The Solar Constant– a term which I was introduced to in one of my Physics classes this year. I had known how to calculate the Luminosity of stars at the time. Using my knowledge on the brightness of stars, I was able to figure out the way to calculate the Solar constant online.
The Solar Constant is basically the figure of the amount of heat reaching the surface of the Earth within a given area, whose unit is the same as intensity (W/m^2). It has a value of about 1400 W/m^2. In order to calculate the intensity of light of a source (in this case, the Sun), its Luminosity must be known before-hand. But, in astronomy, this is rarely the case. Instead, what we know of a source of light (typically a star) is its Apparent Brightness!
This Apparent Brightness is nothing but the intensity of light reaching to us! Therefore, the apparent brightness of the Sun is in fact the value of the Solar Constant! The mathematical formula for apparent brightness is:
Brightness= L/4*π *(distance from the object)^2
We can use this formula to calculate the value of the Solar constant, because we know the Luminosity of the Sun, as well as our distance from the Sun to remarkable accuracy.
Solar Constant= 3.846*10^26 W/4*pi*(1.5*10^11 m)^2
or, S.C= 3.846*10^26 W/2.25*10^22 m^2*4*π
or, S.C= 0.1365*10^4
Solar Constant= 1365 W/m^2
It’s worth noting that the Solar Constant doesn’t remain the same. Small changes in Solar activity, as well as Earth’s revolution extremes results in subtle variations in the Solar Constant.
The Solar Constant is basically the figure of the amount of heat reaching the surface of the Earth within a given area, whose unit is the same as intensity (W/m^2). It has a value of about 1400 W/m^2. In order to calculate the intensity of light of a source (in this case, the Sun), its Luminosity must be known before-hand. But, in astronomy, this is rarely the case. Instead, what we know of a source of light (typically a star) is its Apparent Brightness!
This Apparent Brightness is nothing but the intensity of light reaching to us! Therefore, the apparent brightness of the Sun is in fact the value of the Solar Constant! The mathematical formula for apparent brightness is: Brightness= L/4*π *(distance from the object)^2
We can use this formula to calculate the value of the Solar constant, because we know the Luminosity of the Sun, as well as our distance from the Sun to remarkable accuracy.
Solar Constant= 3.846*10^26 W/4*pi*(1.5*10^11 m)^2
or, S.C= 3.846*10^26 W/2.25*10^22 m^2*4*π
or, S.C= 0.1365*10^4
Solar Constant= 1365 W/m^2
It’s worth noting that the Solar Constant doesn’t remain the same. Small changes in Solar activity, as well as Earth’s revolution extremes results in subtle variations in the Solar Constant.
Bijaya's creations 