Just How Big Was the Death Star? And How Powerful is the Laser Onboard?

So over this past couple days I watched the original Star Wars trilogy and it got me thinking: just how big is the Death Star? Well....let's try to find out!

I found a scaled print of the Moon of Endor and the Death Star II

The Moon of Endor according to Wookipedia is 4,900 km in diameter.  The size of the planet in the picture is around 7.4 cm putting that into km it is .000074 km in diameter.  In proportion to the reported size of the planet, which is 4,900 km, dividing the two together would give you the scaling.  The answer I came up with is 1/66216216.2 km scale (approximately).  If the Death Star II was only .6 cm in this picture it means that it would be .000006 kilometers in diameter.  Multiply that by 66216216.2 and you have our diameter of just around 397 km in diameter.  

The accomplishment of the complete disruption of an Earth-like planet sets a lower limit to the destructive capability of the Death Stars' prime weapon. The gravitational binding energy of a planetary body is the minimum amount of energy required to eject all of its material with sufficient force that it will not fall back together. (It is also the total energy which would be released as heat if the entire substance of the planet were gathered together from free space.) For an object of a given mass the gravitational binding energy is increased when a greater fraction of the mass is concentrated near the centre. The density of a planet tends to increase with depth from the surface, because the weight of overlying material causes pressure to increase with depth, and heavier materials tend to sink towards the core when a planet forms.

Alderaan is probably a typical habitable planet, with much the same dimensions and composition as our Earth. An approximation for its gravitational binding energy can be obtained according to the density structure profiles of the Earth or Venus. An approximate figure for the binding energy of Alderaan, assuming Earthlike composition and mass of 5.9 x 10²⁴ kg, is:


U = 2.4 x 10³² joules.

This is just the minimum amount of energy required to destroy the planet, the Death Star could, in fact, have a much, much greater than what I have collected.