By the way, by the OP the Death Star
appeared in the sky close enough that it was able to be seen with people's eyes. Assuming it's at the highest point still considered "atmosphere", then the Death Star
is up in the exosphere
The Death Star
was six planetary diameters away from Alderaan when it destroyed it, equal to about 76,000 km. The beam, according to the quote I posted on the previous page, took 10 seconds to travel from the superlaser dish to the planet*. So the beam has a speed of about 7,600 km per second. At that speed, and assuming the Death Star
is 10,000 km up in the "sky", it'll take the beam 1.31 seconds to hit the Earth. Add in the "second or so for the tributary beams to coalesce"
, Vegeta has either 2.31 to 3.31 seconds to finish charging up, to move into position, to fire whatever attack he's shooting and for the attack to reach out and deflect/overwhelm/destroy the superlaser before it blows up the Earth.
If the Death Star
is at the beginning of the exosphere, at around 500 km in the sky, then Vegeta has only 1 or 2 seconds to do all those things. Since at the superlaser's speed it'll be an almost instant hit after the beams form the main superlaser shot.
Then ask yourself when, in the entire history of Dragon Ball
, has someone charging up ever taken less than a second or two.
*This is going by the timer and assuming it counts the exact moment of destruction, going by the movie the beam travels from the Death Star
to Alderaan in about a second.