Term
| What is the composition of a star's mass at birth? |
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Definition
3/4 hydrogen
1/4 helium
2% heavy elements |
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Term
| apparent brightness (flux) |
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Definition
How bright a star looks in the sky from earth. This does not take star distance into account.
amount of power (energy/sec) reaching us per unit area |
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Term
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Definition
| total amount of power (energy/ sec) a star radiates into space |
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Term
| What is the difference between luminosity and apparent brightness? |
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Definition
| Luminosity is a measure of power and apparent brightness is a measure of power per unit area |
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Term
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Definition
| This is the distance squared. If we viewed our Sun at twice the distance we are now the formula would be (2^2 =4). Therefore, the Sun would look 4 times as dim as it does now. This is the same for any distance. i.e. 10 times the distance would be 10^2=100 times less bright |
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Term
| Inverse Square Law for Light |
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Definition
apparent brightness
=
luminosity/ 4pi x distance^2
(in watts) |
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Term
| Complications of the Inverse Square Law for light |
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Definition
difficulty measuring apparent brightness (can only measure part of the spectrum)
Law only works if the light does not get disrupted by anything. Most light goes through some clouds |
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Term
| total luminosity and total apparent brightness |
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Definition
| describes the measurements we would have if we were able to detect photons across the entire electromagnetic spectrum |
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Term
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Definition
Small shifts in the star's position caused by Earth's movement around the sun
More distant star's have smaller parallax angles |
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Term
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Definition
All star's have parallax angles of less than one arcsecond
ancient astronomers were not able to see the movement with the naked eye and even today's telescopes cannot measure the furthest stars (few hundred light years - local solar neighborhood) |
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Term
| Calculate distance of stars in parsecs |
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Definition
| d (in parsecs) = 1/ p (in arcsecs) |
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Term
| 1 parsec is equivalent to _____ in light years |
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Definition
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Term
| distance to stars in light years (formula) |
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Definition
d (in light years)
=
3.26 * (1/p (in arcseconds) |
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Term
| Characteristics of Luminosity |
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Definition
there is a wide range of luminosity with the sun in the middle. The lowest is 10^-4Lsun and the highest 10^6Lsun
there are more dim luminosity stars than high luminosity stars |
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Term
| magnitude system of stellar classification |
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Definition
| the smaller the number, the more bright the star (i.e. 1 would be the brightest) |
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Term
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Definition
| the luminosity a star would have if the star were 20 parsecs from Earth |
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Term
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Definition
| Determined either from the star's color or from the spectrum it emits |
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Term
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Definition
| Astronomers calculate the amount of blue and red light a star is emitting to determine surface temperature |
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Term
| Spectral Type and Temperature |
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Definition
More accurate than determining temperature through color which is disrupted by interstellar dust. Each star is assigned a letter
OBAFGKM!
O has the hottest stars (40,000K)
M has the coolest stars (3,000K)
within these classifications, the larger the number the cooler the star (i.e. M9 is cooler than M1)
Based on Balmer Lines |
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Term
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Definition
| At high temperatures, Hydrogen becomes ionized and can only emit very weak spectral lines, but at low temperatures the lines are strong. (i.e. O type stars have weak Hydrogen Spectral Lines) |
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Term
| How do we measure the masses of stars? |
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Definition
| Newton's Version of Kepler's Third Law. This can only be done in binary systems |
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Term
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Definition
Visual System - can be observed
Eclipsing System - one star eclipses the other and the luminosity fluctuates
Spectroscopic - blue shifts (comes towards us) and red shifts (moving away) as a result of motion
in order to measure star mass, you must measure the shift of the stars relative to each other. Eclipsing systems are especially important parts of measurement since they are the most accurate and easiest to measure. |
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Term
| Hertzsprung-Russell diagram |
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Definition
| Plot star luminosity and spectral type. Stars in the upper left are hot and luminous and stars in the upper right are cool and luminous etc. |
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Term
| What do H-R diagrams tell us about stellar radii? |
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Definition
| smaller stars are in the lower left-hand corner and bigger stars are in the upper right |
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Term
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Definition
| designates the size of stars on the H-R diagram (i.e. Supergiants are I and main-sequence are V) |
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Term
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Definition
the majority of the stars in the galaxy are main sequence.
they fuse hydrogen and helium in their cores
Their masses matter because that determines the balancing act |
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Term
| are low mass or high mass stars more common |
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Definition
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Term
| Which has a longer life-time, low-mass or high mass stars? |
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Definition
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Term
| How are surface temperature and mass related |
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Definition
| The higher the surface temperature, the higher the mass. |
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Term
| How can you tell the age of a globular cluster? |
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Definition
| Must look at the age of the turn-off point. The age of the turn-off point is the age of the cluster |
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