| Astrophysics (Index) | About |
The solar constant is the density of the Sun's flux (amount of EMR energy per unit of an area perpendicular to the direction of the EMR) when the flux approaches Earth, or precisely, after traveling 1 AU. The current typically-cited value is 1.361 kilowatts per meter², an average derived from measurements over roughly three decades. (In other words, 1.361 kilowatts is an average of the power of the Sun's EMR that would strike a square-meter solar panel aimed at the Sun, located 1 AU from the Sun.) Despite the word constant, the actual flux reaching us is not: because Earth's orbit is a bit eccentric, the flux actually hitting Earth atmosphere varies around this solar constant, currently varying roughly 7% over the course of each year. In addition, the power at 1 AU is higher solar maximum and lower at solar minimum. The value is a measurement of the long-term average.