What are the properties of Stars? 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): the energy 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 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 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

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? Which star is brightest?

Which star looks brightest from Earth? Sun 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? Sun Which 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 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!

H-R Diagram Interpretation Graphing Activity

Absolute Magnitude _ Spectral Type -10 -5 5 10 15 0 1 2 3 4 5 6 7 8 9 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