Starwatch: Saturn joins the summer planet parade

July 7, 2018 GMT

There’s planet congestion this month as Saturn joins Venus, Mercury, and Jupiter in the early evening heavens, and in my book it’s the best planetary telescope target.

I’m certainly not alone in that opinion. I hear oohs and awws and many other reactions during my star parties when my arsenal of telescopes are turned toward Saturn.

Even if you have a small telescope, you can enjoy the majesty of the ringed wonder of our solar system. Many lifelong amateur astronomers can point back to their first look at Saturn through a department store telescope as their launching pad into this great hobby!

Not only is Saturn back in our evening skies and available until morning twilight, but it’s also as close to Earth as it’ll be in 2018. On June 27, Saturn and Earth, in their respective orbits around the sun, reached what astronomers call opposition.

As you can see in the diagram, that’s when the Earth lies in a line between the sun and Saturn. Not only does that make Saturn available all night, but puts Saturn at a minimum distance to Earth. This happens with Saturn and the Earth every 378 days.

Toward the end of evening twilight, look in the low southeastern sky for the brightest starlight object you can see in that immediate area and that’ll be Saturn. A little higher up in the south-southwestern sky is Jupiter. It’s the only thing that outshines Saturn in the southern half of the early evening sky.

Even though Saturn and Earth are at their closest approach to each other for 2018, they’re really far apart. The second-largest planet in our solar system is still better than 830 million miles away. A jet airliner flying at top cruising speed would take more than 170 years to get there!

Earth is still my favorite planet in our solar system, but the dynamic ring system makes Saturn a close second. It’s 75,000 miles in diameter, nearly 10 times that of the Earth.

While Saturn’s ring system is so vast in width, it’s only at the most about 50 feet thick! The best bet theory for origin of Saturn’s rings is that they were created about a 100 million years ago, when a passing moon or water-laced comet got a little too close to Saturn and was merely blown to bits of debris and ice, shredded by the massive planet’s tidal forces. All of these bits range in size from dust particles to school bus size, spread out in their own individual orbits in nearly the same plane around Saturn.

The ring system is so bright because of all the ice. In fact, most of Saturn’s brightness as seen from Earth is due to sunlight bouncing off the ring system even though Saturn is as far away as it is.

Saturn, just like its larger neighbor, Jupiter, has many moons, and some of these moons act as gravitational “shepherd” moons that help keep Saturn’s ring system intact. Titan is Saturn’s largest moon, and in fact it’s even larger than the planet Mercury, closest planet to the Sun.

Titan has a heavy methane atmosphere and even has methane lakes. The Cassini spacecraft that orbited Saturn for years has collected all kinds of data and images, and has even photographed sunlight reflecting on one of the giant methane lakes. In 2005, a probe launched from Cassini even landed on Titan.

As fascinating as Titan is, a small moon, Enceladus, has really grabbed some astronomical headlines as Cassini photographed water plumes gushing from cracks in the moon’s surface. It’s believed that tidal forces from the much more massive Saturn are strong enough to heat up Enceladus’s interior enough for liquid water.

Wherever there’s liquid water there’s always at least a small chance of some kind of life. Stay tuned — there’s bound to be more about this possibility in years to come.

Just as it is with the ring system, just about any telescope will show you at least some of Saturn’s moons, which resemble tiny little stars swarming Saturn with Titan decidedly brighter than the rest. They change their positions from night to night as they obediently orbit the great planet.

When you do get your telescope out for viewing Saturn, it’s best to wait until after 11 p.m. or so, so Saturn can rise high enough so you don’t have to view though as much of Earth’s blurring atmosphere. Also, make sure you put your telescope out, along with all the eyepieces, for at least a half hour before you start viewing so the optics can adapt to outside temperatures.

One more thing: When you view Saturn through your scope or any other celestial object, try to look continually at it through the eyepiece for 10 to 15 minutes. The longer you look, the more detail you’ll see.

As good as Saturn’s going to be for the rest of this summer and into early autumn, there’s yet another planet joining the summer planet parade. Mars will grab stargazing headlines as it storms onto the early evening celestial stage later this month. It will be as bright and close to Earth as it’s been in 15 years!

I’ll have much more on the 2018 Martian invasion in the coming weeks. Meanwhile, if you’re a real night owl, it’s high enough for good viewing well after midnight.