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Stars Chapter 21 The Branches of Earth Science • Astronomy: The study of the planets, stars, and other objects in space. The Branches of Earth Science • Lithosphere: the land masses of earth • Litho means rock The Branches of Earth Science • Hydrosphere: waters of the earth – Hydro means water The Branches of Earth Science Atmosphere: The envelope of gases that surround the Earth as well as space and stars. Tools Used to Study Stars • Spectroscope: Breaks light from a distant star into its characteristic color • SPECTRUM: the band of colors that forms as light passes through a prism • Used to see if galaxies are moving away or toward the earth Tools Used to Study Stars • Types of Telescopes Telescopes: device – Optical that makes distant – Radio objects appear – X-Ray closer – U-V – Infrared Constellations Constellations: group of stars that formed patterns How do They Get Their Name? • Different cultures gave different names to the constellations For Example: The Greeks named constellations according to myths • The same constellation can have different names in different cultures Greek Orion Sumerian Sheep China Three Why are Constellations Important? • Navigation – Sailors use Polaris (North Star) – Important in space navigation • Used to predict the weather. Best Known Constellations • Big Bear or Ursa Major • Very similar to Big Dipper – Has pointer stars to Polaris • Little Bear or Ursa Minor • Very similar to Little Dipper What are Stars Like? • Stars are made up of mostly hydrogen • Stars produce energy through nuclear fusion. Characteristics of Stars • There are 4 major characteristics of starts that scientists use to classify stars • Color & Temperature • Size • Composition • Brightness Color & Temperature • Stars are very Patriotic • A stars color when it comes to color reveals its surface Coldest Red temperature – The surface White temperature is lower than the core temperature Hottest Blue due to nuclear fusion. 5 Categories of Sizes Smallest Neutron (16-20 km diameter) White dwarf (size of Earth) Medium Size (the sun) *MOST STARS* Giant Largest (10-1000 x’s the sun) Super Giant (1000 x the diameter of the sun) The Sizes of Super Giant Stars Look at the size of the sun compared to the stars, it is almost invisible Composition (Chemical Makeup) • Most stars have the same general composition – 73% Hydrogen (Most Common) – 25% Helium (2nd most common) – 2% Other Elements Composition Continued • Scientists use a spectroscope to identify characteristics –Characteristic: Something that identifies an object –Elements have “Fingerprint” color characteristics • They have a unique set of lines in the spectrum Brightness (Also called Magnitude) Depends on… • • Temperature • Size • • Distance Apparent Brightness: the brightness of a star as it appears on Earth. Absolute Magnitude: The amount of light the star actually gives off Measuring Distance to Stars • Light Year- Astronomers use light years to measure the distances between stars –A light year is the distance that light travels in one year • 9,460,730,472,580.8 km • 5,878,630,000,000 miles Parallax • Parallax- the apparent change in the position of a star in the sky. –The change is due to the change in the Earth’ position as the Earth revolves around the sun. Parallax Hertzsprung-Russell Diagram: (H-R Diagram) • It is a scatter plot • Shows the relationship between absolute brightness and surface temperature • This is the single most important diagram that astronomers use • Uses of H-R Diagram – Classify Stars – Understand how stars change over time H-R Diagram Brightest Absolute Magnitude Dimmest Hottest Surface Temp Coolest H-R Diagram H-R Diagram • Main sequence: the area where the most stars are located • Extends from the upper left corner to the lower right corner • 90% of stars are located here Life Cycle of a Star • All stars start with a NEBULA –Nebula is a large cloud of gas and dust that forms protostar with gravity • Then Nuclear Fusion occurs (atoms combine to form heavier atoms) • The star takes 2 different paths depending on their size Life Cycle of Stars Lower Mass Stars • Giant Star: outer layer expands –White Dwarf: extremely dense –Black Dwarf: dead Life Cycle of Stars • Higher Mass Stars –Super Giant: Fusion continues until iron is formed –Explosion Occurs: No more nuclear fusion • Super Nova: Star breaks apart –Neutron Star –Black Hole Death of Star • When a star begins to run out of fuel, its core shrinks and its outer portion expands –White Dwarf –Neutron Star –Black Hole Multiple Star Systems • Multi Star System: Star system with one or more companion stars –Most stars have companions but not all stars • The sun does not have a companion Multiple Star System • Example of multi star system: ALPHA CENTURI: a three star system that is the CLOSEST star to the sun. – Proxima Centuri – Alpha century A – Alpha Century B Multiple Star Systems • Binary Stars: Star systems with 2 stars • Bi = 2 (remember bicycle) • Eclipsing Binary Star System –The larger companion blocks the smaller companion Star Clusters Star Clusters:Large Groupings of Stars Open Cluster • Loose and disorganized appearance • Contain 100- 1000 stars • young stars Star Clusters Globular Cluster • more common round, densely packed stars • 100,000 to 1,000,000 • older stars Galaxies • Galaxy is a huge collection of stars bound by gravity – Contain various star groups • Billions of galaxies in the universe • 3 Types of Galaxies Spiral Galaxy Elliptical Galaxy Irregular Galaxy The Milky Way • The galaxy we live in • Spiral shaped • Looks like a milky or whitish band in the sky •Sun is located in one of the spiral arms •It has 400 billion stars Milky Way Galaxy •It takes the sun and planets over 200 million years to move around the center of the milky way Big Bang Theory • Theory is an idea that is supported by evidence • The universe began to expand with the explosion of concentrated matter and energy and has been expanding ever since