The solar constant is **a measure of the solar electromagnetic radiation available per square meter at the Earth’s distance from the sun.** It quantifies the rate at which energy is received on a unit surface, such as a solar panel. In this context, the constant represents the total radiant energy from the sun that is absorbed at a specific location. It also finds applications in various atmospheric and geological sciences.

Despite being referred to as a constant, the solar constant is relatively constant, with a **variation of about 0.2%** in a cycle that peaks approximately every eleven years. The first estimation of this constant was made by Claude Pouillet in 1838 at 1.228 kW/m². Currently, the constant is rated at approximately 1.361 kW/m² during a solar minimum and around 1.362 kW/m² during a solar maximum.

**Calculating Solar Constant**

This constant represents the total spectrum of electromagnetic radiation, not limited to visible light alone, and **is measured using direct satellite observations.** Its calculation involves the utilization of the Stefan-Boltzmann constant, which is related to the power per unit area emitted by a black body based on its thermodynamic temperature.

**The dimensional formula for this constant is as follows:**

Solar constant = Energy / (Unit area x Unit time)

= ML²Tâ»² / (L²T)

= MTâ»³

The formula indicates that **this constant has dimensions of mass (M) divided by time (T) cubed**, which represents the incident solar energy per unit area per second on the Earth’s surface.

**Must Read:** What is Solar Radiation?