250 likes | 280 Views
Chapter 12 Measuring the Stars What are the properties of Stars? What are the patterns among Stars?. From the Sun we’ve learned : stars are far away stars are bright stars are hot stars are massive. How FAR AWAY? ( DISTANCE ) How BRIGHT? ( LUMINOSITY )
E N D
Chapter 12 Measuring the Stars What are the properties of Stars? What are the patterns among Stars?
From the Sun we’ve learned: • stars are far away • stars are bright • stars are hot • stars are massive • How FAR AWAY? (DISTANCE) • How BRIGHT? (LUMINOSITY) • How HOT? (SPECTRAL TYPE) • How MASSIVE? (MASS)
Stellar Brightness -- what is it? The brightness of an object depends on both distance and energy output
Amount of energy output a star radiates is called the Luminosity (L): theenergy per second Amount of starlight that reaches Earth is called the Apparent brightness (m)
Two Kinds of Brightness • Apparent Magnitude (m):How bright the object appears to us on Earth. • Absolute Magnitude (M):How bright a star actually is, its intrinsic brightness
Two Kinds of Brightness • Apparent Magnitude:How bright the object appears to us on Earth.
Two Kinds of Brightness • Apparent Magnitude:How bright the object appears to us on Earth. • Which would look brighter? Vega, m = 0.03 Antares, m = 1.06 • Which would look brighter? Sirius, m = -1.4 Venus, m = -4.4
Two Kinds of Brightness • Apparent Magnitude:How bright the object appears to us on Earth. • Which would look brighter? Vega, m = 0.03 Antares, m = 1.06 • Which would look brighter? Sirius, m = -1.4 Venus, m = -4.4
Two Kinds of Brightness • Absolute Magnitude:How bright a star actually is, its intrinsic brightness PROBLEM:stars are at different distances from Earth and so it’s hard to know which stars are ACTUALLY brighter versus which APPEAR bright
Compare some stars: Absolute Apparent MSun = 4.8 mSun = -26 MSirius = 1.4 mSirius = -1.46 MBetelgeuse = -5.6 mBetelgeuse = 0.50 Which star looks brightest from Earth?Which star is brightest?
Compare some stars: Absolute Apparent MSun = 4.8 mSun = -26 MSirius = 1.4 mSirius = -1.46 MBetelgeuse = -5.6 mBetelgeuse = 0.50 Which star looks brightest from Earth?SunWhich star is brightest? Betelgeuse
Summary of Spectral Classes Keep in mind this classification is for the star’s SURFACE, only!!!!!
General properties of Stars • Brightness • Temperature • Mass Is there a way we can use the general properties of stars to get a “snap shot” about the stars????
THE H-R DIAGRAM • Enjar Hertzsprung and Henry Norris Russell • graph of luminosity (absolute magnitude) vs temperature (spectral class)
Herzsprung Russell Diagram H-R diagram plots the luminosity and temperature of stars Luminosity brightness temperature
brightness temperature
Luminosity brightness temperature
Mass - Luminosity Relation Luminosity brightness mass
Most stars fall somewhere on the main-sequence of the H-R diagram Main-sequence stars are fusing hydrogen into helium in their cores like the Sun Luminous main-sequence stars are hot (blue) Less luminous ones are cooler (yellow or red) Main Sequence
Mass measurements of main-sequence stars show that the hot, blue stars are much more massive than the cool, red ones High-mass stars Short lived stars Low-mass stars Long lived stars
End of Chapter 12 Now you know the basics of star measurements!
-10 -5 Absolute Magnitude 0 5 10 _ 15 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 Spectral Type