Astronomy Test 2
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How big is the total mass in the asteroild belt?
10% the Lunar Mass
What is the source of some additional comets?
The Kuniper Belt
Planets going around other things than the Sun
Describe the Theory of star formation.
- Raw material in Interstellar clouds
- Cloud collisions cause compression
- Gravitational collapse
- Faster rotation leads to flattening of outer region into disk
Describe the Theory of Planet formation.
- Accretion- rear end collisions increase dust grain size
- Larger grains grow faster
- Result: A planet with leftover debris
What are some Planet discovery techniques?
- Doppler Shift of star's "wobble"
- Transits of planet across star
- Selection effects
Describe the Stellar Interior Models.
- Interior cannot be observed directly
- Models start with specified mass and chemical composition
- Calculate resultion surface temp., luminosity, and radius
Name the 5 physical principles.
1. pressure v.s. gravity balance
Io, despite its relatiely small size, has a crust which erupts with sulfur-rich lava and geysers. Why?
This moon is flexed by tidal forces from Jupiter and Europa
Descending below Jupiter's clouds and deep into its atmosphere, we would enter into what kind of region?
An ocean of liquid hydrogen
In the balance between pressure and gravity in a star, what must the pressure do?
Push outward with a force equal to the weight of the overlying layers
What property of the Sun is numerically smaller than the corresponding value for the Earth?
In the second step of the fundamental nuclear reactions in the Sun, what is produced when a deuterium nucleus and a proton fuse?
A helium isotope and a gamma ray
EInstein's equation for the conversion of mass into energy involves what fundamental constant?
The vacuum speed of light
Why are high temperatures required for nuclear fusion reactions?
To overcome the electrical repulsion of the nuclei
Approximate planetary spacing regularity which matches Uranus and the asteroid belu
What are the surface layers of comets heated by?
Sunlight releasing gases and solid grains into coma
Describe the tail of a comet.
- Points away from the sun
- Ionized gas portion pushed by solar wind
- Dust grain portion by radiation pressure of reflected sunlight
What is the discovery of the periodicity of Halley's Comet supported by?
The application of Kepler's Laws to things other than planets
Asteroid fragments and comet debris with the potential to collide with earth
The glowing trail of atmospheric gases, heated by the passage of a meteroid
The pieces which survive atmospheric friction and hit the earth's surface
When do meteor showers occur?
When the earth crosses the orbit of a decaying comet
Why are there no meteorite showers?
COmet debris generally do not survive the atmospheric friction
What are some characteristics of Planetary orbits?
- common plane and direction
- low eccentricity
- rotation shows similar order
- moons have similar motions
What do Terrestrial and Jovian planets have in common?
size and composition
Describe the Solar System origin.
- collapse of an interstellar cloud
- cloud contracts, rotates faster, outer parts flatten into a disk
- as disk cools, solid grains form, forming planets
What causes the annual parallax shift?
the earth's orbital motion (inversely proportional to distance)
Other than parallax, how else can you observe stars?
Apparent brighness of stars (brightness fades B~1/d2)
A measure of the Doppler Shift, tells the the larger the shift, the higher the velocity (works at any distance)
Requires both the angular rate of change and the distance (works only for nearby stars)
Describe the solar motion of Vega.
About 20 km/s toward Vega-ewuivalent to 4 AU/yr
What is the goal of stellar luminosity?
To measure energy recieved and then allow for the distance to get the total power emitted
How is the energy recieved from luminosity measured?
on the apparent magnitude scale; 1-brightest--6-faintest
Describe the HR Diagram.
- Vertical axis- Luminosity
- Horizontal axis- Temperature (backwards)
- main sequence, giants, supergiants, whitedwarfs
- star sequence from high-low temp. O B A F G K M
- Lower main sequence stars are most common
How can the radius of some nearby large stars be found?
direct measurement of angular size and distance
The unresolved systems seen "edge on"; the time required for it determines the relative sizes of the two stars
If _____ and _____ are known, a good radius estimate can be calculated
luminosity and temperature
Describe the stars range in the HR Diagram.
- Main Sequence-0.1-10x Sun
- Giants/Supergiants- 100x Solar
- White Dwarfs- only 1/100 sun's size=earth's radius
Those where both star images are resolved; measured by seperation and period
Unresolved systems with a spectrum that shows two sets of oppositely Doppler shifted spectral lines
Describe the masses of Binary stars.
- most masses range from .07 to 100 times the sun
- Lower end of range set by core temperature required for nuclear power source
- upper end set by short lifetime and instability
Describe the range of temperatures and densities of Interstellar matter.
- cold and dense with H2 molecules
- hot and thin with H+ ions
What is the evidence of interstellar gas?
- emission nebulae
- interstellar absorption lines
- radiowavelength spectral lines (espically at 21-cm from H)
What is the evidence for interstellar dust?
- dark nebulae
- reflection nebulae
- interstellar reddening
- infared emission
What conditions are needed for new stars?
Cold, massive, dense, molecular clouds
How much of the gravitational energy release is retained to heal the prostar?
More massive stars take less time; low mass stars take longer; at a core temperature of 10 million K, what happens?
Fusion begins and the star readjusts to a stable "main sequence" state
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