chapter 2

Question 1

What is a dwarf star?

Answer 1

main-sequence star

Question 2

What is a white dwarf star?

Answer 2

star of about the same size (diameter) as Earth

Question 3

compositions of white dwarfs

Answer 3

carbon and oxigen

Question 4

nova

Answer 4

binary star

Question 5

binary stars are made of

Answer 5

white dwarf and another dead star

Question 6

How far away is the nearest star beyond the Sun?

Answer 6

about 4 ly away

Question 7

What is parallax?

Answer 7

apparent shift in position of an object as the observer moves

Question 8

The motion that is used to change the position of the observer in the most common parallax measurements of distances to relatively nearby stars is the

Answer 8

motion of Earth in its orbit around the Sun.

Question 9

Stellar parallax appears because

Answer 9

Earth moves in space.

Question 10

Apparent magnitude is a measure of a star’s

Answer 10

brightness, as seen from Earth.

Question 11

A star of apparent magnitude +1 appears _____ than a star of apparent magnitude +2.

Answer 11

brighter

Question 12

The statement that the apparent magnitude of a variable star has increased indicates that its

Answer 12

brightness has decreased

Question 13

Luminosity is measured in

Answer 13

watts

Question 14

The luminosity of a star is

Answer 14

its total energy output into all space

Question 15

An astronomer is measuring the brightness of a particular star through a telescope, using different filters in the visual (yellow-green), violet, and ultraviolet regions. What is the name of the technique being used by this astronomer?

Answer 15

photometry

Question 16

For Balmer series lines to show up strongly in absorption in stellar spectra, significant numbers of hydrogen atoms have to have electrons in the n = 2 energy level. What then does the appearance of these lines in a stellar spectrum tell us about the temperature of the star’s surface?

Answer 16

The temperature must be reasonably high to excite the electrons to this level by collisions but not high enough to ionize the atoms.

Question 17

Why is there a limited range of stellar surface temperatures around 10,000 K at which neutral hydrogen gas absorbs visible light in the Balmer series?

Answer 17

Electrons in hydrogen have to be at the n = 2 energy level to produce absorption in this series. If the gas is too cold, most atoms are in the n = 1 state; if it is too hot, most atoms are ionized

Question 18

The chemical makeup of the Sun’s surface can be determined by

Answer 18

solar spectroscopy.

Question 19

Which of the following spectral classification letters signifies the hottest stellar surface temperature?

Answer 19

B

Question 20

Which of the following four spectral classifications signifies the coolest stellar surface temperature?

Answer 20

K

Question 21

The Hertzsprung-Russell diagram is a plot of

Answer 21

absolute magnitude (or intrinsic brightness) against temperature of a group of stars

Question 22

If you compare two stars, the one with the _____ must have the greater luminosity.

Answer 22

smaller absolute magnitude

Question 23

What are the two physical parameters of stars that are plotted in the Hertzsprung-Russell diagram?

Answer 23

luminosity and surface temperature

Question 24

Compared with a star in the middle of the Hertzsprung-Russell diagram, a star in the lower left of the diagram is

Answer 24

smaller

Question 25

Compared with a star in the middle of the Hertzsprung-Russell diagram, a star in the upper right of the diagram is

Answer 25

larger.