Pluto, Eris and the asteroid Ceres became the first dwarf planets. Unlike planets, dwarf planets lack the gravitational muscle to sweep up or scatter objects near their orbits. They end up orbiting the sun in zones of similar objects such as the asteroid and Kuiper belts .
Many disagreed in 1930 when Pluto was added as our solar system's ninth planet. The debate flared again in 2005 when Eris -- about the same size as Pluto -- was found deep in a zone beyond Neptune called the Kuiper Belt. Was it the 10th planet?
Tuesday, 13 December 2011
Asteroids are rocky, airless worlds that orbit our sun, but are too small to be called planets. Tens of thousands of these "minor planets" are gathered in the main asteroid belt, a vast doughnut-shaped ring between the orbits of Mars and Jupiter. Asteroids that pass close to Earth are called Near-Earth Objects (NEOs).
Tuesday, 29 November 2011
Everyone knows the Earth revolves around the Sun, which takes a year, and the Moon revolves around the Earth, which takes just under a month. So why, then, don't we have 12 solar eclipses and 12 lunar eclipses a year?
If you didn't know any better, you'd expect that each time the Moon passes between the Earth and Sun, its shadow would fall on the Earth, creating a solar eclipse, while each time the Moon passed behind the Earth -- into Earth's shadow -- you'd create a lunar eclipse. So why doesn't this happen?