Energy Levels Around Stars

[Simon_Jester]

I've been thinking about science-fiction settings where spacecraft are operating very close to stars for one reason or another. Over the years, I know that a number of people have brought up things like "operating in a stellar corona for X hours" or "survived being hit by a solar flare" in versus debates. I've seen some of the references to them, but they are scattered widely.

So what I'd like to do is ask: does anyone remember figures for these things? What kind of intensity (watts per meter squared) would you expect from things like just being in the corona, or being inside a solar prominence? Who remembers where they come from?

[HMS Conqueror]

Solar luminosity is 3.846×10^26 W. The irradiance is just that divided by the area.

So Irradiance = 3.846x10^26/(4*Pi*R^2).

R includes the radius of the sun itself, which is 700,000,000m. The corona is somewhat nebulously defined. At 1,000,000km, the irradiance would be 31MWm^-2. At 2,000,000km, the irradiance would be 7.7MWm^-2.

At the radius of the earth, 150,000,000km, the irradiance would be 1,360Wm^-2, which is in close agreement with measurements.

[Simon_Jester]

Well, I'm also interested in seeing if anyone's done or seen a more sophisticated analysis- say, the energy you'd expect to get dumped on you from bathing in the plasma of the corona, or (as noted) inside a prominence or flare.

[HMS Conqueror]

It won't be significant in the first case. The plasma is at a famously high temperature but it is extremely rarefied, so the heat flux is much less.

[Simon_Jester]

I wasn't really expecting much from the white-hot vacuum of a stellar corona, but I was wondering if anyone has figures for the latter cases.