Upon seeing the sky light up from a nuclear detonation, what is your immediate action?

The appropriate immediate action upon witnessing a nuclear detonation, particularly when dealing with the initial blinding flash, is to protect your eyes. The intense light produced can cause severe temporary or permanent eye damage, such as flash blindness or retinal burns. Closing your eyes helps to shield them from this potentially harmful burst.

In addition to protecting your vision, it is important to seek cover to protect yourself from the shockwave and subsequent fallout. While closing your eyes is critical for eye safety, the ideal course of action in a broader context would include finding shelter as soon as possible to mitigate the effects of radiation and the shockwave that follows the initial blast. Options that suggest dropping to the deck or flexing your knees may offer some protection during an explosion but do not specifically address eye safety, which is a unique aspect of a nuclear detonation scenario. Grabbing a solid structure can provide cover from debris or the shockwave but overlooks the immediate need to protect one’s eyesight from the blinding flash.