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# Re: [Phys-L] solar constant

• From: Bill Nettles <bnettles@uu.edu>
• Date: Thu, 22 May 2014 08:41:24 -0500

The University of Nebraska-Lincoln has a project for generating astronomy applets: astro.unl.edu

The Simulations List and the NAAP Labs are very rich, and the ClassAction project has some interesting elementary level items.

Of particular interest to this topic is the Seasons Simulator: http://astro.unl.edu/naap/motion1/animations/seasons_ecliptic.html

You can choose the latitude of the observer, then cycle the Sun position through the year and see the local noon zenith angle change. Conversely, choose a day and move the observer to see the zenith angle change.

The relationship for the "day", latitude, and noon zenith angle is: Latitude = Zen. + declination, where
Latitude is >0 for north, <0 for south,
Declination is >0 for north of equator, <0 for south of equator
Zen. Is >0 if observer is north of Sun, <0 if observer is south of Sun

There are a variety of approximating functions for finding the declination of the Sun in this decade. I have an Excel spreadsheet arranged by day of the year (1 month per column) that I can email if you wish. I suggest you find a formula and use it as an excuse to exercise your programming muscles.

Above all, have Phun!

-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of Folkerts, Timothy J
Sent: Wednesday, May 21, 2014 1:27 PM
To: 'Phys-L@Phys-L.org'
Subject: Re: [Phys-L] solar constant

I thought I responded earlier, but it seem to have gotten lost.

The Wikipedia article on "insolation" has some good info (http://en.wikipedia.org/wiki/Insolation), including typical power at the top of the atmosphere and at ground level for different parts of the world.

Perhaps most surprising is that the location with the largest single day insolation (at the top of the atmosphere) is the South Pole! Although the sun never gets very high, 23.5 degrees = 40% max sunlight, and it shines 24 hr/day. (And, of course, the earth is closer to the sun for the southern hemisphere summer than for the northern hemisphere summer).

Tim Folkerts

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