[BurningFrog]

Is the main radiation danger the Sun or the background "cosmic" radiation?

I've been assuming the latter, but I realize now that I don't actually know.

[marze]

Both are significant dangers, but radiation from the sun can be shielded fairly easily. Not so high energy cosmic rays.

[BurningFrog]

You can for example put an entire planet between you and the sun radiation by going out at night.

[eru]

Doesn't matter too much for the rocks: if a few metre of rock won't absorb the radiation, neither will your body.

[schoen]

That doesn't make too much sense to me, since your body could be harmed by absorbing only a fraction of the energy of a large radiation dose.

[eru]

Valid point. Though I think given the spectra involved, it probably doesn't apply.