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

Four planets will be widely visible to the naked eye through part of February, but calling them a 'planetary alignment' may not be the full picture.

Scientists believe that two asteroids might be fragments of long-lost "planetary embryos" from the early solar system.

Take advantage of a special 6-7 planet alignment from Earth's perspective. Planets 'line up' in the skies over California in February.

Does our Solar System have 9 planets or only 8? Astronomers have gone back and forth on that a lot, with Pluto now being classified as a dwarf planet. However, out beyond Neptune there could be ...

The formation of our solar system from a singular nebula raises an intriguing question: why did each planet develop with a ...

Mercury takes only 88 Earth days to orbit the sun.

NASA Scientists discover a fast-moving star and planetary system moving double our solar system speed through the Milky Way.

It is not often that all the planets in the Solar System other than ours are lined up across the night sky for us to see.

Baker said that there are other astronomical events that may be more interesting than the parade of planets. Baker said Mars ...