What is the significance of one-third in Revelation?

Why is everything 1/3 in Revelation? It comes up with the four angels, and the dragon: > 8:7 The first [angel's trumpet] sounded, ... and a third of the earth was burned up, and a third of the trees were burned up, and all the green grass was burned up. 8 The second angel sounded, ... and a third of the sea became blood, 9 and a third of the creatures which were in the sea and had life, died; and a third of the ships were destroyed. 10 The third angel sounded, and a great star fell from heaven, burning like a torch, and it fell on a third of the rivers and on the springs of waters. 11 The name of the star is called Wormwood; and a third of the waters became wormwood, and many men died from the waters, because they were made bitter. 12 The fourth angel sounded, and a third of the sun and a third of the moon and a third of the stars were struck, so that a third of them would be darkened and the day would not shine for a third of it, and the night in the same way. > > 9:15 And the four angels, who had been prepared for the hour and day and month and year, were released, so that they would kill a third of mankind. 18 A third of mankind was killed by these three plagues, by the fire and the smoke and the brimstone which proceeded out of their mouths. > > 12:4 And [the dragon's] tail swept away a third of the stars of heaven and threw them to the earth.