In January 1910, a breathtaking comet appeared in the morning sky,

brighter than any celestial object but the sun and the moon. It attracted considerable attention

from astronomers, but also from the newspapers and the general public, who had already been

primed to expect a return of Halley's comet this

year. But this comet was not Halley's comet. It was an unexpected rogue comet, one that showed up

just three months before Comet Halley and upstaged the better known comet, coming in brighter and

putting on a much better show.

Welcome to the history of the 20th century.

The 20th century. Episode 54, A Martian Odyssey

In today's episode, I'd like to talk a bit about the astronomy of the early 20th century.

Astronomers of the day knew that the stars were distant suns like our own and could use spectroscopes

to get an idea of their chemical composition. But how stars were organized, if indeed

they were organized, how they were formed and evolved, and what was their fate, these were largely

mysteries in the early 20th century. Indeed, as we have seen, astronomers did not yet understand

how stars generated heat and light.

Within our own solar system, however, the layout of things was pretty well understood.

Astronomers of the day knew that our solar system contains eight planets, Mercury through

Neptune. Observation of their orbits gives you their masses. Spectroscopy

gives you some idea of what their atmospheres are made of. Astronomers knew the basic

facts about asteroids, meteors, and comets. But they had a lot less observational data than we

do today, partly because their equipment was less advanced, and of course they

had 100 years less data to work with than modern astronomers have. So an uncommon event, like the

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