As a result of recent events, one hears a great deal about solar flares - their attributes, and so forth. However, solar flares have one (I would surmise) fairly important feature, about which the internet appears to be struck dumb. It's this: assuming such flares expand ever further outwards - possibly conically? - once they leave the Sun's surface, just how spatially 'wide' are they by the time they reach Earth orbit? I guess this might vary, depending on the initial energy release etc. All I'm after is an average ballpark figure, if such a thing exists. Many thanks.

 

PS. Happy Solstice Day!

There's note that the terminology is wrong in the video, it's actually a prominence and not a flare, but the answer to that one is "of order 10 earths". (He also talks too fast, IMO). So that doesn't really answer the question other than give a rough order-of-magnitude expectation.

 

http://www.universetoday.com/88013/how-big-are-solar-flares/

 

The size is measured on the sun in order to classify them

http://www.ips.gov.au/Educational/2/4/2

 

Unfortunately, as you note, the typical internet discussion on effects at the distance of the earth is on damage and energy of the flare, not its physical size.

Many thanks. According to the video, it seems that a typical solar flare extends out to about 'several dozen Earth diameters' by the time it crosses Earth orbit. This surprises me. I had always assumed these flares, and/or CME events, were messy, inherently chaotic and widely distributed affairs - like any unrestricted explosion, in fact. I hadn't expected them to be so pencil thin. It appears then that a spread of (say) just 400,000 km over a distance of 1 AU does make for an extremely narrow, almost laser-like beam. I don't pretend to understand the physics involved, but it might help to explain why any such impacts by these 'solar superstorms' (like the one that almost struck the Earth in 2012) are so fleetingly rare, after all.

Several dozen earths is fairly small by solar standards, big by earth standards. The weakest classification by area is ~1/4 earth size on the sun's surface, which I'm guessing is earth-sized by the time it reaches us.