Bat-Men On The Moon!
One August morning in 1835, readers of the New York Sun were astonished to learn that the Moon was inhabited. Three-quarters of the newspaper's front page was devoted to the story, the first in a series entitled "Great Astronomical Discoveries Lately Made by Sir John Herschel, L.L.D, F.R.S, &c At The Cape of Good Hope." Herschel, a well-known British astronomer, was able "by means of a telescope of vast dimensions and an entirely new principle," the paper reported, to view objects on the Moon as though they were "at the distance of a hundred yards." Each new story in the six-part series reported discoveries more fantastic than the last.

Herschel's telescope revealed lunar forests, lakes and seas, "monstrous amethysts" almost a hundred feet high, red hills and enormous chasms. Populating this surreal landscape were animals resembling bison, goats, pelicans, sheep—even unicorns. Beavers without tails walked on two legs and built fires in their huts. A ball-shaped amphibian moved around by rolling. There were moose, horned bears and miniature zebras. But the biggest surprise of all was reserved for the fourth article in the series. Herschel and his team of astronomers had spotted humanoids: bipedal bat-winged creatures four feet tall with faces that were "a slight improvement" on the orangutan's. Dubbed Vespertilio-homo (or, informally, the bat-man), these creatures were observed to be "innocent," but they occasionally conducted themselves in a manner that the author thought might not be fit for publication.

The Sun also described massive temples, though the newspaper cautioned that it was unclear whether the bat-men had built them or the structures were the remnants of a once-great civilization. Certain sculptural details—a globe surrounded by flames—led the Sun's writer to wonder whether they referred to some calamity that had befallen the bat-men or were a warning about the future.

Reaction to the series—an effort to boost circulation, which it did—ranged from amazed belief to incredulity. Herschel himself was annoyed. In a letter to his aunt Caroline Herschel, also an astronomer, he wrote, "I have been pestered from all quarters with that ridiculous hoax about the Moon—in English French Italian & German!!" The author of the piece was most likely Richard Adams Locke, a Sun reporter. The newspaper never admitted it concocted the story. It's tempting to think that we're immune to such outlandish hoaxes today, and perhaps we are. But a passage from the series reminds us that we're not as different from our forebears of almost 200 years ago as we might think. When Herschel made his supposed optic breakthrough, the Sun reported, a colleague leapt into the air and exclaimed: "Thou art the man!"

Planet Vulcan Found!
Vulcan is best known today as the fictional birthplace of the stoic Mr. Spock on "Star Trek," but for more than half a century it was considered a real planet that orbited between Mercury and the Sun. More than one respectable astronomer claimed to have observed it.

Astronomers had noticed several discrepancies in Mercury's orbit. In 1860, French mathematician Urbain Le Verrier speculated that an undetected planet exerting a gravitational pull on Mercury could account for the odd orbit. He named it Vulcan.

An astronomer named Edmond Lescarbault said he had spotted the planet the previous year. Other astronomers pored over reports of previous sightings of objects crossing in front of the Sun. Occasional sightings of planet-like objects were announced, each prompting astronomers to recalculate Vulcan's orbit. After the solar eclipse of 1878, which gave astronomers a rare opportunity to see objects normally obscured by the Sun's glare, two astronomers reported they had seen Vulcan or other objects inside Mercury's orbit.

Le Verrier was awarded the Légion d'honneur for predicting the location of a real planet: Neptune. He died in 1877 still believing he had also discovered Vulcan. It took until 1915 and improved photography and the acceptance of Einstein's general theory of relativity, which explained Mercury's orbital discrepancies, for the idea to be laid to rest. The observations of the phantom planet were either wishful thinking or sunspots.

Martians Build Canals!
Percival Lowell peered through a telescope on an Arizona hilltop and saw the ruddy surface of Mars crisscrossed with canals. Hundreds of miles long, they extended in single and double lines from the polar ice caps. Bringing water to the thirsty inhabitants of an aging planet that was drying up, the canals were seen as a spectacular feat of engineering, a desperate effort by the Martians to save their world.

Lowell was an influential astronomer, and the canals, which he mapped with elaborate precision, were a topic of scientific debate during the early 20th century. We know now that the canals didn't exist, but how did this misperception begin?

In 1877, Giovanni Schiaparelli, an Italian astronomer, reported seeing canali on the surface of Mars. When his report was translated into English, canali, which in Italian means channels, was rendered as canals, which are by definition man-made.

