what is a standard candle? alexander l. rudolph professeur invité, upmc professor of physics and...
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What is a Standard Candle?
Alexander L. RudolphProfesseur Invité, UPMC
Professor of Physics and AstronomyCalifornia State Polytechnic University,
Pomona
What is a Standard Candle?
Alexander L. RudolphProfesseur Invité, UPMC
Professor of Physics and AstronomyCalifornia State Polytechnic University,
Pomona
EUHOU Teacher Training - April 2012
Stellar LuminosityStellar Luminosity• Apparent brightness is a measure of how
bright a star appears on Earth
• Luminosity is a measure of how much energy per second (W) a star emits
• The apparent brightness of an object declines with distance (inverse square)
• If we measure apparent brightness (energy/sec/m2) and we know distance, we can get the luminosity of the star
• For Sun, apparent brightness = 1400 W/m2 and d = 150 million km = 1.5 × 1011 m
• Apparent brightness is a measure of how bright a star appears on Earth
• Luminosity is a measure of how much energy per second (W) a star emits
• The apparent brightness of an object declines with distance (inverse square)
• If we measure apparent brightness (energy/sec/m2) and we know distance, we can get the luminosity of the star
• For Sun, apparent brightness = 1400 W/m2 and d = 150 million km = 1.5 × 1011 m
Brightness Quiz IBrightness Quiz I
Two identical 50 W bulbs are placed at different distances
from you. Which one appears brighter?
A. The closer one
B. The further one
C. They appear the same brightness
D. There is not enough information to tell
Two identical 50 W bulbs are placed at different distances
from you. Which one appears brighter?
A. The closer one
B. The further one
C. They appear the same brightness
D. There is not enough information to tell
EUHOU Teacher Training - April 2012
Brightness Quiz IIBrightness Quiz II
A 50 W and a 100 W bulb are placed the same distancefrom you. Which one appears brighter?
A. The 50 W bulb
B. The 100 W bulb
C. They appear the same brightness
D. There is not enough information to tell
A 50 W and a 100 W bulb are placed the same distancefrom you. Which one appears brighter?
A. The 50 W bulb
B. The 100 W bulb
C. They appear the same brightness
D. There is not enough information to tell
EUHOU Teacher Training - April 2012
Brightness Quiz IIIBrightness Quiz III
A 50 W and a 100 W bulb are placed at different distances
from you. If the 100 W bulb is closer, which one appears
brighter?
A. The 50 W bulb
B. The 100 W bulb
C. They appear the same brightness
D. There is not enough information to tell
A 50 W and a 100 W bulb are placed at different distances
from you. If the 100 W bulb is closer, which one appears
brighter?
A. The 50 W bulb
B. The 100 W bulb
C. They appear the same brightness
D. There is not enough information to tell
EUHOU Teacher Training - April 2012
Brightness Quiz IVBrightness Quiz IV
A 50 W and a 100 W bulb are placed at different distances
from you. If the 50 W bulb is closer, which one appears brighter?
A. The 50 W bulb
B. The 100 W bulb
C. They appear the same brightness
D. There is not enough information to tell
A 50 W and a 100 W bulb are placed at different distances
from you. If the 50 W bulb is closer, which one appears brighter?
A. The 50 W bulb
B. The 100 W bulb
C. They appear the same brightness
D. There is not enough information to tell
EUHOU Teacher Training - April 2012
Brightness Quiz VBrightness Quiz VTwo identical stars, one 5 light years from Earth, and a second 50 light years from Earth are discovered. How
much fainter does the farther star appear to be?
A. square root of 10
B. 10
C. 100
D. 1,000
E. the farther star does not appear fainter, since it is identical
Two identical stars, one 5 light years from Earth, and a second 50 light years from Earth are discovered. How
much fainter does the farther star appear to be?
A. square root of 10
B. 10
C. 100
D. 1,000
E. the farther star does not appear fainter, since it is identical
EUHOU Teacher Training - April 2012
Standard Candles Standard Candles
• We can use this equation to find the distances to objects in the universe using the concept of a standard candle
• Thus, if we know an object’s luminosity, and measure its apparent brightness, we can find its distance
• We can use this equation to find the distances to objects in the universe using the concept of a standard candle
• Thus, if we know an object’s luminosity, and measure its apparent brightness, we can find its distance
EUHOU Teacher Training - April 2012
• Cepheid variable stars (Inter. Fig. II)• Very bright stars which vary in
luminosity in a regular way• A relation exists between variation
period and the star’s luminosity• Calibrated using nearby Cepheids
of known distance
• White Dwarf (Type I) supernovae• All WD Sne cross the
Chandrasekhar limit and explode in the same way; hence all have similar luminosities
• Calibrated in nearby galaxies of known distance
• Cepheid variable stars (Inter. Fig. II)• Very bright stars which vary in
luminosity in a regular way• A relation exists between variation
period and the star’s luminosity• Calibrated using nearby Cepheids
of known distance
• White Dwarf (Type I) supernovae• All WD Sne cross the
Chandrasekhar limit and explode in the same way; hence all have similar luminosities
• Calibrated in nearby galaxies of known distance
Standard Candles - Examples Standard Candles - Examples
EUHOU Teacher Training - April 2012
Galactic Distances QuizGalactic Distances Quiz
Cepheid variable stars are located in two different galaxies, A and B.
Both stars have the same average apparent brightness. The star in galaxy A has a bright-dim-bright period of 10 days, while the one in galaxy B has a bright-dim-bright period of 30 days. Which of the
two galaxies is at a greater distance from us?
a) Galaxy Ab) Galaxy Bc) They are located at the
same distance.d) There is insufficient
information to tell.
Cepheid variable stars are located in two different galaxies, A and B.
Both stars have the same average apparent brightness. The star in galaxy A has a bright-dim-bright period of 10 days, while the one in galaxy B has a bright-dim-bright period of 30 days. Which of the
two galaxies is at a greater distance from us?
a) Galaxy Ab) Galaxy Bc) They are located at the
same distance.d) There is insufficient
information to tell.
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