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ASTR 101: EXAM 2
What produces a continuous spectrum |
a solid, liquid, or dense gas excited to emit light will radiate at all
wavelengths |
what produces an emission line spectrum |
a low-density gas excited to emit light will do so at specific wavelengths |
what produces an absorption spectrum |
if light comprising a continuous spectrum passes through a cool, low density gas |
terrestrial planets |
Mercury, Venus, Earth, Mars.
-rocky. relatively thin atmospheres. some live volcanoes or evidence of past lava flows. few moons |
Jovian planets |
Jupiter, Saturn, Uranus, Neptune
-gas giants. low average density compared to terrestrial. all have rings. all have many moons |
the carbon dioxide cycle |
this cycle acts a thermostat for the Earth, because the rate at which carbon dioxide is extracted from the atmosphere is very sensitive to temperature. a small change in the earth’s atmosphere can be offset by a change in the carbon dioxide cycle |
principal greenhouse gases |
CO2 : carbon dioxide
CH4 : methane
N2O : nitrous oxide
H2O : water vapor |
what is a comet nucleus made of |
rocks and gravel frozen together with ice |
what is a comet tail made of |
ice boils off, leaving gas + dust tail |
what are meteors |
piece sof sand that vaporizes in earths atmosphere due to friction |
what is the titus-bode law |
rough rule that predicts the spacing of the planets in the solar system. lead Bode to predict the asteroid belt situated between Mars and Jupiter |
what is dwarf planet |
doesn't meet rules for planet
orbits a star
be large enough to be round
clear out most objects form your orbital path |
destructive power of a collision with an asteroid or comet nucleus comes from the kinetic energy of the object hitting the earth |
kinetic energy is ½ mv2 so it increase rapidly with the velocity of the impact |
what are the three most abundant elements in the earths crust |
oxygen, silicon, aluminum |
what is the Kuiper belt |
extends from the orbit of Neptune (30 AU) out to roughly 55 AU. It consists of many KM-sized objects and a number of dwarf planets. there might be 70,000 Kuiper belt objects. the Kuiper belt is the repository of long period comets, those with periods > 200 years. |
what is an extra-solar planet |
planets orbiting other stars |
what are the 3 principal ways of discovering extra-solar planets |
periodic variations n the radial velocity of a star
transits of a large planet in front of a star- you measure a decrease in the light of the star
direct imaging |
how many extra-solar planets have we discovered so far |
694 |
photosphere |
suns atmosphere
pale yellow layer of the sun that we see every day. T ~ 5800 °K |
chromosphere |
suns atmosphere
above photosphere. see colored loops of gas there during a total
solar eclipse. ~4500 < x < 10000 °K |
corona |
suns atmosphere
hottest region. lowest density. observe during total solar eclipse |
the nature of neutrinos that come from the sun |
hydrogen fusion emits neutrinos
-neutrino: light atomic particle with no charge
-very weak interactions with matter
-should escape the core freely |
how do we know that sunspots are cooler than the rest of the photosphere |
it is a contrast effect. the temp is lower and a cooler black body gives off less light |
magnetic fields in the sun |
-produce sunspots
-polarity of sun spots reverses every 11 years |
cause of the aurora borealis/australis in the Earth’s atmosphere |
when sun sis experiencing a solar maximum. lots of spots, strong magnetic storms, strong solar wind. when wind hits Earth’s atmosphere, radio transmission is disrupted. observed as northern lights. |
relationship between parallax of stars and the distances
|
d(pc) = 1/ac
-greater the parallax, smaller the distance
|
what is a parsec |
“parallax of one second of arc”. 3.26 light years.
reciprocal of parallax in arcsec |
what are stellar radial velocities?
