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

While the composition of gas and dust in a molecular cloud is fairly uniform, everything changes once a star begins to form.

This may explain the strange properties of the orbits of our solar system's planets, which are not quite perfectly circular, and all lie on slightly different planes. NASA artist’s conception of ...

Stargazers will be treated to a rare alignment of seven planets on 28 February when Mercury joins six other planets that are already visible in the night sky. Here's why it matters to scientists.

All seven of the other planets in our solar system are about to become visible at once in a great planetary alignment – here’s how to spot the celestial show ...