What is the solar constant, and what is its approximate value?

What is the solar constant, and what is its approximate value?

• A. The average solar energy received per unit area at Earth's top of atmosphere, about 1361 W/m^2.
• B. The energy per square kilometer from sun at Earth's surface.
• C. The maximum solar energy at noon.
• D. The amount of solar energy reaching the moon.

Answer: (A)

The solar constant is the solar irradiance that would be received by a surface normal to the Sun’s rays at Earth’s distance from the Sun, measured at the top of the atmosphere. Its approximate value is about 1361 W per square meter (often rounded to 1.36 kW/m^2). This value is a standard reference for energy balance calculations because it represents the amount of solar energy available before any atmosphere or geometry reduces it. It’s not the energy that actually makes it to Earth's surface (the atmosphere and the angle of sunlight reduce it), nor is it the maximum noon value on the ground, or the energy reaching the Moon.

The solar constant is the solar irradiance that would be received by a surface normal to the Sun’s rays at Earth’s distance from the Sun, measured at the top of the atmosphere. Its approximate value is about 1361 W per square meter (often rounded to 1.36 kW/m^2). This value is a standard reference for energy balance calculations because it represents the amount of solar energy available before any atmosphere or geometry reduces it. It’s not the energy that actually makes it to Earth's surface (the atmosphere and the angle of sunlight reduce it), nor is it the maximum noon value on the ground, or the energy reaching the Moon.