# How far was the death star from Alderaan when it blew the planet up?

Here the planet looks about the size the earth does from the moon, and since Alderaan is about the same size as the earth, I would guess, about the distance the earth is from the moon, maybe a little farther. It does appear to have moved farther away from the destruction by the time the Millenium Falcon arrives, as the Falcon probably came out of hyperspace only a few hundred thousand kilometers away from where the planet was, maybe even closer and the distance from the debris to the Death Star seems considerably longer. I was wondering, though, is the distance canonically established, and did the Death Star purposefully move away to avoid getting hit by debris from the planet?

• Seven. It was seven far. – Wad Cheber Oct 12 '16 at 3:00

They were very close indeed. Assuming Alderaan is roughly the size of the Earth, they were only about 50,000 miles away, less than 20% the distance of the Earth to the Moon.

A voice announced over a hidden speaker that they had approached within antigrav range of Alderaan — approximately six planetary diameters. That was enough to accomplish what all of Vader’s infernal devices had failed to.

Star Wars Episode IV: A New Hope (novel)

And yes, I'm fully aware that that's dumb. Don't yell at me.

• Here I was, getting ready to watch that scene, count the seconds from firing to explosion, and try and extrapolate it. Then you show up, use an actual quote to get the right answer. Show off. – CBredlow Oct 11 '16 at 22:30
• For the record, there's no indication that the Death Star moved an inch after firing its primary weapon. – Valorum Oct 11 '16 at 22:30
• @CBredlow - What's most interesting is that the destruction of Alderaan doesn't appear in the official novelisation. They show up, they threaten Leia, she gets dragged off to a "viewing gallery" and then we cut to the aftermath. – Valorum Oct 11 '16 at 22:31
• @Valorum It's quite easy to work out that the gravitational binding energy of a planet is 3GM^2/5R. Assuming that Alderaan is very much like Earth, the minimum energy required to annihilate it is of the order of magnitude 10^32J. Assuming the death star was using a very powerful laser, we can apply E = pc to conclude the momentum transfer was on the order of 10^24 Ns. If the death star was of Earth's mass, the final recoil velocity would be on the order of 1m/s. If, OTOH, it was around lunar mass, it would be around 100m/s (=360km/h). I don't know if there's canon for the death star's mass. – Deepak Oct 12 '16 at 3:41
• @Valorum I think I remember (many years back) doing some more intricate calculations on the back of a napkin with regard to probable estimates of the death star's mass based on Earth like gravity and its apparent size relative to Alderaan (assuming Alderaan was very Earth like). But I can't remember what I concluded, haha. – Deepak Oct 12 '16 at 3:42