The Canals of Mars.

Giovanni Schiaparelli was an astronomer from Milan. He discovered that meteor showers co-incided with the Earths passage through the debris left behind by a comet. He is also the man who is popularly credited with the "discovery" of the canals of Mars.

The year is 1877 and Mars and Earth are at "opposition". The two planets pass around the sun, the Earth moving faster than Mars, they occasionally lap each other, and that close point is an opposition. And being so close, it is the best time for Earth-bound observers to study the outer planets.

 

 Like many other astronomers, Schiaparelli was studying Mars. Using the 8" refractor at the Milan Observatory Schiaparelli noticed that when the seeing was good he could just make out, on the edge of vision itself, fine straight lines or striations.

When Schiaparelli made to announce his observations, he used the Italian word canalii meaning some kind of natural channel or groove. Naturally enough, this word was translated into English as "canal". Of course, canals are man-made objects and it was only a matter of time before someone had to ask "Who made the canals on Mars?"

 

Schiaparelli unfortunately  added fuel to the fire. Further observations of his showed that the canals traversed Mars, going from the polar caps all the way to dark patches, which to use the analogy of the moon, were considered "seas". Astronomers already knew that Mars' polar caps changed with the seasons, and that the appearance of the dark seas also changed. Schiaparelli surmised that perhaps the canals were (natural) outlets for Martian polar melt-water? Others surmised that maybe the changing appearance on the seas was actually a reflection of an increase in the growth of plants on the shore.

Schiaparelli knew his hypothesis (the natural channels caused by melt water) was extreme, yet by the end of the 19th Century popular writing on the subject had been unleashed. Straight canals equaled artificial structures created by someone. Or something.

 

From what was known about Mars, that it was a small arid world with a thin atmosphere, the new perception of canalii as canals and hence artificial structures, a view began to be formed of life, of the kind of society that would exist on Mars: beings grappling with the fact that their world was dying had constructed enormous aqueducts to collect the polar melt-water and channel it to the warmer equatorial regions where they would irrigate plants. Astronomers readily estimated the size of the canals around 50km to 150km wide. 

 The efforts required to build the canal network require the resources of an entire planet, therefore Martian society was peaceful and united. The engineering effort required the applications of scientific thought and progress. All of this a complete reflection of the 19th century psyche.

 

At the forfront of this was Percival Lowell. From wealthy old money, he built the Lowell Observatory, still in exstance today, and place where Clyde Tombaugh discovered Pluto. Lowell  built his observatory to examine Mars specifically, and to support his theories about the dying society struggling on it's surface. But trouble began for Lowell as soon as he started looking at Mars, for it would seem that different observers around the world, saw different canals. Although there was some consensus on a few canal features, many of the finely detailed markings were difficult to repeatedly see, or they just plain vanished from sight.

 

In spite of Lowell's persistence, the arguments began to swing away from the idea of a dying civilisation on Mars, eking out the last of it days. The explanation? The Martian canals were nothing more than an optical illusion caused by the eye and brain trying to make sense of fine detail almost beyond the resolution of the eye. Newspaper pictures and modern computer printers take advantage of this fact, by making patterns of dots too small to resolve individually, yet seem from a distance our brain blends them into whole pictures.

To give you a taste of the difficulties that these early astronomers were working under, try and draw the Moon, without using any kind of optical aid at all, then compare it with a moon map. Believe it or not, you will see more detail on the moon this way than any astronomer has ever seen with their own eyes looking at the planets through a telescope.

However the debate persisted well into the 20th Century and it wasn't until the launch of the Mariner series of probes to Mars that the matter was settled decisively. There were no canals. The surface of Mars is an arid cratered wasteland.

But in an ironic twist, we are now reasonably sure that Mars once had vast oceans that sculpted and shaped much of its surface.