Our galaxy is thought to be at least 100,000 light years across and have more than 100 billion stars.
The Milky Way is a spiral galaxy with a bulge at its centre and a surrounding spiral disc of stars, gas and dust.
The entire galaxy rotates around a central axis. Since the dinosaurs died out about 65 million years ago, the Sun is estimated to have travelled about a third the way around the Milky Way's centre.
Image: A Spitzer Space Telescope infrared image of hundreds of thousands of stars in the Milky Way's core (credit: NASA/JPL-Caltech)
Astronomers Pete Lawrence and Paul Abel discuss some of the highlights of summer night skies in the northern hemisphere. The summer months are an ideal time to view the Milky Way galaxy and to look at the constellation of Sagittarius which contains a pattern of stars that looks a bit like a teapot.
Astronomer Pete Lawrence explains how to find our galaxy in the summer night sky.
Astronomer Pete Lawrence explains how stargazers in the northern hemisphere can find the Milky Way in the summer night sky using a pattern of stars called the summer triangle.
Sir Patrick Moore notes that when we look at the prominent winter constellation Orion, we do not see bright galaxies. Dr Chris Lintott explains that during the winter months, we are looking through a stunted spiral arm of the Milky Way known as the Orion Spur. Because we are looking through our galaxy, it is difficult to see galaxies out in the wider Universe. But our view of the night sky changes in the spring and autumn.
In the late 1960s, astronomers use radio waves to build up a picture of our galaxy, the Milky Way.
The Earth makes a dangerous journey through our galaxy, the Milky Way, periodically passing through areas of dense stars. The influence of other stars' gravity sends comets in the outer Solar System hurtling towards Earth.
The Milky Way is the galaxy that contains Earth.[a] This name derives from its appearance as a dim "milky" glowing band arching across the night sky, in which the naked eye cannot distinguish individual stars. The term "Milky Way" is a translation of the Classical Latin via lactea, from the Hellenistic Greek γαλαξίας κύκλος (pr. galaktikos kyklos, "milky circle").
The galaxy has this appearance because it is a disk-shaped structure that is being viewed from inside. Earth is located within the galactic plane of this disk, around two thirds of the way out from the center, on the inner edge of a spiral-shaped concentration of gas and dust called the Orion–Cygnus Arm. The concept of this faint band of light being made up of stars was proven in 1610 when Galileo Galilei used his telescope to resolve it into individual stars. In the 1920s observations by astronomer Edwin Hubble showed that the Milky Way was just one of around 200 billion galaxies in the observable universe.
The Milky Way is a barred spiral galaxy 100,000–120,000 light-years in diameter containing 200–400 billion stars. The galaxy is estimated to contain at least as many planets, 10 billion of which could be located in the habitable zone of their parent star. Depending on its structure the entire galaxy has a rotational rate of once every 15 to 50 million years. The galaxy is also moving at a velocity of 552 to 630 km per second, depending on the relative frame of reference. It is estimated to be about 13.2 billion years old, nearly as old as the Universe. The Milky Way is part of the Local Group of galaxies.
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