The Sun · Physics
Irradiance
Say it: ih-RAY-dee-unss IPA: /ɪˈreɪdiəns/ noun
Irradiance: The power of light or other radiation arriving on a surface, for each square meter of that surface.
Hold a card square-on to the Sun and every square meter of it catches a certain flow of energy. Tilt the card and the same sunlight spreads over more area, so the irradiance on it falls.
- Example
- Above Earth's atmosphere, the Sun's irradiance averages about 1,361 watts per square meter.
- Why astronomers use it
- It sets how much energy sunlight delivers to planets, to solar panels and to Earth's climate.
- Tiny cosmic connection
- Over one eleven-year cycle measured from space, the Sun's total irradiance changed by only about a tenth of a percent.
Deep Space The Sun Physics
Where to check it
Written for Cool Moon Facts in its own words; the sources cover the same idea in more depth.