Astronomy News

What is the definition of a planet? Technically, there was never a scientific definition of the term Planet before 2006. When the Greeks observed the sky thousands of years ago, they discovered objects that acted differently than stars. These points of light seemed to wander around the sky throughout the year. We get the term "planet" from the Greek word "Planetes" - meaning wanderer.

What is a galaxy? Galaxies are large systems of stars and interstellar matter, typically containing several million to some trillion stars, of masses between several million and several trillion times that of our Sun, of an extension of a few thousands to several 100,000s light years, typically separated by millions of light years distance. They come in a variety of flavors: Spiral, lenticular, elliptical and irregular. Besides simple stars, they typically contain various types of star clusters and nebulae.

What is Dark Matter?The story of dark matter is best divided into two parts.  First we have the reasons that we know that it exists.  Second is the collection of possible explanations as to what it is.

Why the Universe Needs Dark Matter

We believe that that the Universe is critically balanced between being open and closed.  We derive this fact from the observation of the large scale structure of the Universe.  It requires a certain amount of matter to accomplish this result.  Call it M.

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).