Chapter 11: Surveying The Stars

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surveying the stars

What is the approximate chemical composition (by mass) with which all stars are born?

three quarters hydrogen, one quarter helium, no more than 2% heavier elements

The total amount of power (in watts, for example) that a star radiates into space is called its _________.

luminosity

According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples?

Its apparent brightness will decrease by a factor of 9.

Assuming that we can measure the apparent brightness of a star, what does the inverse square law for light allow us to do?

Calculate the star's luminosity if we know its distance, or calculate its distance if we know its luminosity.

If star A is closer to us than star B, then Star A's parallax angle is _________.

larger than that of Star B

Ten parsecs is about _________.

32.6 light-years.
(1 parsec=3.26 ly)

Star A has an apparent magnitude of 3 and star B has an apparent magnitude of 5. Which star is brighter in our sky?

Star A

From hottest to coolest, the order of the spectral types of stars is _________.

OBAFGKM

Our Sun is a star of spectral type _________.

G (2)

Astronomers can measure a star's mass in only certain cases. Which one of the following cases might allow astronomers to measure a star's mass?

The star is a member of a binary star system

Which of the following terms is given to a pair of stars that we can determine are orbiting each other only by measuring their periodic Doppler shifts?

spectroscopic binary

The axes on a Hertzsprung-Russell (H-R) diagram represent _________.

luminosity and surface temperature

What can we infer, at least roughly, from a star's luminosity class?

its size

On an H-R diagram, stellar radii _________.

increase diagonally from the lower left to the upper right

On an H-R diagram, stellar masses _________.

can be determined for main sequence stars but not for other types of stars

How is the lifetime of a star related to its mass?

More massive stars live much shorter lives than less massive stars. (Small stars are fuel-efficient like a Prius)

What is the common trait of all main sequence stars?

They generate energy through hydrogen fusion in their core.

Suppose our Sun were suddenly replaced by a supergiant star. Which of the following would be true?

Earth would be inside the supergiant.

What is a white dwarf?

the remains of a star that ran out of fuel for nuclear fusion.

What do we mean by the main-sequence turnoff point of a star cluster, and what does it tell us?

It is the spectral type of the hottest main sequence star in a star cluster, and it tells us the cluster's age.

Things we can observe directly:

spectral type, color apparent brightness, parallax angle.

Things we have to infer indirectly:

mass, radius, luminosity, surface temperature.

What must we measure directly so that we can infer a star's surface temperature?

Spectral type

Which of the following must be true if we are to infer (calculate) a star's luminosity directly from the inverse square law for light?

-No interstellar gas or dust absorbs or scatters light between us and the star.

-We have measured the star's apparent brightness.

-We have measured the star's distance

We can measure a star's mass directly if __________.

it is a member of an eclipsing binary system.

Which of the following must be true if the star's inferred mass is to be accurate?

-We have determined that the star is a main-sequence star.

-We have measured the star's spectral type.

Supergiants

the very largest and brightest of all stars

Stars are classified on the basis of their-

spectral type and luminosity class

Cepheids are examples of ________.

pulsating variable stars.

Stars that are cooler than the SUn yet 100 to 1,000 times as luminous as the Sun are ______.

GIANTS

Red giant or supergiant stars:

-very cool but very luminous

-found in the upper right of the H-R diagram

Main-sequence stars:

-the majority of stars in our galaxy

-The Sun

-very hot and very luminous star

White Dwarfs:

-not much larger in radius than Earth

-very hot but very dim

Main-sequence stars during their formation process:

Take longer time forming if lower mass (M)

Take shorter time forming if higher mass (O)

Which of the following stars has a spectrum that peaks at the highest frequency?

blue star

The age of stars in a cluster can be determined by

determining the main sequence turnoff point

What correctly states the relationship between the apparent brightness, luminosity, and distance of a star?

apparent brightness= luminosity/4(3.14159) X (distance)^2

If the distance between us and a star is doubled, with everything else remaining the same, its luminosity

remains the same, but its apparent brightness is decreased by a factor of four.

Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ?

mass they are formed with

The total amount of power (in watts, for example) that a star radiates into space is called its ________.

luminosity

Parallax angle

The angle subtended by a star to the line between the Sun and the Earth
(the Earth-star-Sun angle)

Apparent Magnitude

The brightness a star appears to be from the Earth. The brightest star has a magnitude of 1 and a star 100 times dimmer a magnitude of 6

Absolute Magnitude (Luminosity)

A star's apparent magnitude if it were placed 10 parsecs from the Earth

Stefan's Law

The total energy per second emitted by a black body is proportional to its surface area and to absolute temperature to the fourth power

Parallax: d=

1/p

Inverse-square law: equation?

apparent brightness= (absolute brightness)/d^2

Binary Stars: three types of binary stars?

Visual
Spectroscopic
Eclipsing

Binary Stars: which deals with orbits?

Visual

Binary Stars: which deals with a review of doppler effect, spectral lines, double, and single lines?

Spectroscopic

Binary Stars: which type deals with the mass and radii of stars?

Eclipsing

Doppler Effect: deals with _____ velocity

radial

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