Astronomy Exam2
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Created by:
lealafortune on May 16, 2011
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46 terms
Terms | Definitions |
|---|---|
 Interstellar Matter Composition | Principally gas- 90% hydrogen, 9% helium, and 1% dust |
| 2 components of Interstellar dust | Extinction (dims) and reddening starlight |
| Example of interstellar dust | sunset- sun going through dust particles and turns pink and orange |
| Interstellar Extinction | Dust cloud completely blacks out light from stars behind it |
| What does Interstellar Dust look like? | about 1/10,000 mm in diameter, elongated |
| Polarization Light | Unpolarized light waves have randomly oriented electric fields |
| Why is it called an emission nebula? | Because of the brightness |
| Color region of emission nebula and cause | Reddish, caused by glowing gas |
| Color region of reflection nebula and cause | Bluish, caused by reflection of starlight from dust particles |
| Light that is scattered from dust | Reflection nebula |
| Emission Nebula | Red color comes from hydrogen formed by UV radiation from nearby stars |
| Reflection Nebula | Results when starlight is reflected from a cloud. Blue light is scattered most so it appears blue |
| Absorption Spectrum | Broad lines from star narrow lines from cloud |
| Broad Stellar Lines | Low intensity on absorption spectrum |
| Narrow Cloud Lines | Lower intensity on absorption spectrum |
| Where are 21-cm radio lines observed? | Interstellar space |
| Origin of the 21-cm line of hydrogen | The energy of the H atom is higher when the spins of the electron and the proton are parallel than when they are antiparallel -When the spins flip, microwave radiation is emitted at a wavelength of 21 cm |
| Size of molecules in space | Vary in Space from 2 to 13 atoms |
| How many atoms are required to make a star? | 10^57 |
| Interstellar Magnetic Field | Hinders contraction of a gas cloud in directions perpendicular to the magnetic field |
| Rotation | Tends to make a contracting cloud bulge in its midsection and then flatten into a disk |
| Recipe for a star | 1. dense interstellar cloud contracts and it becomes unstable and fragments 2. Trapped radiation within each fragment causes a rise in temperature 3. Under force of gravity, fragment contracts to solar-system size and density at center increases and temperature increases-called a protostar 4. After 100,000 years temperature of core reaches 1 million K and can be plotted on HR 5. Protostar shrinks 10 x sun, surface temp 4000K, core 5 mil K 6. 10 million years after its first appearance it reaches the bottom of the Hayashi track on HR diagram; central temp is 10 million K 7. After 30 million years the star's core reaches 15 mil K |
| Hayashi Track | Evolutionary track followed by a protostar during the final pre-main-sequence phase before nuclear fusion begins |
| How long does it take for 1 solar mass to occur? | 10 million years |
| Evolutionary Track | heavier elements formed by further nuclear fusion reactions in their interiors |
| Contraction Phase | Collapse under gravity |
| The time it takes to reach the main sequence depends on what? | Mass |
| Brown Dwarfs | Never become stars because they don't have enough mass to collapse properly |
| Red glow comes from what? | Hydrogen |
| Protostar | -It is the dense region at the center of the fragment -Baby stars wrapped in their blankets of dust |
| Shock Wave | Move out from the ignition of nuclear reactions in new stars to compress gas and initiate the condensation of new protostars |
| How old is Omega Centauri | 10 billion years old |
| Hydrostatic Equilibrium | Outward pressure of hot gas and inward pull of gravity -Essential to keeping the star stable throughout its main sequence lifetime |
| Hydrogen-Shell Burning | As helium as core grows, the rate of conversion of hydrogen in shell into helium increases -Helium core shrinks over weight of the star which is no longer offset by the outward pressure produced by H-burning |
| Star brightens and expands as it ascends onto which branch? | Red Giant |
| Short recipe for a red giant on the HR diagram | Its surface becomes cooler, but the star expands enormously, so it becomes brighter |
| Horizontal Branch | Where a star resides in a well-defined region of the HR diagram and where the core-helium-burning star remain for a time before resuming their journey around the HR diagram |
| Helium-Shell Burning | Shell of burning helium gas surrounding a non-burning stellar core of carbon ash |
| Red Giant Instability | Pulsations of glowing amplitude result in ejection of an envelop of stellar material and a planetary nebula is formed |
| Helium Shell Flash | Condition in which the helium-burning shell in the core of a star cannot respond to rapidly changing conditions within it, leading to a sudden temperature rise and a dramatic increase in nuclear reaction rates |
| White Dwarf | A dwarf star with sufficiently high surface temperature that is glows white |
| Observation of a white dwarf | -Low luminosity, more difficult to observe -Very hot, low luminosity |
| Stellar Roche Lobes | The tear-drop shaped lobes (zones of gravitational influence) meet at the Lagragian point |
| Close Binary Star Systems- Detached | Each within Roche lobe |
| Close Binary Star Systems- Semidetached | Star filling Roche lobe transfers matter to companion |
| Close Binary Star Systems- Contact Binary | Common Envelope |
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