Hubble Space Telescope recently snapped an ultra-sharp view of the nucleus (inset) of M31, the Andromeda galaxy (background). The image shows that the galaxy has a double nucleus surrounded by a cluster of bright blue stars, which are quite young. The cluster spans several light-years and contains hundreds of stars. A similar but smaller cluster has been discovered in the nucleus of our own galaxy, the Milky Way. [NASA/ESA/T. Lauer (NOAO)]
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Galileo Galilei is already known as one of the greatest astronomers in history. With his handmade telescopes, he discovered the four largest moons of Jupiter and the phases of Venus. He found that the Milky Way actually consists of countless individual stars, and saw that instead of being smooth, as just about everyone thought, the Moon was covered by jagged mountains, valleys, and craters.
Yet if he’d realized what he was looking at 400 years ago today, Galileo might have burnished his reputation even more. He recorded a small star near Jupiter, which had moved relative to the other stars around it. This pinpoint of light was the planet Neptune, which wasn’t officially discovered until 1846.
Galileo was fascinated by the moons of Jupiter. He’d been watching them for a couple of years, charting their positions and even predicting their motions. And in January 1613, Neptune crept behind Jupiter, sliding across Galileo’s field of view.
His notebooks show that he actually recorded the planet three times over several weeks. It was at a point where it doesn’t move much against the background of stars, so its position relative to the true stars didn’t change by a lot.
One researcher has suggested that Galileo knew he was looking at a possible planet. But Galileo never announced his finding to the rest of the world. Since he kept the mysterious “star” to himself, Neptune remained “undiscovered” for more than two centuries.
Script by Damond Benningfield, Copyright 2012
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