A nuclear explosion is incredibly bright, as a matter of fact, it can blind your eyesight. Thus, a direct view is not possible. The US military on the other hand manage to capture one of their previous nuclear tests on video. The usual clips available for viewing are short, but this one from the military is quite long. It will give you a horizontal view of the explosion, including the details of how a huge fireball glows out of it, and how the so-called mushroom cloud forms.