The proceeding episode of Dragon Ball Z is the most metal episode so far reviewed of the franchise here on Dragon Blog (Z). As such, I highly recommend that while you look over this blog entry, you listen to this song.
Vegeta can scarcely fathom it. Kakarotto, low class trash, the scum of the Saiyan race, is not only matching he, the proud Prince Vegeta, in strength... he's completely throttling him in every possible way. But unknown to Vegeta, the Kaio-ken x3 is beginning to take its toll on Son Goku's body. Both fighters wish to see this fight end quickly, as both feel they're on the ropes.
Burning with rage, Vegeta makes to end the battle by destroying the entire planet... with his most powerful attack, the Gallic Ho!!
Goku has one option...!! The Kaio-ken x3...
"Ka... me... ha... me..."
"I'm going to turn you and this planet into space dust!!"
Yajirobe (who has been watching the entire fight from the sidelines, natch) congratulates Goku on a job well done. But Goku isn't so sure his job is done... If Vegeta was that easy to finish, their fight wouldn't have lasted so long, he reckons. ("Easy"? You launched him into fucking space with two beams containing enough destructive force to end several planets.)
Sure enough, Vegeta's alive, and he's not happy. Though it pains him to do it, Vegeta will use the final trick up his space gloves; Oozaru. Kaio-sama chuckles as Vegeta struggles to find the Earth's moon, knowing full well that Piccolo destroyed it, thinking this would happen (and how does Kaio know this exactly? He hadn't met Goku yet. Y'know what? Lets not think about it). Vegeta is undeterred, however. Although he'll sacrifice some of his ki, Vegeta has an alternate method for making the transformation work.
Vegeta lands and explains to Goku how the Oozaru transformation works. When Bruits Waves reflect off the full moon's surface, enough of these mysterious waves enter their eyes and set off a reaction in their tails. This causes their transformation.
And Goku makes this face.
(As does the viewer.)
Seeing that Goku isn't paying attention, Vegeta tells him that Goku's father was an average fighter, but a brilliant scientist. And that he invented artificial full moons when facing down radical weaponry on Rygal 7.)
Vegeta creates an artificial source of moon light, to be mixed with Earth's oxygen.
And thus, Vegeta creates a brand new full moon.