By David Huestis, Historian, Skyscrapers, Inc.
Stunning Saturn Shares Summer Sky
Since the beginning of the year I’ve been touting the prime-time return of Jupiter, Saturn and Mars. Last month I provided an observer’s guide to Jupiter. Bright Jupiter continues to be easily observable during July, starting out the month about 35 degrees above the southern horizon. You’ll still have a couple of months to explore Jupiter’s striped bands and zones, the Great Red Spot, and the procession of his Galilean moons.
However, perhaps everyone’s favorite planet will soon steal the spotlight from its neighbor. I’m talking about Saturn and his exquisite system of rings. When word gets out that Saturn will be among the visual treats offered by telescopes at the local observatories, one can expect long lines of stargazers wishing to observe this beautiful planetary system. As astronomer Garrett P. Serviss wrote in his 1901 book, Pleasures of the Telescope, “When Saturn is in view the owner of a telescope may become a recruiting officer for astronomy by simply inviting his friends to gaze at the wonderful planet. One returns to it again and again with unflagging interest, and the beauty of the spectacle quite matches its singularity.”
Amateur astronomers and casual stargazers who are fortunate to own telescopes have been following Saturn for months. They were able to observe this beautiful ringed-world during pre-midnight hours. Their desire to explore the heavens was not hindered by the early closings of the public night observing sessions held during late winter into early spring.
However, good things come to those who wait. On June 27 Saturn was at opposition (opposite the Sun in the sky). When the Sun set that evening Saturn rose. That event also signaled Saturn’s closest approach to the Earth for 2018 (841,140,152 miles.) Therefore your exploration of Saturn can begin immediately and a telescope will reveal a slightly larger image of the planet than your sleep deprived associates experienced.
Saturn can be found in the constellation of Sagittarius, just above the “teapot” asterism and nestled among the stars of the gauzy (depending upon the amount of light pollution from your observing location) Milky Way. By 10:00 p.m. on July 1, Saturn will be about 20 degrees above the southeast horizon and will be the brightest object in this region of the sky. It will be tempting to begin observing Saturn as soon as you can locate it. However, you may wish to wait another hour or so for Saturn to climb higher into the sky to minimize the effects of atmospheric turbulence on image detail.
Each night Saturn will rise higher into the sky as it moves towards the west. By the 20th of the month it will be only about 25 degrees above the southern horizon at 11:00 p.m. This minimal degree in altitude change is because the ecliptic (path of the Sun through our sky and therefore the plane of the solar system) traverses a low arc across our summertime night sky. This scenario is true for Jupiter and Mars this summer as well, as the planets also trace out the ecliptic. Much better views will be obtainable from more southerly latitudes.
When you first observe Saturn through a telescope its rings will initially take your breath away. They are really an impressive sight to behold. The rings are composed of irregularly shaped dirty snowballs, ranging in size from grains of dust to the size of pebbles. There are also some “boulders” as large as several feet across. They all orbit Saturn along the planet’s equatorial plane. It is really amazing that Saturn’s rings are even visible at all, considering the planet’s great distance from the Earth and the fact that the main rings are only about 32 feet thick, whereas other portions of the ring system can be up to about two-thirds of a mile thick.
Furthermore, the ring system is currently tilted 26 degrees toward the Earth providing us with a view of the north face of the ring plane. With the rings so “wide open,” this configuration allows much detail to be seen. Look for gaps within the ring system. You shouldn’t have any difficulty seeing the separation between the primary “A” (outer) and “B” (inner) rings, called the Cassini Division. This gap is only 2,175 miles wide. In comparison, the width of the “A” ring is 9,321 miles and the “B” ring is around 16,032 miles across. Saturn’s rings are slowly de-orbiting and will eventually all “rain” down onto his cloud tops in 50 to 100 million years or so and cease to exist. So you’ve got plenty of time to enjoy the view.
Though Saturn is a gas giant a little smaller than Jupiter, it does not exhibit the prominent bands and zones in its cloud tops as its larger cousin does. Not much detail can be observed at all on Saturn’s disk. In fact, if it weren’t for Saturn’s ring system, this planet would be quite a boring destination for most amateur astronomers and the public alike.
In addition, both before and after opposition as our viewing angle changes, a keen-eyed observer can look for the shadow of the rings upon Saturn’s cloud tops as well as the shadow of Saturn onto his rings. Also, with the rings so wide open they currently block our view of the Saturn’s south polar region.
And finally, Saturn is accompanied by 62 confirmed moons. One can detect up to eight of its brightest moons in a dark moonless sky under ideal seeing conditions with the telescopes available locally and follow their orbital motions around Saturn. In order of size and brightness they are Titan, Rhea, Iapetus, Dione, Tethys, Enceladus, Mimas and Hyperion
While a small two-inch telescope will reveal the beauty of Saturn, search out larger instruments available throughout Rhode Island to explore this exquisite ringed world in splendid detail. Seagrave Memorial Observatory in North Scituate (http://www.theskyscrapers.org) is open every clear Saturday night for observing. Ladd Observatory (http://www.brown.edu/Departments/Physics/Ladd/) in Providence is scheduled to reopen Tuesday, July 10, and every clear Tuesday thereafter. The Margaret M. Jacoby Observatory at the CCRI Knight Campus in Warwick (http://www.ccri.edu/physics/observatory.htm) is open every clear Thursday night. Also consider visiting Frosty Drew Observatory (http://www.frostydrew.org/) in Charlestown on every clear Friday night. Please visit the respective websites for details. These observing sessions are free and open to the public.
Join the volunteers at these facilities as they share their love for the beauty of our solar system. August’s column will prepare you for the Earth’s upcoming close encounter with Mars (approximately 35,800,000 miles away) on July 31. Mars won’t be closer until September 11, 2035.
As always, keep your eyes to the skies.