question

why are extrasolar planets hard to detect directly?

answer

1. planets are extremely tiny compared to the vast distances between stars 2. stars are typically a billion times brighter than the light reflected by any orbiting planet, so starlight tends to overwhelm any planetary light in photographs

question

how can gravitational tugs from orbiting planets affect the motion of a star?

answer

The planets cause the star to wobble around on the point of the system's center of mass

question

summarize the planetary properties we can measure w current detection methods

answer

orbital period, orbital distance, eccentricity, mass, size, density, temperature

question

what 2 forces are balanced in gravitational equilibrium? what does it mean for the sun to be energy balanced?

answer

the outward push of internal gas pressure ; inward pull of gravity; it means that the rate @ which fusion releases energy in the sun's core & the rate @ which the sun's surface radiates this energy into space are equal

question

why does nuclear fusion require high temps and pressures?

answer

the high temp is important bc the nuclei must collide @ very high speeds if they are to come close enough to fuse

question

describe how a natural solar thermostat keeps the core fusion rate steady in the sun

answer

a slight rise in core temp leads to a large increase in the fusion rate that raises the core pressure causing the core to expand ; cool down

question

how do mathematical models help us learn about conditions inside the sun? what gives us confidence in those models?

answer

w a computer ; the model we can calculate the sun's temp, pressure & density @ any depth

question

explain how we can learn about the lives of stars

answer

telescopes????

question

how is a stars apparent brightness related to its luminosity?

answer

apparent brightness is the amount of power reaching us per unit area & luminosity is the total amount of power that a star emits into space

question

how do we use stellar parallax to determine a star's distance ; how can we then determine its luminosity?

answer

Astronomers can measure parallax by measuring the position of a nearby star very carefully with respect to more distant stars behind it, then measuring those distances again six months later when the Earth is on the opposite side of its orbit. The shift is less than an arcsecond even for the nearest star. It was not until telescopes were invented that astronomers could measure parallaxes at all accurately.

question

what is the defining characteristic of a main-sequence star? explain why more massive main-sequence stars are more luminous ; have hotter surfaces than less massive main-sequence stars

answer

main-sequence stars have hot surfaces; mass determines the balancing point @ which the energy released by H fusion in the core=the energy lost from the star's surface

question

which stars have longer lifetimes

answer

less massive stars

question

how do giants & supergiants differ from main-sequence stars?

answer

they are cool & red, emit less light per unit surface, enormous; they are nearing the end of their lives; betelgeuse is a supergiant

question

why is a star's birth mass its most fundamental property?

answer

A star's birth mass is the most important predictor of a star's lifetime. A star born with high mass will have a short lifespan; a star born with low mass will have a significantly longer lifespan

question

describe in general terms how open clusters ; globular clusters differ in their number of stars, ages, ; locations in a galaxy

answer

-globular clusters are densely packed, found in the halo of a galaxy, and are older -open clusters are moderately sized, found in the disk of a galaxy, and are young in age

question

why do H-R diagrams look different for star clusters of different ages? how does the location of the main-sequence turnoff point tell us the age of the star cluster?

answer

-clusters at different ages have different turnoff points -age of the cluster is equal to the lifetimes of stars at the main sequence turnoff point

question

molecular cloud

answer

cool clouds in which stars form

question

what is degeneracy pressure?

answer

a type of pressure unrelated to an object's temp, which arises when electrons or neutrons are packed so tightly that the exclusion & uncertainty principles come into play

question

what is thermal pressure?

answer

the ordinary pressure in a gas arising from motions of particles that can be attributed to the object's temp

question

briefly describe the sun's life stages after it exhausts its core hydrogen. discuss the changes in the sun's core ; the changes visible from outside the sun

answer

At the moment our Sun is in the main sequence stage. Stars like our sun spend 90% of their life shining steadily as main sequence stars. After the sun has run out of hydrogen in its core, nuclear fusion will stop. The sun's core will begin to shrink, but the sun's outer layer will expand outwards. After 1 billion years of the sun's expansion, its size and Luminosity will allow it to become a red giant. Eventually, it will be hot enough that helium particles will be able to fuse together. The rising density and temperature will have the sun eject its outer layers into space as a planetary nebula, leaving it exposed core as a white dwarf.

