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HomeEducationalThe Sun and Solar ActivityGeneral InfoMeaning of X-Ray Fluxes From the Sun Sunday, Dec 21 2014 13:29 UT
The Sun and Solar Activity

Meaning of X-Ray Fluxes From the Sun

The solar X-ray flux arises from two factors. Firstly, there is flux coming from sunspot regions and other features - the background flux - and this varies slowly from day to day. Secondly, solar flares produce large amounts of X-ray flux, but this is concentrated to the duration of the flare which is usually from minutes to several hours.

Solar X-ray flux is described as follows:

Level Flux (watts/sq meter) Description
Aless than 10-8Very Low Background
Abetween 10-8 and 10-7Low Background
Bbetween 10-7 and 10-6Moderate Background
Cbetween 10-6 and 10-5High Background/Low Flare
Mbetween 10-5 and 10-4Moderate Flare
Xbetween 10-4 and 10-3High Flare
Ygreater than 10-3Extreme Flare

Within these levels, a number is used to specify the flux. Hence a value M3.2 indicates that the flux is 3.2 × 10 -5 watts/metre2.

The Y classification of flares is new; and these extremely large flares are often still classed as X flares with a qualifying number greater than 10. Hence a Y1.6 flare is exactly the same as an X16 one.

Material prepared by Richard Thompson

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