Chapter 18 Astro

What was the first evidence that gravity outside our solar system worked the same way as it does inside?

Herschel measured the two stars that make up the Castor system moved around each other

Who was the astronomer who is the "H" in H-R diagram?

Hertzsprung

Which law do astronomers use to determine the masses of the stars in a spectroscopic binary system?

Kepler's Third Law

Which of the following has the smallest mass?

a planet

A star that is quite hot and has a very small radius compared to most stars is called

a white dwarf

In an H-R diagram, where can you see the spectral type of a star (whether it is an O type star or a G type star, for example)?

along the bottom (the horizontal axis)

One of your good friends who is on a diet asks you to point out the stars with the smallest mass on an H-R diagram that you are studying. Where are you sure to find the stars with the lowest mass on any H-R diagram?

among the stars at the bottom right of the main sequence

Which of the following statements about spectroscopic binary stars is FALSE?

an analysis of the ways the lines in the spectrum change allows us to calculate the star's distance directly

Some "superstars" give off more than 50,000 times the energy of the Sun. Why are there no such stars among the stars that are close to the Sun?

because such very luminous stars are extremely rare, and thus any small neighborhood in the Galaxy is unlikely to contain one of them

Two stars that are physically associated (move together through space) are called

binary stars

Stars that do not have what it takes to succeed as a star (i.e. do not have enough mass to fuse hydrogen into helium at their centers) are called:

brown dwarfs

For what type of star can astronomers measure the diameter with relative ease?

eclipsing binary stars

Astronomers identify the main sequence on the H-R diagram with what activity in the course of a star's life?

fusing hydrogen into helium in their cores

Imagine that powerful telescopes in the future give us a truly representative sampling of all the stars in the Sun's cosmic neighborhood. Where on the H-R diagram would most of the stars in our immediate vicinity lie?

in the lower right, among the least luminous main sequence stars

Measurements show a certain star has a very high luminosity (100,000 x the Sun's) while its temperature is quite cool (3500o K). How can this be?

it must be quite large in size

Which of the following characteristics of a single star (one that moves through space alone) is it difficult to measure directly?

its mass

The most common kinds of stars in the Galaxy have

low luminosity compared to the Sun

Stars on the main sequence obey a mass-luminosity relation. According to this relation,

luminosity is proportional to mass to the fourth power (luminosity increases strongly with mass)

Stars that lie in different places on the main sequence of the H-R diagram differ from each other mainly by having different:

masses

Most of the stars we can see with the unaided eye from Earth are

more luminous (intrinsically brighter) than the Sun

Which of the following is a method for measuring the diameter of a star?

more than one of the above

A team of astronomers discovers one of the most massive stars ever found. If this star is just settling down in that stage of its life where it will be peacefully converting hydrogen to helium in its core, where will we find it on the H-R diagram?

near the very top of the main sequence, in the upper left

Where on the H-R Diagram would we find stars that look red when seen through a telescope?

only on the right side of the diagram and never on the left

A white dwarf, compared to a main sequence star with the same mass, would always be:

smaller in diameter

Why can astronomers not measure the diameters of stars directly?

stars are so far away, we cannot resolve (distinguish) their diameters

An H-R Diagram plots the luminosity of stars against their:

surface temperature

I am measuring the spectrum of the stars in a spectroscopic binary system. When one of the stars is moving toward the Earth in its orbit, we observe

that the lines in its spectrum show a blue-shift

Ninety percent of all stars (if plotted on an H-R diagram) would fall into a region astronomers call:

the main sequence

Most of the really bright stars in our sky are NOT among the stars that are very close to us. Why then do they look so bright to us?

these stars are intrinsically so luminous, that they can easily be seen even across great distances