Chapter 26.4 Groups of Stars

Groups of Stars: Constellations Stars that seem to form a picture. These stars are may or may not be close to one another.

Constellations Circumpolar – “Circle” North and South Pole Can be seen all year Ex: Ursa Major (Big Bear with the Big Dipper), Draco (Dragon) Polaris = North Star

Constellations Zodiac – “Birthday” Constellations “Move” on the ecliptic line – and can only be seen during certain months. The month of your birthday, you cannot see your zodiac constellation because it is BEHIND the sun.

Binary Stars – Two stars orbit around a shared center of mass Alcor and Mizar in the Dipper appear as double stars Over 65% of stars may have companion stars. “Star System” 2 or more stars orbit around a center of mass.

Other groups of stars Open Clusters – Pleiades A cluster of 100s s of stars – in this case young blue stars Closed (Globular) Clusters Older stars densely packed.

Galaxies = Groups of millions - trillions stars that are held together by gravity. Milky Way Stats LY across LY thick 5 Spiral Arms Our sun is 2/3 the way out on the Orion spiral arm. Moves around center at a speed of 500,000 mi/hr (It takes 200 million yrs to complete one rotation) Try this simulation: space.stsci.edu/resources/explorations/g alaxies-galore/build/index.html

Types of Galaxies Spiral A. Central Bulge – Most stars are located here. Old stars are concentrated here. Possible location for BLACK HOLES B. Disk – Flattened pancake of young stars C. Arms – Lanes that radiate from center – Young blue stars D. Halo – surrounds bulge & arms. Contains old stars, globular clusters, & possibly dark matter. Spirals have a good deal of dust & gas A A B B C D

Types of Galaxies - Ellipitical The giant elliptical galaxy M87 (AAO) Elliptical Galaxies are shaped like ovals or footballs. They are dense and the stars in them are VERY OLD. Stars “swarm” around like bees inside. Types of Galaxies Spiral-Barred –

Types of Galaxies – Irregular No real shape Common in distant (early) universe Younger stars, gas, & dust Sometimes a result of galaxy collisions Test your knowledge of galaxy types here!:

Quasars Very distant objects that release energy in outputs = to that of hundreds of GALAXIES combined Quasars may be powered by SUPERMASSIVE black holes that “accrete” galaxies.

Galaxy Collisions Simulations: The Milky Way is predicted to collide with our larger neighbor Andromeda in about 5 billion years. (It is approaching us at 670,000 mi/hr). Eventually they may merge to form an elliptical galaxy. Because stars are so far apart – it may have no affect … then again – we could get ejected out of our “place” on the Orion arm due to collision.

Deep Space Hubble Telescope takes a picture of deep space. Each “star” is actually an entire galaxy made up of billions of stars. Many of these galaxies are over 13 billion LY away. It took light 13 billion years for the light to travel to us.

Groupings of Galaxies The Milky Way orbits in a circle with a group of neighboring galaxies called our LOCAL GROUP. These GROUP of GALAXIES orbits with other GROUPS of GALAXIES in a SUPERCLUSTER Our Official Address: Planet Earth Sol Solar System Orion Arm, Milky Way Galaxy Local Group Virgo Supercluster Observable Universe This is Andromeda – one of the spiral galaxies in our Local Group (2.2 million LY)

Magnitude = Star Brightness Some stars seem brighter than others. Brightness (Magnitude) depends on.. a. Closeness (closer brighter) b. Size (bigger = brighter) c. Temperature (hotter = brighter) Magnitude Scale Very Bright BrightDim Absolute Magnitude = How bright something REALLY is Apparent Magnitude = How bright it SEEMS (maybe its close)

Magnitude Questions Star A has a magnitude of 2 Star B has a magnitude of 1 1. Which is brighter? 2. Bernard’s Star is one of the closest stars to us. It has a magnitude of 8. What conclusions can you make about Proxima Centauri based on this?

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