Chapter 27 Stars and Galaxies Section 3 Star Groups Notes 27-4

Constellations Star pattern or regions Stars appear to be close Stars that make up one constellation are not all the same distance away from the earth Individual stars in constellation don’t seem to move Whole constellation do move across the sky from night to night

Constellations 88 constellations are recognized Named for animals (real or imaginary) Draco (dragon), Ursa Major (great bear) Named for gods or heroes Hercules, Orion

Constellations Used to divide the sky into sections like a map of the United States Use the constellations to find other stars and galaxies Stars in constellations are labeled according to apparent magnitude Brightest = Alpha (α) Second brightest = Beta (β) Stars can also have names that don’t relate to the constellation at all Alpha Scorpii is also called Antares

Galaxies Large scale groups of stars bound together by gravity Typically they are 100,000 ly in diameter and have 100 billion stars Contain nebulae Can reflect light from nearby stars or produce its own light from hot gases Some are dark; absorb light from stars behind them

Galaxies Nearest galaxies to us (Milky Way) Large Magellanic Cloud Small Magellanic Cloud 150,000 ly away There are 17 other galaxies that are within 3 million ly of the Milky Way Called the Local Group

Galaxies Spiral: Has a nucleus of bright stars and flat arms that spiral out from it Contains young stars, gas and dust Some have a bar of stars that runs through the center Called barred spiral galaxies Milky Way is a spiral galaxy

M74 – Spiral Galaxy

Galaxies Elliptical: Can be nearly spherical to a flatten disk Have a very bright center (but no arms) No young stars Contains little dust or gas

M87 – Elliptical Galaxy Also called Virgo A

Galaxies Irregular: Has no particular shape Are smaller and fainter Believed to have no enough gravity to organize the stars Could also be from two galaxies colliding Stars are unevenly distributed

IC10 – Irregular Galaxy

Milky Way Cloud like band that stretches across the sky Spiral Galaxy Each star is orbiting around the center Diameter = 100,000ly Thickness (center) = 2,000 ly Sun’s distance from center = 30,000 ly Revolves 250 km/s Completes one revolution in about 200 million yrs

Milky Way Galaxy

Milky Way Star clusters Globular cluster: spherical shape with many more stars than open clusters Found at the center of the galaxy Open cluster: loosely shaped with less stars than globular clusters Found on the arms of the galaxy

Milky Way Binary Stars Multiple star systems Pair of stars that revolve around each other Used to determine stellar masses

Universe Around 12-15 billion years old Big Bang occurred that long ago All matter moved outward Gravity condensed some matter into galaxies and other masses Galaxies are still moving away

Universe Quasar: star-like objects that formed 12 billion years ago (12 billion ly away from Earth) Give off radio and x-rays Some of the first objects to form after the Big Bang Evolved into galaxies Read pg. 565 “Earth Beat”

Quasar