The number of planets that orbit the sun depends on what you mean by “planet,” and that’s not so easy to define ...

Pluto isn't alone—it's part of the Kuiper Belt with possibly hundreds of other planet-sized objects. Because Pluto hasn't ...

Eris is three times more distant than Pluto. And its relationship to Pluto — a world demoted since 2006 from the solar system’s ninth planet to a lowly dwarf planet, in large part due to the ...

And it’s as a dwarf planet that Pluto is taught to students today ... status and you would have to confer the same honor on Eris, a Kuiper Belt object of about the same size, as well as any ...

Saturn, Venus, Neptune, Uranus, Jupiter, Mars and Mercury will be visible in an uncommon planetary alignment this month.

Brown’s team discovered a dwarf planet, Eris, in January 2005. At the time, it appeared to be larger than Pluto. If Pluto hadn’t been demoted, Brown says, hundreds of celestial objects would ...

Pluto may not be a planet any more, but you still have a chance to see the distant dwarf planet at one of Michigan's ...

Clyde Tombaugh didn't set out to discover Pluto when he sent his sketches of the night sky to Lowell Observatory in Flagstaff ...

Because of this, Pluto no longer fit the definition of a full-fledged planet and was reclassified as a dwarf planet on August 24, 2006. In 2005, astronomers discovered Eris, a celestial body in ...

An amateur astronomer discovered Pluto 95 years ago today. The former planet will complete an orbit in another 153 years.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute With Pluto's "demotion" to dwarf planet status ... along with bodies like Eris, Ceres and Pallas.