Saturn puts in its best appearance of the year over the next few nights. On Sunday, it’ll reach opposition – it will line up opposite the Sun. It’s closest to Earth at opposition, so it shines brightest. And it’s in view all night. It looks like a bright golden star. It’s low in the east at nightfall, and climbs high across the south later on.
Saturn reaches opposition every 12 and a half months – the result of the combined motions of Saturn and Earth. Earth orbits the Sun at an average speed of about 67,000 miles per hour. Saturn is more than nine times farther from the Sun. And thanks to the laws of orbital motion, it moves only a third as fast as Earth.
Johannes Kepler formulated those laws four centuries ago. He determined that the planets follow elliptical orbits; instead of perfect circles, the orbits are stretched out. There’s a relationship between the planet’s distance and its orbital period – the time it takes to make one full turn around the Sun. And a planet moves fastest when it’s closest to the Sun, and slowest when it’s farthest.
Earth’s distance varies by only about three percent, so there’s not much change in its orbital speed. But Saturn’s distance varies by more than 10 percent, so there’s a bigger change in its speed.
All of this works together to bring Saturn into alignment every 12 and a half months – shining at its best.
More about Saturn tomorrow.
Script by Damond Benningfield