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“What Is a Planet? Why Not Pluto?”

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Credit: NASA/JPL-Caltech/R. Hurt (SSC-Caltech)

The artist's rendition shows Pluto's size in relation to the Earth and the Moon.

A free presentation, titled "What Is a Planet? Why Not Pluto?" will take place at 7:00 p.m. on Tuesday, 7 November 2006, in 100 Thomas Building on the Penn State University Park campus. The program will begin with an introduction by Darren Williams, associate professor of physics and astronomy at Penn State Erie, The Behrend College, and will include a discussion about whether Pluto should remain a planet by several members of the Department of Astronomy and Astrophysics at Penn State. This event is part of the 2006 Friedman Lecture Series in Astronomy.

In August, at a meeting of the International Astronomical Union (IAU), the members voted to approve a definition of planets that led to the “demotion” of Pluto to the status of “minor planet.” The vote was prompted by the 2004 discovery of Eris, an object in the outer solar system that orbits the Sun and is larger than Pluto. Astronomers soon realized that if Pluto remained classified as a planet, there could soon be dozens, or even hundreds, of other planets in our solar system. This situation caused significant turmoil among astronomers and they grappled with the question of what it means to be a planet. In fact, the new minor planet was named after Eris, the Greek goddess of strife and chaos, following the controversial vote. Mercedes Richards, professor of astronomy and astrophysics, was present at the vote and will share her thoughts on that historic occasion.

“We feel that children 10 or older will enjoy this presentation, which should be a bit lighthearted,” says Jane Charlton, professor of astronomy and astrophysics. “Younger children may enjoy it too, if they have a particular interest in planets.”

In a National Geographic News article online, a Texas teacher says the IAU’s decision offers “a wonderful opportunity to teach students that science is a dynamic field.” The full article, including more reactions from teachers and students, is available at:




Darren Williams earned an associate’s degree in physics at Jamestown Community College in 1990, a bachelor’s degree in physics at the University of Pittsburgh in 1992, and a doctoral degree in astronomy and astrophysics at Penn State in 1998. He joined the faculty at Penn State Erie in 1998.

Richards earned a bachelor's degree in physics at the University of the West Indies in Jamaica in 1977, a master's degree in astronomy at York University in Toronto, Canada, in 1979, and a doctoral degree in astronomy at the University of Toronto in 1986. Prior to joining the Penn State faculty in fall 2002, she served on the faculty of the University of Virginia in Charlottesville, where she was appointed assistant professor of astronomy in 1987 and was promoted to associate professor in 1993 and then to professor in 1999. She was a visiting scientist at the Institute for Advanced Study in Princeton, New Jersey, during the 2000-2001 academic year.

This presentation is hosted by the Penn State Department of Astronomy and Astrophysics and is funded largely by the Ronald M. and Susan J. Friedman Outreach Fund in Astronomy. Friedman is a member of the department's Board of Visitors.

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Darren Williams, 814-898-6008, email: dmw145@psu.edu
Mercedes Richards, 814-865-0150, e-mail: mtr@astro.psu.edu
Jane Charlton, 814-863-6040, e-mail: jcharlton@astro.psu.edu

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