Balance in the Solar System

Science is behind these mysteries

The waning crescent moon rises before dawn at week’s end. In the hour before dawn Friday morning, the razor-thin crescent is within 10 degrees of brilliant Venus and more subdued Saturn. Mercury shines surprisingly bright below the moon, although you may need binoculars to pick it out against the glowing horizon.

While Saturn is more than 10 times the size of Venus — larger, in fact, than all the planets combined except for Jupiter — Venus is the brightest object in the heavens other than the sun and moon. Why? Remember that planets, even gaseous giants like Saturn and Jupiter, don’t emit their own light. Instead we are seeing sunlight reflected from their surfaces and back to us here on Earth. That light has to travel 10 times farther just to reach Saturn as opposed to Venus, and it then has to travel back 10 times farther to reach our eyes.

It would be a different story if Saturn were in place of Venus, in which case the ringed planet would appear like another moon in our sky. However, it isn’t mere coincidence that the inner planets are small and solid while the gaseous giants dwell in the outskirts of the solar system. It’s all a matter of balance. Were these giants closer to the sun, our solar system’s real monster, their own mass would work against them in a gravitational tug of war, and they would be torn asunder.