Tonight – May 22, 2015 – the ringed planet Saturn reaches opposition, a big milestone for our year of observing the ringed planet! Earth passes in between Saturn and the sun on May 23 at 0200 Universal Time. For the Americas, that places Saturn’s opposition on May 22 in the evening (9 p.m. CDT).
So this is Saturn’s special day, its yearly opposition, when it is opposite the sun as seen from Earth. In other words, Saturn is opposite the sun in Earth’s sky. As a consequence, Saturn rises in the east at sunset, climbs highest up for the night at midnight and sets in the west at sunrise. It is visible all night, closest and brightest for this year.
Just don’t assume this is a one-night-only event. In fact, Saturn’s opposition guarantees the ringed planet will be in good view throughout May and June 2015. Moreover, Saturn will remain a fixture of the evening sky until September or October 2015. All the while, golden Saturn shines in close vicinity of ruddy Antares, the brightest star in the constellation Scorpius the Scorpion.
Want to recognize Saturn? Here are two hints:
1. It’s near Antares, which is a reddish, very bright and a great twinkler.
2. It’s near an arc of three stars close to Antares in the night sky, called the Crown of the Scorpion.
What is opposition? Our fast movement in orbit brings Earth between Saturn and the sun every year – or, more precisely, about two weeks later every year. Last year, for instance, Saturn’s opposition happened on May 10, 2014. This year, opposition happens on May 22-23, 2015. Next year, in 2016, Saturn’s opposition will come on June 3. If you recognize this golden world tonight or later this month, you’ll also enjoy it throughout the Northern Hemisphere summer, or Southern Hemisphere winter.
If you had a bird’s-eye view of the solar system today, you’d see our planet Earth passing in between the sun and Saturn. You’d see the sun, Earth, and Saturn lining up in space. But not for long. Earth moves in orbit at 18 miles per second in contrast to about 6 miles per second for Saturn. Soon, we’ll be pulling ahead of Saturn in the race of the planets.
The inner planets – Mercury and Venus – can never be at opposition, because they orbit the sun inside Earth’s orbit. Only the planets that orbit the sun beyond Earth’s orbit – Mars, Jupiter, Saturn, Uranus and Neptune – can ever reach opposition, that is, appear opposite the sun in Earth’s sky.
All the planets farther from the sun reach opposition every time our swifter-moving planet sweeps between the sun and them. That happens about once a year, since Earth takes a year to orbit the sun once, and since these outer worlds move more slowly than we do.
Saturn, the 6th planet outward from the sun, is the most distant world that’s easily visible to the unaided eye. Telescopes revealed its rings in the 17th century. Spacecraft in the 20th century revealed that what we thought of as three rings around Saturn to be thousands of thin, finely detailed rings – made of tiny chunks of ice. Saturn also has 62 moons with confirmed orbits. Only 53 of Saturn’s moons have names, and only 13 have diameters larger than 50 kilometers (about 30 miles).
Saturn is truly a wondrous world of rings and moons. It’s everyone’s favorite thing to see through a small telescope, so if there’s a public astronomy night near you this month – go!
Bottom line: Look for Saturn at opposition tonight – May 22-23, 2015. It will be shining in the east this evening, above the bright star Antares. Can’t see Saturn tonight? No problem. It’ll be in an excellent place to observe throughout May and June 2015.