Blog Archive

An official pronouncement may be coming about the "what is a planet?" debate

Posted by Emily Lakdawalla on 2005/09/21 02:28 CDT

Since the discovery of 2003 UB313, larger than Pluto, there's been a lively debate going on in many places about what makes a planet. There's now an article in Nature talking about a proposal that would address the controversy

Pluto: The Discovery of a Planet

Posted by Amir Alexander on 2005/02/18 11:00 CST

To mark the 75th anniversary of the discovery of the planet Pluto, The Planetary Society presents to its readers the remarkable story of the discovery.

The Discovery of a Planet, Part 6: From Pluto to Sedna

Posted by Amir Alexander on 2005/02/17 11:00 CST

74 years after Clyde Tombaugh discovered Pluto as a faint dot on a pair of photographic plates, a modern group of astronomers made another remarkable discovery. On March 15, 2004, Michael Brown of Caltech, Chad Trujillo of the Gemini Observatory, and David Rabinowitz of Yale announced the discovery of Sedna – the furthest object ever detected in the Solar System.

The Discovery of a Planet, Part 5: The Aftermath

Posted by Amir Alexander on 2005/02/16 11:00 CST

The discovery of Planet X was announced to the world on March 13, 1930, which marked the anniversary of William Herschel’s discovery of Uranus in 1781 as well as Percival Lowell’s birthday. The observatory’s communiqué emphasized that the discovery was no coincidence, but the vindication of Lowell’s predictions made years before.

The Discovery of a Planet, Part 4: Clyde's Search

Posted by Amir Alexander on 2005/02/15 11:00 CST

Since his teenage years Clyde Tombaugh had been an avid amateur astronomer and a gifted telescope builder. Based on instructions contained in an article from a boy’s Sunday school paper, he built a series of telescopes of increasing power and quality on the family farm.

The Discovery of a Planet, Part 3: Planet X

Posted by Amir Alexander on 2005/02/14 11:00 CST

The discovery of Neptune accounted for nearly all the unexplained motions of the outer planets of the Solar System. Nevertheless, several astronomers insisted that some unexplained residual motions remained, pointing to the presence of a ninth planet beyond the orbit of Neptune.

The Discovery of a Planet, Part 2: Out of the Six-Planet World

Posted by Amir Alexander on 2005/02/13 11:00 CST

Since humans first set their eyes to the stars, they noticed that a few of these bright objects behaved differently from the others. Whereas all the stars moved together, revolving around the Earth once every 24 hours, five appeared to move within the firmament among the other stars. Accordingly, they were named “planets,” meaning “wanderers” in Greek.

The Discovery of a Planet, Part 1: The Blinking Image

Posted by Amir Alexander on 2005/02/12 11:00 CST

February 18, 1930, was a cloudy day at the Lowell Observatory, on top of Mars Hill in Flagstaff, Arizona. 22 year old Clyde Tombaugh was hard at work, peering through the lens of an ancient-looking brass-colored device. The instrument, known as a “blink comparator,” mounted two large photographic plates.