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| 1 equals average earth-sun distance=93 million miles or 150 kilometers |
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the distance light travels through space in one year 10 to the 13th km/yr |
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| nearest star other than our sun |
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| proxima centauri is 4.2 light years away |
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measuring distance to stars (indirect methods) Stellar Parallax |
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shift in apparent position caused by earth orbit (determined by photographing nearby stars against the back drop of more distant objects) |
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| stellar brightness is controlled by what 3 factors? |
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1. how large the star is
2. how hot the star is
3. how far away the star is |
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star brightness as it appears from earth with the unaided eye.
(brightest is 1st magnitude, faintest is 6th magnitude.) each goes up by 2.5x |
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apparent= -26.7
absolute=5 |
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| stars that fluctuate in brightness are known as variables |
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fluctuate due to expansion and contraction
CLASSICAL CEPHEIDS |
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| sudden brightening of a star called a nova |
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| stellar color and temperature |
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| hot stars (30000K) emit dominantly short wave radiation appear BLUE |
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| stellar color and temp. cont'd |
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| red stars (3000K) emit longer wave radiation because they are cooler. |
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| binary stars and stellar mass |
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| 18th century- astronomers discovered numerous star pairs. |
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| second star in the handle of the big dipper, is actually a double star. |
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revealed that many star pairs actually orbit each other.
United by mutual gravition
called visual binaries
50% of the stars in the universe are multiples |
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| binary star and star mass |
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Definition
| determined by the size of their orbits |
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| accumulations of gas and dust in space |
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| glow because they are close proximity to a hot blue star |
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| gaseous masses composed mostly of hydrogen |
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reflected light from nearby stars
thought to be composed of dense clouds or dust |
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not close enough to a bright star to be illuminated
appear as a dark mass or holes in the heavens |
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dark, cool, innerstellar clouds
called a protostar |
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gravitational contraction continues
-when core reaches 10 million degrees K fusion begins
-a balance between gravity (squeezing) and gas pressure (expansion) is reached and it becomes a main sequence star |
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hydrogen burning continues for a few billion years
different stars age at different rates
hot massive blue stars only last a few million years
smallest red main sequence stars may last hundreds of billions of years
average star spends 90% of it's life as a hydrogen burning main-sequence star, when hydrogen depleted star evolves rapidly and dies |
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inert helium core
all hydrogen in core is consumed
-hydrogen fusion still progressing in outer shell
-star's outer envelope is expanding
-as the star expands, it cools
-internal pressure is increasing until the star begins to consume carbon in its core
-eventually all usable nuclear fuel is consumed
-different types of stars die ar different rates |
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somewhat speculative
what we know is...
-a star, no matter what size will eventually exhaust its fuel supply
Low mass stars(<0.5*sun)
-may remain sequence for 100 billion years
-never become red giants because they do not achieve sufficient heat and pressure to fuse anything but hydrogen |
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