The Milky Way is a spiral galaxy with a bulge at its centre and a surrounding spiral disc of stars, gas and dust.
Image: A Spitzer Space Telescope infrared image of hundreds of thousands of stars in the Milky Way's core (credit: NASA/JPL-Caltech)
The Sun is one of countless stars in our galaxy.
Patrick Moore and his guests discuss galaxies.
Sir Patrick Moore and his guests explain what galaxies are and discuss some of their interesting features.
Patrick Moore describes some sights in the Milky Way.
Sir Patrick Moore and Chris Lintott describe some of the beautiful sights in our galaxy, the Milky Way.
Researchers find a black hole at the galaxy's centre.
Professor Reinhard Genzel explains how he found strong evidence of a supermassive black hole at the centre of our galaxy, the Milky Way.
Patrick Moore discusses the Magellanic Clouds.
Sir Patrick Moore discusses the Magellanic Clouds, supernovae, and other sights.
The Earth makes a dangerous journey through the galaxy.
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 our Solar System.[nb 1] Its name “milky” is derived from its appearance as a dim 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 Latin via lactea, from the Greek γαλαξίας κύκλος (galaxías kýklos, "milky circle"). From Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Up until the early 1920s, most astronomers thought that all of the stars in the universe were contained inside of the Milky Way. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis, observations by Edwin Hubble definitively showed that the Milky Way is just one of many billions of galaxies.
The Milky Way is a barred spiral galaxy some 100,000–120,000 light-years in diameter, which contains 100–400 billion stars. It may contain at least as many planets as well. The Solar System is located within the disk, about 27,000 light-years away from the Galactic Center, on the inner edge of one of the spiral-shaped concentrations of gas and dust called the Orion Arm. The stars in the inner ≈10,000 light-years form a bulge and one or more bars that radiate from the bulge. The very center is marked by an intense radio source, named Sagittarius A*, which is likely to be a supermassive black hole.
Stars and gases at a wide range of distances from the Galactic Center orbit at approximately 220 kilometers per second. The constant rotation speed contradicts the laws of Keplerian dynamics and suggests that much of the mass of the Milky Way does not emit or absorb electromagnetic radiation. This mass has been given the name “dark matter”. The rotational period is about 240 million years at the position of the Sun. The Milky Way as a whole is moving at a velocity of approximately 600 km per second with respect to extragalactic frames of reference. The oldest known star in the Milky Way is at least 13.82 billion years old and thus must have formed shortly after the Big Bang.
Surrounded by several smaller satellite galaxies, the Milky Way is part of the Local Group of galaxies, which forms a subcomponent of the Virgo Supercluster, which again forms a subcomponent of the Laniakea Supercluster.