If your southern horizon is not obscured by trees, you can see rust-red Mars partway up the sky around midnight this month and next. From our point of view it’s edging into the northern part of the constellation Scorpio, roughly 55 million miles from Earth, at present.

Mars has amazed humans for millennia, at least. It took thousands of years just to get its orbit figured out. The ancient astronomers assumed the planets, being divinities or the signs of divinity, travel in perfect circles around the Earth, and so they based their calculations of orbits on this. Their math was pretty good but approximate, and in any case, the planets from time to time appear to travel backward in the sky, so loops called epicycles were attached to the circles to keep the descriptions aligned with the observed phenomena.

This got very complicated. But less complicated, seemingly, than suggestions — even in antiquity — that the planets might be circling the sun, not the Earth. Those heliocentric calculations were so arcane, though, that it was more practical to assume that, just as it actually appears, the moon, planets, sun and stars all circle the Earth.

In the 1500s Copernicus took on the task of working out the math that should correspond to all the planets, including the Earth, orbiting around the sun. His model was pretty convincing to many astronomers of the time, though not all, but the orbit of Mars was particularly problematic. No one yet knew why. One of Copernicus’ assistants, Georg Joachim Rheticus, was rumored to have become so maddened by the failure of calculations to accurately describe Mars’ orbit that he summoned a spirit for help. A spirit materialized, grabbed Rheticus by the hair and threw him head first at the ceiling, then let him crash to the floor. “These are the motions of Mars,” it warned. (Rheticus’ father, by the way, was beheaded for practicing sorcery.)

Later, in the early 1600s, Johannes Kepler, with painstaking genius, figured out what Copernicus had not. In fact, Copernicus might not have accepted the physical explanations even if he’d thought of them, because they deviate from the perfection assumed to characterize divinity.

For one thing, Mars’ orbit is not a circle but an ellipse — like all the planets, as it turned out. That was one thing causing problems in the calculations. Kepler also figured out that, contrary to assumptions, the planets do not travel at uniform speeds; they go faster in the parts of their orbits nearer the sun, and slower in the parts farther away. And third, contrary to ancient assumptions, the planets do not orbit all in the same plane out from the sun — if the plane of Earth’s orbit is the central measure, all the other orbits are inclined to it to greater and lesser extents. Kepler’s observation of these three features of the solar system unlocked the basic orbital mechanics that have enabled trips to the moon and robot visits to Mars and beyond.

As telescopes got better and better in the 1700s and 1800s, the view of Mars’ surface got more detailed. In 1877, the Italian astronomer Giovanni Schiaparelli made drawings of Mars showing dark, line-like features that he referred to in Italian as “canali,” meaning channels, but which got translated into English as “canals.” This word ignited the idea that artificial waterways were crisscrossing Mars. The American astronomer and Renaissance man Percival Lowell stoked the idea when he set up a state-of-the-art observatory in Arizona and in the early 20th century wrote several books with detailed illustrations showing the locations not only of canals, but of what Lowell took to be cities on the surface of Mars.

Many astronomers disputed Lowell’s claims, but the idea that Mars was inhabited — at the very least by plants — did not go away easily. As late as 1963, Earl Slipher, a well-credentialed Lowell Observatory astronomer, was insisting that seasonal dark and light fluctuations photographed in Mars’ northern hemisphere had to be vegetation. When Mariner spacecrafts flew by in 1965 and 1969, they took pictures of, essentially, a desert surface, quelling the idea that Mars supports life. It just seemed too dry.

Evidence gathered by orbiters and landers since then, though, suggests there was a lot of liquid water on the Red Planet 3 billion to 4 billion years ago. And lately, evidence has been piling up suggesting that a great deal of water is locked up in ice on and just under Mars’ surface, and that it’s possible some of it turns liquid under certain conditions. This implies, after all, that microbial life might actually exist on Mars. The astronomers are careful not to seem too sure about this.

You can look southward and see it any clear night from now into early summer, 55 million miles or so leeward of the sun. I wonder what else is going on up there that, like elliptical orbits, we just haven’t thought of yet.

Dana Wilde lives in Troy. His book on the stars and planets is “Nebulae: A Backyard Cosmography,” available online in print and e-book editions. He is also a contributor to “Pluto: New Horizons for a Lost Horizon” published by North Atlantic Books. You can contact him at [email protected] Backyard Naturalist appears the second and fourth Thursdays each month.