Once a year Saturn and Earth line up on the same side of the sun. The event is called opposition, when the two planets are the closest together. From our perspective on Earth, Saturn will be opposite the sun in the sky. If you face south this evening with the setting sun on your right, Saturn will rise directly opposite in the east at sunset and remain visible all night.
Last year’s opposition date was April 3; this year it’s April 15. Saturn oppositions occur about two weeks later each year because in the time it takes the Earth to return to another lineup, Saturn has also along traveled further along its orbit. We need about two weeks to “catch up” with the ringed planet and re-align for another opposition.
Since Saturn is the brightest and biggest it will be this year, the coming weeks are an ideal time to train your telescope on the planet for a satisfying look at its rings and satellites. At low power in a small scope you’ll see one ring and Saturn’s brightest moon Titan, the only satellite in the solar system with a significant atmosphere. Observers with larger telescopes will spy Titan’s orange-red color caused by hydrocarbon smog. I’ve easily seen the moon’s hue through my 10-inch reflector when it’s off to one side of Saturn.
Larger scopes and calm air also reveal that the single ring is split in two by a narrow dark gap called Cassin’s Division. And if you’re patient, you’ll also see a third, semi-transparent inner ring called Ring C or the Crepe Ring. A thick, gray band – the North Equatorial Belt – crosses the planet between the ring plane and its north pole.
As for Saturn’s family of moons, I mentioned that Titan was visible in a small scope. The moon Iapetus (eye-AP-it-tuss) is almost as easy to spot when it’s far to the west of the planet (western elongation) and showing off its icy hemisphere.
When the moon swings east of Saturn, we see its much less reflective darker hemisphere, causing the moon to dim by nearly two magnitudes from 10.2 to 11.9. As fortune would have it, Iapetus is at western elongation and bright right now. The smaller, fainter moons Dione (dye-OH-nee), Rhea (REE-uh), Tethys (TEE-thiss) and Enceladus (En-SELL-uh-duss) are also visible in larger scopes.
The Mars event is far less dramatic than Saturn’s opposition. For some months now, the Red Planet has been moving west in retrograde motion, closing in on Leo’s brightest star Regulus. Today it stands still – briefly – and then resumes its normal eastward motion.
Astronomers say that Mars reaches its “stationary” point before resuming “direct” motion. What it means for us is that the planet will now slowly depart from its bright companion Regulus.
Mars, like all the planets outside Earth’s orbit, appears to travel backwards for a time as the faster-orbiting Earth catches up and passes the planet around the time of opposition. It’s similar to passing a car on the freeway. As you approach the car you plan to pass, it appears to slow down and go “backwards” as you drive by and watch it disappear in your rear view mirror.
Since planets orbit in ellipses and not straightaways like freeways, they soon resume their normal motion a month or so after Earth passes them.
Keep an eye on Mars over the next month and you’ll see it pick up speed as it cruises through Leo and into Virgo where it meets Saturn for a nice conjunction in mid-August.
Just in case you’re still now familiar with where to look for Mars and Saturn, use the map below, which is drawn for 9:30 p.m. local time. Wishing you all clear skies and great Saturn viewing!