In 1892, we can note the last human eye discovery of a solar system satellite. The eye belonged to Edward Emerson Barnard who, working at the Lick Observatory in California, found a fifth satellite of Jupiter. Hereafter, every subsequent satellite discovery was made by the comparison of photographic or other images. Barnard, while heralding the end of a sentimental astronomical age, actually had one foot in the new.
It’s interesting that Barnard worked as a photographer’s assistant from age nine, and was a pioneer in the developing use of photographic imagery for astronomy. He was also a crackerjack observing scientist, having discovered over a dozen comets. In addition, he contributed a great deal by optical assessments of distant stars and nbeula far beyond the solar system.
So almost three centuries after Galileo’s momentous revelation of “Medicean Stars,” the king of planets now had a fifth moon, now the 21st known to human astronomers.
Meet Amalthea, in two images from Galileo probe, not the astronomer:
The Galileo probe of the 90’s didn’t uncover very much about this inner satellite. The fifth discovered orbiter of Jupiter is also, fittingly enough, the fifth largest of Jupiter’s moons. But Amalthea is still significantly smaller than next-largest Europa, measuring a potato-shaped 160 by 100 by 90 miles. At the close of the 19th century, that made it the third-smallest known satellite, larger only than the two city-sized moons of Mars.
And the name? Amalthea wasn’t official until 1975, but it seemed appropriate that a close moon be named after the goat shepherdess that nursed the infant god Zeus (Greek mythology). Some variations have Amalthea as the goat nursing the future king of gods with her own milk. At any rate, Amalthea is a light and fluffy moon, about the same weight as a 160 mile-long ice cube. It might be all ice. Or it could be a loose conglomeration of rock rubble with some empty spaces inside.
Imaginative photographers will pick up the mantle of discovery from here. In the next installment, we’ll see how Jupiter netted a bevy of new moons, but every other outer planet added known companions in the 1900’s, even Pluto.