How is sunlight measured?

Answer 1

Measurement Units:

The measurement of the power of sunlight emitted from the sun is called Radiant Flux and is measured in watts. The measurement of the perceived power of sunlight is called Luminous Flux and is measured in lumens. Lumans are directly related to candelas (or candlepower), which is the luminous intensity emitted in any one direction. Measurement Methods: Surprisingly, luminosity is still often measured by eye. Another popular method is by measuring the current emitted by a photovoltaic cell.

http://en.wikipedia.org/wiki/Radiant_flux http://en.wikipedia.org/wiki/Candlepower http://en.wikipedia.org/wiki/Lumen_(unit) http://en.wikipedia.org/wiki/Luminous_flux

Answer 2

Solar flares are classified as A, B, C, M or X according to the peak flux (in watts per square meter, W/m2) of 100 to 800 picometer (1 picometer equals 1 trillion of a meter) X-ray near Earth, as measured on the GOES (geostationary operational environment satellite) spacecraft. Each class has a peak flux ten times greater than the preceding one, with X class flares having a peak flux of order 10−4 W/m2. Within a class there is a linear scale from 1 to 9, so an X2 flare is twice as powerful as an X1 flare, and is four times more powerful than an M5 flare.

Answer 3

The Sunspot Cycle is measured from the minimum to the next minimum, which is generally about 11 years. Typically, there will be about 12-15 months of VERY low sunspot activity, at which time the Sun will become more active and more sunspots will begin to appear.

However, the cycles are not precisely 11 years, and can vary from cycle to cycle. For about the past 250 years, astronomers have been keeping track of the number and size of sunspots each day, and this is consolidated into a "Sunspot Number" each day. At the Solar Minimum, the sunspot number is usually zero or some small number. At the Solar Maximum, the Sunspot Number typically peaks above 200.

The current Solar Minimum has lasted a little longer than most, but the record (since people began keeping records) was the Maunder Minimum, a period of 70 YEARS of very low solar activity.

The Sunspot Plotter at SpaceWeather.com will let you examine any decade in the last 250 years to see what the sunspot number was doing. See the link below.