A Planet Becomes a World

For overwhelmingly most of the time we have been looking at the planets, they were nothing more than colorful points of light. That changed when Galileo began his miniature mass production of the telescope. Italy was a central location in the Renaissance, and Galileo brought some serious Renaissance game.

If you ever get to Florence, yes, you should definitely go to the Uffizi, and yes, you should definitely see Michelangelo’s David, and yes, you should definitely have some food and wine overlooking the Arno. But there’s one other thing you should definitely do: visit the Museo Galileo. There you can find Galileo’s writings and illustrations from observing the planets and the Moon. These were the first detailed recorded looks at these objects, and particularly with the planets, they began to transform these colorful points of light into worlds – real places that we might one day visit.

Galileo’s telescopes were nowhere near as powerful as those you can find for even a few hundred dollars today. In fact, a good set of binoculars today will show you the same things Galileo could see. With binoculars, you can see Jupiter’s moons lined up in orbit, incredible detail in the craters of the Moon, and at least a hint of Saturn’s rings. With Mars, you can see a blurry red disk.

Binoculars and telescopes are both just buckets for collecting light. The bigger the bucket, the more light you can collect, and the more you can see. For a telescope, that means a bigger aperture (the diameter of the end that you point at the sky). The more light you can collect, the brighter the object you are looking at will appear. You can also make that object look bigger by increasing the magnification, but that will spread the light out more and make the object look dimmer. So if you look at Mars even today with the typical consumer telescope, you might see a hint of its polar ice caps and maybe a dark patch or two, but you won’t see much more detail than that. To get a clear picture with detail, you really need a big aperture. That way you’re collecting plenty of light to offset the penalty of magnification.

Once Galileo opened the door, a number of folks built on both the technology of the telescope and the observations it enables. Few if any were better at this than Christiaan Huygens. His most well-known invention was the pendulum clock, but he was brilliant in optics and astronomy as well. Huygens discovered Saturn’s largest moon – Titan – and he also revolutionized our understanding of its rings, which he showed to be thin and flat, and nowhere touching the planet itself. Consequently, when the Cassini space probe visited Saturn in 2004, it was the Huygens lander that parachuted onto Titan the following year.

With his advanced telescope and eyepiece, Huygens was the first person to see a feature on another planet – a volcanic plain on Mars now known as Syrtis Major. He subsequently observed Syrtis Major over the course of several days, and in so doing was able to estimate the length of a Martian day – coming up with 24 and a half hours. Today we know a Martian day lasts 24 hours and 37 minutes. Not bad work for someone in the year 1659. It turns out the namesake of the Cassini probe wasn’t a bad astronomer either. Among many other contributions, Giovanni Domenico Cassini noted the southern polar ice cap on Mars in 1666, and refined the length of the Martian day to 24 hours and 40 minutes. Huygens viewed the other ice cap in 1672. Over the course of the next century, astronomers made more and more observations of the polar caps, and even saw some Martian dust storms along the way.

In the 1800’s, telescope design made major advances, with apertures growing past seven inches in diameter – which is comparable to what you can get for a few hundred bucks today. Astronomer Johann Heinrich Madler generated the first map of Mars in 1840. By 1877, a 26-inch aperture telescope was possible, and Asaph Hall used one to discover Mars’ two moons – Phobos and Deimos. Not everyone had access to telescopes that large, and smaller apertures fueled some active imaginations. Also in 1877, Giovanni Schiaparelli wrote down features called canali, which he saw with an 8.7-inch telescope. English-speaking folk rapidly translated and spread that to mean “canals” – however canali actually means “channels” or “grooves”. Other astronomers, most famously Percival Lowell, ran with that idea and its industrial vibe, ultimately leading to stories of Martians using canals to get water from the ice caps toward the equatorial regions, in a last ditch effort to survive their changing world. But in the early 1900’s, bigger telescopes made the perception of canals give way to clearer pictures of what is really there, shown in the picture at the bottom of this post.

The canals and associated stories of a struggling Martian civilization lent themselves to some very creative science fiction – culminating in H.G. Wells’ The War of the Worlds in the closing years of the 19th century, right on the heels of Percival Lowell’s book Mars. While bigger telescopes eventually gave us a clearer picture of Mars, the stories continued well into the 20th century. Even when a world is as close to us as Mars is, we can’t tell if life exists there without actually visiting. And in the 1970’s, we finally did just that. That’ll be the subject of the next post of course. But first, one last look at the red planet from afar.

Somebody stole the canals!

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