Re: [Phys-L] solar constant

[brian whatcott <betwys1@sbcglobal.net>]

There are two easily internet-accessible low-cost experiments: both of 
them use a weighed mass of water's change of state as a heating measure.
The first uses a foam cup half filled with water which is frozen, then 
equilibrated to 0degC and drained  before being irradiated onto a black 
disk cover (a second cup with a silver disk is used as a differential 
sample.) The amount of water melted is weighed. (This write-up is a 
rerun of Eaton, DeGeer, Freir Pysics & Astronomy, U Minn (1977) thanks 
to Greenslade at Kenyon as Column editor of The Physics Teacher

http://tinyurl.com/pmyksr7

The second method described by Wolfe at  U New South Wales, Sydney Aus. 
(with several other experiments)  uses  a measured mass of water in an 
aluminum foil tray painted black,  preferably of known initial 
temperature, and timed to the point of total evaporation.

http://tinyurl.com/oyu28lc


You would expect them to show a surface constant around 700 Watts/meter 
squared.

Sincerely

Brian Whatcott   Altus OK Indian Territory.

On 5/21/2014 9:20 AM, Richard Tarara wrote:
> The 1370 W/m2 is at the top of the atmosphere.  From Jerry Marion's 
> 'Energy in Perspective':  "At the top of the atmosphere, solar energy 
> is incident at an average rate of approximately 1.4 kW/m2. The total 
> amount of energy received by the Earth from the Sun in a year amounts 
> to 1.6x10^18 kWh. Because of the absorption in the atmosphere and 
> reflection from clouds, only about half of the incident energy reaches 
> the surface of the Earth, and averaged over a day, the solar power is 
> about 0.2 kW/m^2."
>
> At any particular moment the irradiance at the surface is going to 
> depend on the day of the year, the hour of the day, and of course the 
> weather conditions.  I suspect there are tables and know there are 
> 'days of sunshine' tables by location.
>
> rwt
>
>
>
>
> On 5/21/2014 10:04 AM, Anthony Lapinski wrote:
> > The solar constant is around 1370 W/m2. I believe this is the average
> > value over the entire Earth in one year. I have two questions.
> >
> > 1. How can I find the approximate value on a given day at a given 
> > location
> > (latitude)? Is there some formula or way to estimate? I realize this 
> > might
> > not be easy.
> >
> > which leads to:
> >
> > 2. Is there a "simple" experiment kids can do to measure the solar
> > constant (solar cell, heating water, etc.)?
> >
> > This has some good concepts for energy, heat, and optics in both physics
> > and astronomy.
> >
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