Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

The average energy we receive from the Sun is 1,366 w/m^2, and this only varies by 0.1% from the activity peak to trough of its 11 year cycle. About 9% of the energy comes from wavelengths less than 400 nm. The 200-300 nm region varies on the order of a few percent, 150-200 nm by 10-20% and shorter regions by over 50% with maximums at the cycles peak activity. Energy above 400 nm is almost constant over the cycle. Why does solar energy variation over the Sun's activity cycle vary inversely with wavelength?

share|cite|improve this question

This must be due to the fact, that majority of visible spectra is emitted by whole sun surface, which have stable size & temperature.

While short-wave UV must be emitted by hotspots & bursts, number & size of which is not constant and varies in large range.

share|cite|improve this answer
BarsMonster: Plages dominate sunspots during solar max increasing UV, and the corona is more energetic during solar max increasing EUV and x-rays. Is that consistent with your idea? – Michael Luciuk Apr 6 '11 at 15:20

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.