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.
Chris Lintott explains why our view of the stars changes throughout the year.
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.
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.
You can see the Milky Way, the 'teapot' and noctilucent clouds.
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.
Painting a picture of the galaxy.
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 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 the Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within the Galaxy. 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 Galaxy 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 Galaxy 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.