Celestial News: Saturn takes center stage
June 1, 2017
Before the advent of the telescope in the 17th century, astronomers knew of five planets in our night sky: Mercury, Venus, Mars, Jupiter and Saturn. Careful observations revealed that each planet had its own unique motion through the heavens.
Mercury moves the fastest, completing an orbit of the Sun in only 88 days (0.24 years). Venus requires 225 days to orbit the Sun (0.62 years), Mars 687 days (1.9 years), Jupiter 4,333 days (11.9 years) and sluggish Saturn takes 10,759 days (29.5 years).
In my 64 Earth-years of life, Saturn has gone around the Sun twice, so I am only 2 years old, reckoned in Saturn-years. It is because of Saturn's very slow motion through the constellations that it was identified with the Greek god Cronus, who we personify today as Father Time. Mythologically, Saturn (Cronus) was the father of Jupiter (Zeus) and the grandfather of Mars (Ares).
When Galileo aimed his 30-power telescope at Saturn about 1610, he noticed peculiar bumps on either side of the planet. He described them as looking like cup handles and referred to them as the "ears" of Saturn. He speculated that the bumps might be moons, one hugging each side of the planet. After all, he had discovered four such moons when he observed the planet Jupiter with his telescope.
It wasn't until 1655 that Dutch astronomer Christiaan Huygens, using a better telescope, recognized Saturn's "ears" as being a flattened ring, completely encircling the equator of the planet. The same year, Huygens also discovered Saturn's only giant moon, Titan.
Twenty years later, Italian astronomer Giovanni Cassini first spotted the large gap in Saturn's rings that now bears his name. He also discovered the moons Tethys, Dione, Rhea and Iapetus. Thus, our fascination with the incredible ringed planet began.
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Slow-moving Saturn takes center stage in our evening sky this month as it arrives at opposition to the sun. Every 378 days, Earth gains a lap on sluggish Saturn and passes directly between Saturn and the sun, placing the two planets as close together as possible. When Saturn reaches opposition June 15, it will be 9.05 astronomical units, or 841-million miles, from Earth, its closest point for 2017. Saturn will rise in the southeastern sky as darkness falls and will shine brightly all night, from sunset to dawn. The hours around midnight will be the best for viewing Saturn, when it is highest in our southern sky.
To help you locate Saturn in the sky, the nearly full Milk Moon will rise alongside Saturn on June 9. The nearly full Thunder Moon returns for an encore performance a month later, July 6. Saturn should shine right through the moonlight, but covering that full moon with your hand will make spotting the nearby planet much easier.
This year, Saturn shines down on us from the unofficial "13th constellation of the zodiac," Ophiuchus, the Serpent Bearer. Look for it roughly a hand span at arm's length east of the Scorpion's bright-red alpha star, Antares.
A telescope of almost any size, aimed at Saturn, will reveal its beautiful icy rings and the largest of its moons, planet-sized Titan. A 6-inch or larger telescope can reveal several of Saturn's medium-sized moons, as well. Of these, Rhea, Dione, and Tethys are easiest to spot. In all, Saturn has 62 confirmed moons.
This year, Saturn's rings are tilted to their maximum possible angle of 27 degrees toward Earth, something that occurs only once every 15 years. For the next seven years, the ring angle will slowly decrease until they turn themselves edgewise to Earth and effectively disappear from view for a few months in late 2024.
NASA's Cassini spacecraft continues to beam back jaw-dropping images of Saturn, its rings and moons, but not for much longer. Cassini's incredible 20-year mission of discovery will come to an abrupt and fiery end Sept. 15, when the fuel-less explorer dives into the atmosphere of Saturn and burns up like a blazing meteor, a billion miles from home.
You can follow the adventures of Cassini on the NASA website, nasa.gov/mission_pages/cassini/main/index.html.
A view of Saturn's rings in a backyard telescope is one of the greatest "Wow!" moments astronomy has to offer, so dust off that old telescope and aim it at Saturn this month to see the solar system's crown jewel at its very best.
Jimmy Westlake recently retired from Colorado Mountain College after 19 years as professor of physical sciences and is looking forward to spending a lot more time under the starry sky. His “Celestial News” column appears in Steamboat Today the first Friday of every month. Check out Westlake’s astrophotography website at jwestlake.com.