ch. 28 the stars properties of stars ??? are all stars the same? what’s different about them? list...
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Ch. 28 The Stars
Properties of Stars ???
Are all stars the same?What’s different about them?
List a few differences….
Luminosity- Brightness
• 3 factors control brightness of a star:– How big (size) it is– How hot (temperature)it is– How far away (distance)it is
Apparent Magnitude• Hipparchus, 2nd century B.C.• Classified all the 1000 stars visible to the
naked eye on a scale of 1 to 6.• 1 = brightest• Relative: ranking of brightness• Brightness or a star as it appears when
viewed from Earth
Absolute Magnitude
• The “true” brightness (LUMINOSITY)• Measurable: the amount of energy/sec• Distance: if the stars were the same distance
from Earth. (32.6 ly or 10 pc)
Star brightness scale
The magnitude scale is logarithmic: a change in 5 magnitudes = change of 100x’s the brightness
Binary (double) Stars
Rigel A and Rigel B in the constellation Orion
Binary stars in the constellation Scorpio
Most stars are binary (two stars rotating around each other due to gravitational attraction) or multiple systems.
Parallax to measure distances of stars
Measured in PARSECs For very distance stars, the parallax is so small, it is very difficult to measure
Sirius is the brightest star in the sky at 2.6 pc distance.
Pollux (10 pc) and Rigel (240 pc) appear to have similar brightness,Yet Rigel is 24 x’s FARTHER DISTANCE away! How can that be?
Pollux
Rigel
Alpha Centauri (triple star system)Has the largest stellar parallax270,000 AU or 4.3 light-years300,000 times distance from Earth to Sun!
http://www.youtube.com/watch?v=vg3noqtm0L0&safety_mode=true&persist_safety_mode=1 Sheldon star steps
Our stellar neighborhoodNearest stars to our Sun
Distance to our Nearest Neighbor
1. Proxima Centauri is the closest– It has the largest stellar parallax 1.3 pc Parsecs or parallax second
• 19 trillion miles
– 270,000 AU, astronomical units • distance from Earth to Sun or 93 million miles
– 4.3 ly light-year • (distance light travels in a year: 6 trillion miles!
Mass of Stars• Calculated indirectly, using its
gravitaitonal affect on nearby objects (Newton’s law of gravity)
• Measured in ‘solar masses’• Other stars are compared to
our Sun’s mass: 1 SM
• Can be up to 2000 SM !!
Stellar Size
• If the star is close enough, we can measure the size by parallax.
• If we know a stars luminosity, and temperature,• Scientists can indirectly determine the radius
(size) of a star.• Compared to our Sun’s radius: 1R
AldebaranCool temp. = 4000 KLow luminosity = 2.3 x 1025 WIts COOL and DIMSo…. for us to see it, Its size must be…..
Procyon BHigh temp. = 8500KLarge luminosity = 1.3 x 1029 WIts HOT and BRIGHTYet it’s not the brightest star,So its size must be….BIG!! 40 R
Sun radiusSmall .01 R
Sun’s CompositionWhat is the sun made of and how do scientists
know??????
Spectral AnalysisOf the light from the photosphere
ENERGY FROM THE SUN
http://www.classzone.com/books/earth_science/terc/content/visualizations/es2601/es2601page01.cfm?chapter_no=26
Electromagnetic Spectrum and Wavelength
Suns’ Spectra
Each element has its own spectra that can be used to identify the element
Hydrogen
Combined, what COLOR does the Sun appear to us?
Helium
Our Sun is yellow and has a surface temp. of 6000K
Every element has a unique spectra that can be used to identify it.
Temperature = Color
H-R diagram graph
30,000
Color
(RED)blue yellow
Tem
pera
ture
ºC
0
Rigel
Sirius
Sun
Hertzsprung-Russell Diagram (pg.663)Lu
min
osity
/ a
bsol
ute
brig
htne
ss
dim
bright
1-
Surface temperature / color Cooler (RED)Hotter /blue3000 K30,000 K
Cool and bright = red giant
Hot and dim = blue dwarf
Astronomers classify stars in spectral classes by color/temperature
3000°
The Hertzsprung-Russell diagram isn’t just an orginazational chart for the the stars, but the life cycle of the stars!
H-R diagram is the Life Cycle of the stars!