Astronomy Chapters 17 & 18

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 of the following types of star is the coolest (has the lowest surface temperature)?

M

A star moving toward the Sun will show:

a shift in the spectral lines toward the blue end (as compared to the laboratory positions of these lines)

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)

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

binary stars

Which color star is likely to be the hottest?

blue-violet

At an astronomical conference, an astronomer gives a report on a star that interests astronomers because of hints that it may have a planet around it. In his report the astronomer gives the average speed with which this star is moving away from the Sun. How did the astronomer measure this speed?

by looking at the Doppler shift in the lines of the star's spectrum

A team of astronomers takes spectra of thousands of different stars in different parts of the sky. The spectra show significant differences. The main reason the spectra of the stars do not all look alike is that the stars

have different temperatures

When an astronomer rambles on and on about the luminosity of a star she is studying, she is talking about:

how much energy the star gives off each second

Studies of the spectra of stars have revealed that the element that makes up the majority of the stars (75% by mass) is

hydrogen

If hydrogen is the most common element in the universe, why do we not see the lines of hydrogen in the spectra of the hottest stars?

in the hottest stars, hydrogen atoms are ionized, and so there are no electrons to produce lines in the spectrum

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

its mass

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

more luminous (intrinsically brighter) than the Sun

Two stars have the same luminosity, but star B is three times farther away from us than star A. Compared to star A, star B will look

nine times fainter

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

Two stars have the exact same luminosity, but star Y is four times dimmer looking that star X. This means that

star Y is twice as far away as star X

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

surface temperature

When an astronomer measures a color index for a star, what is she measuring?

the difference between how bright a star looks at two different wavelength regions

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