Saturn opposition season never disappoints. Slowly, one by one, the planets are returning to the dusk sky. In June, we had Jupiter reach opposition on June 10th. Now, although Mercury and Mars are fleeing the evening scene low to the west at dusk and Venus lingers low in the dawn, magnificent Saturn reaches opposition tonight on July 9th, rising to the east as the Sun sets to the west.
Opposition Season 2019
Saturn opposition is always the star of any viewing party. On our last public viewing expedition out with the Back Bay Amateur Astronomers just south of Norfolk on the edge of the Great Dismal Swamp, we extended the session just long enough to show off Saturn as it cleared the treetops.
In 2019, the path of Saturn takes it on a looping trek through the southern constellation of Sagittarius the Archer towards the constellation of Capricorn the Goat. Along with the 2018 opposition, this is one of the southernmost oppositions for Saturn for the next few decades. This also means that in 2019, Saturn opposition will ride high across the zenith for southern hemisphere observers near midnight, but sit ‘in the weeds’ due south for observers up north. Saturn won’t peek north of the celestial equator until 2026.
Saturn isn’t just crossing the star-dappled region near the core of the Milky Way galaxy, however. It also serves as a good beacon towards a few other notable celestial locales in 2019. Look on the opposite side of the Teapot asterism towards the spout, and you’re looking in the direction of the supermassive black hole at the core of our galaxy known as Sagittarius A* (“A-star”) enshrouded in a cloak of gas and dust. Saturn is also very near a patch of sky around the star Tau Sagitarii where, in 1977, radio astronomers at Ohio State University picked up the infamous Wow! Signal.
Saturn is also in the midst of a series of fine lunar occultations in 2019, running out until December 2019. Saturn is a slow-moving target for the swift Moon, taking 29.5 years to circle the Sun and the zodiac. Saturn oppositions only shift an average of 13 extra days from one year to the next, the most leisurely of the naked eye planets. In 2019, we’re seeing Saturn cover the same patch of sky it visited waaaaay back in 1989.
To the naked eye, Saturn presents an unassuming, +0.05 magnitude dot. This represented the very edge of the solar system, right up until Sir William Herschel discovered the planet Uranus on the night of March 13th, 1781.
One naked eye phenomenon to watch for around opposition is what’s known as ‘opposition surge,’ or the Seeliger effect. This is a boost in brightness, brought on by a retro-reflector style effect, similar to having your car high beams bounced back at you off a highway sign at night. This effect is especially prominent on Saturn, when its rings are at maximum tilt with respect to our line of sight.
At the eyepiece, Saturn presents a 18” disk in July, with rings expanding that distance to 43” from tip-to-tip. The glorious rings of Saturn are tipped 25 degrees wide in 2019, narrowing from a maximum of 27 degrees in 2017 and heading towards edge-on in 2025. Crank up the magnification, and the dark groove of the Cassini gap in the rings becomes readily apparent.
Keep an eye out for the moons of Saturn as well. +8.5 magnitude Titan is an easy catch with binoculars, while small telescope users can check Enceladus, Rhea, Iapetus, Mimas, Dione and Tethys off of their life list. Dedicated large light bucket owners might just be able to spy difficult Phoebe and Hyperion, as well.
Watch Iapetus, as it varies in magnitude from +10 to +12 during one 79 day orbit, due to two hemispheres of differing brightness. Situated well out of the ring plane, Iapetus would make an ideal Saturn viewing location:
The most recent round of exploration at Saturn ended in 2017, when NASA’s Cassini plunged into the planet. In 2034, NASA plans to follow up with a recently announced nuclear-powered helicopter mission, headed to Titan. A possible dedicated Enceladus mission is also on many astronomers’ short list.
Be sure to check out Saturn this summer. Hopefully, we’ll be back there soon.