Lowell's imagination was ignited by Schiaparelli's findings. In 1894, Lowell built an observatory in Flagstaff, Arizona, and focused on Mars. Other astronomers had noticed that some areas of the planet's surface seemed to change with the seasons—blue-green in the summer and reddish-ocher in the winter. These changes seemed to correspond with the growing and shrinking of the polar ice caps. Lowell believed that the melting caps in summer filled the canals with water that fed large areas of vegetation. He filled notebook after notebook with observations and sketches and created globes showing the vast network of waterways built by Martians.

The intricacy of Lowell's canal system is all the more mystifying because it doesn't seem to correspond to any actual features on the planet—yet he apparently saw the same canals in exactly the same places time after time. Even in Lowell's day, most other astronomers failed to see what he saw, and his theory fell into disrepute among most of the scientific community (though the public continued to embrace the notion). To this day, no one knows whether Lowell's maps were the result of fatigue, optical illusions or, perhaps, the pattern of blood vessels in his eye.

Like any romantic idea, belief in Martian canals proved hard to abandon. The possibility of life on the planet closest to ours has fascinated us for centuries and continues to do so. Lowell's canals inspired science fiction writers including H.G. Wells and Ray Bradbury. It took the Mariner missions to Mars of the 1960s and 1970s to prove that there are no canals on the Red Planet.

The Earth Is Hollow!
(and we might live on the inside)
Imagine the earth as a hollow ball with an opening at each pole. On its inner surface are continents and oceans, just like on the outer surface. That's the Earth envisioned by Capt. John Cleves Symmes, an American veteran of the War of 1812. He toured the country in the 1820s, lecturing on the hollow Earth and urging Congress to fund an expedition to the polar openings. His hope was that Earth's inner surface would be explored and that trade would be established with its inhabitants.

The hollow Earth theory wasn't entirely new—the idea of open spaces inside Earth had been suggested by ancient thinkers including Aristotle, Plato and Seneca. Caves and volcanoes gave the concept plausibility, and legends and folktales abound with hidden civilizations deep below the crust.

In 1691, to explain variations in Earth's magnetic poles, royal astronomer Sir Edmond Halley, better known for recognizing the schedule of a brilliant comet, proposed a hollow Earth consisting of four concentric spheres. The interior must be lit and inhabited, he said; the idea of the Creator failing to populate the land and provide its populace with life-giving light seemed inconceivable. Halley proposed a luminous substance that filled the cavity, and he attributed the aurora borealis to its escape through the crust at the poles.

To make a weird idea even weirder, Cyrus Teed, a 19th-century physician, alchemist and experimenter with electricity, concluded that the world was not only hollow but also that human beings were living on its inner surface. He got the idea in 1869, when an angelic vision announced (after Teed had been shocked into unconsciousness by one of his experiments) that Teed was the messiah. According to the angel, the Sun and other celestial bodies rose and set within the hollow Earth due to an atmosphere that bent light in extreme arcs. The entire cosmos, he claimed, was contained inside the sphere, which was 8,000 miles in diameter. Teed changed his name to Koresh (the Hebrew form of "Cyrus"), founded his own cult (Koreshanity) and eventually built a compound for his followers, who numbered 250, in southwestern Florida. The compound is now preserved by the state of Florida as the Koreshan State Historic Site and draws tens of thousands of visitors every year.

Venus Attacks!
In 1950, Immanuel Velikovsky published Worlds in Collision, a book that claimed cataclysmic historical events were caused by an errant comet. A psychoanalyst by training, Velikovsky cited the Old Testament book of Joshua, which relates how God stopped the Sun from moving in the sky. Moses' parting of the Red Sea, Velikovsky claimed, could be explained by the comet's gravitational pull. He theorized that in 1500 B.C., Jupiter spewed out a mass of planetary material that took the form of a comet before becoming the planet Venus.

Velikovsky was one in a long line of catastrophists, adherents of the theory that sudden, often planet-wide cataclysms account for things like mass extinctions or the formation of geological features. His book is remarkable not so much for its theories—which are unexceptional by catastrophist standards—but for its popularity and longevity. A New York Times best seller for 11 weeks, it can be found on the science shelves of bookstores to this day and enjoys glowing reviews on some Web sites.

Worlds in Collision was met with derision from scientists. Among other problems, the composition of Venus and Jupiter are quite different, and the energy required for ejecting so much material would have vaporized the nascent planet. At a 1974 debate sponsored by the American Association for the Advancement of Science, Carl Sagan, the popular astronomer, was among the panelists opposing Velikovsky. But the attacks may have strengthened Velikovsky's standing; he struck some people as an underdog fighting the scientific establishment.

Velikovsky's ideas seemed radical a half century ago—most astronomers assumed that planetary change occurred at a slow, constant rate. His remaining adherents point to the asteroid impact that killed most of the dinosaurs 65 million years ago as evidence he was ahead of his time.

Erik Washam is the associate art director for Smithsonian.