Stars and Galaxies

Chapter 27—Stars and Galaxies

What is a Star? Star: A body of gas that gives off a tremendous amount of radiant energy in the form of light and heat

What is Light? ,[object Object],[object Object]

[object Object],[object Object],[object Object]

Big Bang Theory ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Evidence supporting Big Bang Theory… ,[object Object],[object Object],[object Object]

And Evidence from the Doppler Effect ,[object Object],[object Object]

Light and the Universe ,[object Object],[object Object],[object Object],[object Object]

Parallax ,[object Object],[object Object],[object Object],[object Object]

Why Do Stars Twinkle?? ,[object Object],[object Object],[object Object],[object Object]

Characteristics of Stars Size: anywhere from 20km to 1 trillion km in diameter Mass: the amount of matter Color: stars can be red, blue, white, orange or yellow Composition: contain different elements determined using spectra

Characteristics of Stars Temperature: Blue is the hottest (35000 ° C) Red is the coolest (3000 ° C) Yellow (our sun) (5500°C)

Luminosity —the actual brightness of a star ,[object Object],Apparent Magnitude —A measure of how bright a star appears to be on earth ,[object Object],[object Object],Absolute Magnitude —A measure of how bright a star would be if all Stars were at the same distance—ten parsecs—from Earth

0 -10 -20 -30 10 20 30 Magnitudes Dimmer Brighter Our Sun Sirius Brightest in the sky from Earth Polaris/North Star -26.5 -2 3 6 We can not see dimmer than +6 with naked eye

Star 1 High luminosity Far from earth = lower apparent magnitude Star 2 Low luminosity Close to earth = higher apparent magnitude Apparent Magnitude v. Luminosity

Hertzsprung-Russel Diagram ,[object Object],Spectral Class —designates the color of stars >depends on temperature >Hottest to the coolest >Blue to White to yellow to orange to Red

Kinds of Stars super giants- largest of all stars, very luminous red giants- cooler, large, very luminous dwarf stars- less luminous, red, orange or yellow white dwarf- very faint, small and dense

Variable Stars- vary in brightness over regular periods or cycles 2 types: A. pulsating change in brightness as they contract (brighter) Or expand (dimmer) Example: cepheid - yellow supergiant

B. nonpulsating Eclipsing Binary 2 stars of unequal brightness that revolve around each other brightness depends on which one is in front of the other

Pulsars star that releases light and radio waves in pulses may be the neutron star formed in a supernova it looks like it pulses because it is rotating , like a searchlight

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Stellar Masses ,[object Object],[object Object],[object Object]

Life Stages of Stars With Solar Masses less than 8 Solar Masses

Main Sequence Star (Our Sun) — >90% of all stars >The star is stable >Burns Hydrogen gas to Helium in its core through nuclear fusion > The energy released causes the star to shine. >Stars spend about 90% of their active lifetime as main sequence stars. Red Giant — >The star begins to run out of fuel and the core begins to shrink >Helium turns into Carbon >Rapid burning of helium causes outer layer to puff out, cooling the star >The star turns red

Planetary Nebula — >Outer layers are ejected as core continues to shrink >Shell of hot gas >Core is exposed White Dwarf — >Low mass core continues to shrink creating a white dwarf >Surrounded by the Planetary Nebula

Stars Evolution Greater than 8 Solar Masses ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Star Systems ,[object Object],[object Object],[object Object]

Novas & Supernovas ,[object Object],[object Object],[object Object]

Star Clusters ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Other Galaxies ,[object Object],[object Object],[object Object],[object Object]

Nebulae ,[object Object],[object Object],[object Object],Stellar nursery is a nebula ( a large cloud of hydrogen gas in space) in which star formation is occurring

Galaxies ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Constellations ,[object Object],[object Object],[object Object],[object Object]

Quasars ,[object Object],[object Object]

[object Object],[object Object],[object Object],[object Object],Constellation of Orion is seen during winter

Stars and Galaxies

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