|
measured from the Doppler shift of the lines in a stars spectrum |
what are proper motions |
number of arc seconds/year that a star moves with respect to the
distance background of stars or galaxies |
inverse square law of light intensity |
allows us to calculate the stars luminosity if we know its distance or calculate distance if we know its luminosity
|
what do we mean by the absolute magnitude of a star |
apparent magnitude a star would have it d=10pc |
what does this mean? Mv = mv + 5 – 5 log d? (the apparent magnitudes have to be corrected for any effects of interstellar dimming due to dust. otherwise your distances aren’t right) |
Mv: absolute apparent magnitude
mv: apparent visual magnitude correct for any dimming by interstellar dust
d: distance in parsec |
Hertzsprung-Russell Diagram: what is a plot of |
plot of intrinsic luminosities vs. photospheric temperatures. |
Hertzsprung-Russell Diagram: what is the range of photospheric temperatures |
range of photospheric temperatures: 3000-30000 °K |
Hertzsprung-Russell Diagram: what is the range of luminosities |
range of intrinsic luminosities: 10-4-106 |
Hertzsprung-Russell Diagram: what is the range of masses of main sequence stars |
range of mass of main sequence stars: 0.08 to 60-100 solar masses |
what does this mean: TMS is proportional to M-2.5 |
the lifetime of a main sequence star |
how can we get observational confirmation from star clusters concerning the main sequence lifetimes of stars? |
-all stars in a cluster lie at about the same distance from earth
-all stars in the cluster were formed at about the same time (w/in a few mil. years) |
spectroscopic binaries |
revealed by the Doppler stars of the 2 stars in a close binary system |
eclipsing binaries |
revealed by mutual eclipses of 2 stars. the observer must be close to the
plane of the orbit of the 2 stars |
how does interstellar dust affect the light of stars along the line of sight |
dimming, reddening, star counts |
what fraction (by mass) of the interstellar medium is in gas and what fraction is dust |
~1% is dust
99% is gas |
how long is the collapse from interstellar dust |
5 million years |
how long is the protostar |
30 million years |
how long is the main sequence phase |
10 billion years |
how long is the giant phase |
about 1 billion years |
how long is the planetary nebula |
50000 years |
how long is the white dwarf star |
forever |
What is the CNO cycle? it is the principal energy generation mechanism for which kind of stars |
faster chain of hydrogen fusion because reactions also occur with carbon, nitrogen,
and oxygen
1.1+ solar mass stars (high mass stars) |
what is the minimum temperature to run the proton-proton cycle in a stars core |
10 million K |
why are Cepheid’s importanT |
imbalance between pressure of stars layers and energy transport. causes
star to pulsate (periods of days) |
why are RR lyrae stars important |
found in globular clusters. about 30 times brighter than the sun (periods
of hours) |
what is the period-luminosity relation? |
relation between the pulsation period and absolute
brightness |
relation between the pulsation period and absolute
brightness |
runs out of fuel -> collapses -> turns into a supernova -> neutron star/black hole |
what is degenerate electron matter
|
as the Hydrogen is converted to Helium in the core, the gas becomes denser as the energy levels are filled |
what is the maximum mass of a white dwarf star |
1.4 solar masses (Chandrasekhar’s limit) |
what does fully convective mean |
the gas in the outer layers of stars mixes down into the core
completely |
stars less than 0.4 solar masses are fully convective. how long do they last as main sequence stars? |
10 billion years |
how long do they last as main sequence stars? do they become giant stars? |
NO |
how is a stars evolution changed if it has a really close companion |
higher mass star evolves first. expands until it loses material due to other stars gravitational pull. material flows to smaller star & becomes a white dwarf. when second star is giant enough to dump a material to the white dwarf, H collects on white dwarf and star gets temporarily brighter. if it is dumped over limit, it explodes as Type 1a supernovae and nothing is left behind. |
what is the structure of a 10 solar mass star prior to its explosion as a type 1 supernova |
iron tightly bound nucleus. nuclear reactions cause outer layers to squeeze down causing it to explode as type 2 supernovae |
what do we mean by the term standard candle? what good are they? |
an object whose brightness at some time (or mean brightness) is known an can be used to determine astronomical distances |
what are type 1a supernovae better standard candles for galaxies more than 25 megaparsecs distant (compared to say, Cepheid’s) |
ype 1a supernovae are 4 billion times brighter than Cepheids. thus hey can see much farther than Cepheids
|
what are the mean densities of the sun, a typical white dwarf star, a neutron star |
sun: 1.4g/cm3
white dwarf: several tons/teaspoon
neutron star: 1015 g/cm3 |
how massive is the black hole in the center of our galaxy |
2.6 0.2 million times the mass of the sun |