From: Richard Aiken

> I can see that. For one thing, I imagine any conceivable focusing mirror for any significant fraction
> of that amount of light would melt well below that level.

Nah, just make it bigger. The other problem is that the actual limit is 'as bright as the sun, if it covered the same fraction of the sky as the mirror does', so to even reach that limit you need an array of mirrors that covers the entire sky (or at least, the entire sky as visible from the point that is being targeted). For lesser coverage, multiply total energy by (sky coverage in steradians)/2pi.

> But I'd think you could get up a spot temp high enough to vaporize a battleship while also still well
> below that same level.
>
> (googling . . . .)
>
> The black body temp of the sun's surface is 5777 K.
> The vaporization temperature of steel is 3273.15 K.
>
> So if the sunbeam array can focus 57% of the sun's effective surface temp on one spot . . . POOF!
>
> Or am I missing something?

Luminous intensity of a 5777K blackbody = 5777K^4 * 5.67e-8W/m^2/K^4 = 58.8 MW/m^2.

Total energy to convert steel to vapor: ~7.5 MJ/kg or 58 GJ/m^3.

Effective drilling rate of maximal sun ray: 1mm/sec. Actually less due to the fact that somewhere around 60% of the light will be reflected.