Tycho Brahe’s Star

¡SkyCaramba! Weekly astronomy blog for the week ending November 8, 2014

Some people look to the skies for signs of changes to come. Sometimes, a celestial event ushers in change. The mysterious appearance of a new star in November 1572 satisfied both causes.

One night, people all over the northern hemisphere saw a star where they had seen none before. Cassiopeia looks like an M or a W depending on where it is as it circles the north celestial pole. In story telling, its familiar outline marks a throne into which a vain queen from an ancient kingdom is chained. No one expected to see a sparkling new jewel there.

For about 2,000 years, various educated people had thought the heavens were mostly unchanging. In their view, all the stars that would ever exist were already up there and weren’t going anywhere. Planets, the sun, and the moon obviously moved, but people accepted that. Comets were a little hard to explain. Nevertheless, by the late 16th century, it was a very common view that stars were permanent, fixed in place, and not changing.

Suddenly, to the people alive in 1572, there appeared a blatant challenge to the idea. Astronomers thought that since stars don’t appear or disappear, the newcomer must be some other kind of fairly close object like the moon or planets. There was no denying that astronomers didn’t know everything yet—even though in some places government policy treated them like they did. If not for being visible to the naked eye for more than a year, some astronomers could have been imprisoned for saying a star suddenly showed up one night.

Tycho Brahe began observing the star on November 11. He wasn’t the only notable astronomer to make drawings and descriptions as the star slowly faded from view over the next year-and-a-half. But his observations have become so famous, it’s often called Tycho’s Star. He described it in 1573 in a work titled De Stella Nova. In Latin, that means on the new star. By itself, the word nova came to mean new star.

Brahe knew the new star couldn’t be close. It had to be far away like the other stars. An object that’s close shows a parallax—the appearance of a shift in position compared to what’s behind it as the observer moves from place to place. The new star didn’t move at all the way the planets and the moon move in front of the stars. To Brahe, science had been wrong about the stars being unchanging.

Let us also learn a lesson Brahe didn’t. A practitioner of astrology, he believed the new star foretold a period of peace followed by one of war. French theologian Theodore Beza believed it was a new Star of Bethlehem and Christ would soon return. Various others made various other predictions. And since they couldn’t all be right, people became a little more likely to question whether astrology had any merit at all.

X-ray star of Tycho's Star remnantIn the centuries since the nova of 1572 adorned our skies, science has learned that stars form and die over the course of millions of years. A nova isn’t a new star at all, but a rather old one in its death throes. With modern telescopes, someone discovers a nova every few months. The brightest ones—including the one in 1572—are now called supernovae. The changing nature of the distant heavens is fairly common knowledge now.

Not so many people dismiss astrology, however. Quite a lot of people still think it’s the same thing as astronomy. Be assured, the scientific view is that the things that go on in the celestial realm do affect us in very specific and limited ways. If the moon is in Aquarius, it means you can see the moon in Aquarius. And that’s all.