question

what do we mean by a star's life track on a H-R diagram? summarize the stages

answer

EDITThe star life track on an H-R diagram shows how its properties change with time; a red giant should shrink and become less luminous after helium fusion begins in the core

question

explain how the life of a high-mass star differs from that of a low-mass star

answer

Low mass star - Red giant: H fuses He in shell around He core. Double shell fusion: H and He both fuse in shells. Planetary Nebula: leaves white dwarfs. High Mass star - Red supergiant: H fuses to He in shell around He core Multiple shell fusion: many elements fuses in shells Supernova: leaves neutron star behind

question

what event initiates a supernova ; why is a neutron star or black hole left behind? what evidence...

answer

created when the core suddenly collapse, when a degeneracy pressure can no longer resist gravity. The crab nebula is observation evidence and also supernova 1987 which was the first supernova remnants confirm many papers of their models how high mass stars live and die

question

describe the mass, size, ; density of a typical white dwarf

answer

1 solar mass; the radius of the earth; ; the central density is about 1 million times that of water.

question

describe the mass, size, ; density of a typical neutron star

answer

1½ solar masses; a volume approximately 10 km in radius; The density of neutron star material is 10^14 to 10^15 times the density of water

question

how do we know that pulsars are neutron stars? are all neutron stars pulsars?

answer

The first indication was the very short period of some pulsars. Nothing else could rotate that fast without flying apart; not all neutron stars are pulsars. There are some ways by which a neutron star may emit pulses, but the necessary conditions won't exist for all neutron stars; we can detect only those pulsars that emit their energy in our direction.

question

explain how the presence of a neutron star can make a close binary star system appear to us as an x-ray binary

answer

It happens when some neutron stars get enough hydrogen to fuse enough helium to start helium fusion. The helium fusion stops and the hydrogen plies up again, starting the process over.

question

in what sense is a black hole like a hole in the observable universe?

answer

A black hole is like a hole in the observable universe as we can not see inside it

question

why do we think that black holes should sometimes be formed by supernovae? what observational evidence supports the existence of black holes?

answer

A neutron star has a mass limit of about 2 to 3 solar masses. If a supernovae occurs when a star is too massive to become a neutron star, the result is a black hole. Observationally, we can detect black holes through the gravitational influence on other objects and by the way they block out other objects

question

describe & contrast stellar orbits in the disk, halo, & bulge of our galaxy

answer

-Disk stars orbit in circles with the same orientation, except for little up- and- down motion. -Halo Stars travel high above and far below the disk on orbits with random orientations -Bulge Stars also have orbits with random orientations

question

how can we use orbital properties of stars to learn about the mass of the galaxy?

answer

We can use the sun's orbital velocity to determine the mass of our galaxy lying within the suns orbit. We need to consider the difference between the gravitational effects of mass within the suns orbit and those of mass beyond its orbit

question

summarize the stages of the star-gas-star cycle

answer

atomic hydrogen clouds;collapse of molecular clouds;star formation; nuclear fusion in stars;returning gas;hot bubbles;atomic hydrogen clouds

question

O B A F G K M

answer

oh be a fine gay kiss me; temp decreases, uv;uv;violet;blue;yellow;red;infrared

question

visual binary

answer

pair of stars that we can see distinctly

question

spectroscopic binary

answer

seen with observations of Doppler shifts; spectral lines will show alternating blueshifts ; redshifts

question

eclipsing binary

answer

pair of stars that orbit in the plane of our line of sight

question

What kind of gas cloud is most likely to give birth to stars?

answer

a cold, dense gas cloud

question

planetary nebula

answer

Gas ejected from a low-mass star in the final stage of its life

question

nova

answer

an explosion on the surface of a white dwarf in a close binary system

question

neutron star

answer

the remains of a star that died in a massive star supernova (if no black hole was created)

question

pulsar

answer

rapidly rotating neutron stars

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