* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Groups of Stars
Fermi paradox wikipedia , lookup
Spitzer Space Telescope wikipedia , lookup
Constellation wikipedia , lookup
Corona Borealis wikipedia , lookup
Auriga (constellation) wikipedia , lookup
International Ultraviolet Explorer wikipedia , lookup
Space Interferometry Mission wikipedia , lookup
Corona Australis wikipedia , lookup
Gamma-ray burst wikipedia , lookup
Aries (constellation) wikipedia , lookup
Rare Earth hypothesis wikipedia , lookup
Modified Newtonian dynamics wikipedia , lookup
Aquarius (constellation) wikipedia , lookup
Cassiopeia (constellation) wikipedia , lookup
Andromeda Galaxy wikipedia , lookup
Cygnus (constellation) wikipedia , lookup
Stellar evolution wikipedia , lookup
Globular cluster wikipedia , lookup
Observational astronomy wikipedia , lookup
Perseus (constellation) wikipedia , lookup
Cosmic distance ladder wikipedia , lookup
Open cluster wikipedia , lookup
High-velocity cloud wikipedia , lookup
Future of an expanding universe wikipedia , lookup
Timeline of astronomy wikipedia , lookup
Corvus (constellation) wikipedia , lookup
Stellar kinematics wikipedia , lookup
26.4 When Giovanni Riccioli used a telescope like this one to observe a star in the handle of the Big Dipper, he discovered two stars that orbit each other. Groups of Stars A group of stars that appear to form a pattern as seen from Earth is called a constellation. Stars in a constellation are generally not close to one another. Lie in the same general direction of the sky as seen from Earth. More than half of all stars are a part of star systems Star Systems Most stars occur in groups of two or more. • A star system is a group of two or more stars that are held together by gravity. • A star system with two stars is called a binary star. The two stars orbit each other. Star Systems Sometimes the smaller star in a binary star is too dim to be seen easily from Earth but can still be detected from the motion of the other star. If one star passes in front of the other, blocking some of the light from reaching Earth, the star system is called an eclipsing binary. The brightness of an eclipsing binary varies over time in a regular pattern. Star Clusters There are three basic kinds of star clusters: open clusters, associations, and globular clusters. Star Clusters Studying star clusters is useful because all the stars formed together in the same nebula, so they are about the same age and the same distance from Earth. Astronomers plot the stars of a cluster on an H-R diagram to estimate the cluster’s age. Star Clusters A. The Pleiades are an open star cluster that is visible to the unaided eye. B. 47 Tucanae is a spectacular globular cluster that is visible in southern skies. Star Clusters An open cluster has a disorganized or loose appearance and contains no more than a few thousand stars that are well spread out. Open clusters often contain bright supergiants and gas and dust clouds. Associations are temporary groupings of bright, young stars. In time, gravity from nearby stars breaks these groups apart. Associations are typically larger than open clusters. Star Clusters A globular cluster is a large group of older stars. Globular clusters usually lack sufficient amounts of gas and dust to form new stars. They are spherical and have a dense concentration of stars in the center. Can contain more than a million stars. Usually do not have short-lived blue stars because these stars have already died out. Astronomers estimate that the oldest globular clusters are about 12 billion years old. Thus, the universe must be at least that old. Galaxies Astronomers classify galaxies into four main types: spiral, barred-spiral, elliptical, and irregular. Galaxies A galaxy is a huge group of individual stars, star systems, star clusters, dust, and gas bound together by gravity. • There are billions of galaxies in the universe. • The largest galaxies consist of more than a trillion stars. Galaxies vary widely in size and shape. Galaxies Spiral and Barred-Spiral Galaxies Spiral galaxies have a bulge of stars at the center, with arms extending outward like a pinwheel. • These spiral arms contain gas, dust, and many bright young stars. • The Milky Way is a spiral galaxy. Galaxies Some spiral galaxies have a bar through the center with the arms extending outward from the bar on either side. These are called barred-spiral galaxies. Galaxies Elliptical Galaxies Elliptical galaxies are spherical or oval, with no trace of spiral arms. • Elliptical galaxies come in a wide range of sizes. • Elliptical galaxies have very little gas or dust between stars. They contain only old stars. Galaxies Irregular Galaxies A small fraction of all galaxies are known as irregular galaxies. Irregular galaxies have a disorganized appearance. They have many young stars and large amounts of gas and dust. Irregular galaxies come in many shapes, are typically smaller than other types of galaxies, and are often located near larger galaxies. Galaxies A. B. C. D. A spiral galaxy in the constellation Coma Berenices A barred-spiral galaxy in the Fornax cluster Elliptical galaxy M87 An irregular galaxy with many areas of star formation Our Galaxy The Milky Way Galaxy The Milky Way galaxy has an estimated 200 to 400 billion stars and a diameter of more than 100,000 light years. Every individual star that you can see with the unaided eye is in our galaxy. The solar system lies in the Milky Way’s disk within a spiral arm, about two thirds of the way from the center. Our Galaxy In a side view, the Milky Way appears as a flat disk with a central bulge. An overhead view of the Milky Way shows its spiral shape. Location of solar system Central bulge Nucleus Overhead View of Our Galaxy Disk of spiral arms containing mainly young stars Halo containing oldest stars Central bulge containing mainly older stars Nucleus Side View of Our Galaxy Our Galaxy The Milky Way’s flattened disk shape is caused by its rotation. The sun takes about 220 million years to complete one orbit around the galaxy’s center. Recent evidence suggests that there is a massive black hole at our galaxy’s center. Stars are forming in the galaxy's spiral arms Other Galaxies Quasars Quasars are the enormously bright centers of distant, young galaxies. Identified by spectra Quasars produce more light than hundreds of galaxies the size of the Milky Way. What makes a quasar so bright? The most likely explanation involves matter spiraling into a super-massive black hole with the mass of a billion suns.