Astronomy Exam 3

What astronomers refer to as a "standard candle" is defined as a light source whose

absolute magnitude is known.

In a particular binary star system, we are able to determine the masses and diameters of both stars This system is most likely

an eclipsing spectroscopic binary system.

A star with an apparent magnitude of 5.7 and an absolute magnitude of -1.2 would appear in our sky as a star

barely visible to the naked eye.

A spectrum that is shifted to shorter wavelengths is said to show a _______ shift and indicates an _______ source.

blue, approaching

A star with an absolute magnitude of 5.7 and an apparent magnitude of -1.2 would appear in our sky as a star

of dazzling brightness.

For a visual binary star system, we can determine

the masses of both stars in the system.

A star at a distance of 1000pc should have an apparent brightness equal to its absolute brightness multiplied by

10^-4

The apparent brightness of our Sun is roughly 1000 watts per square meter. At a distance of 30 times the Earth-Sun distance, the apparent brightness of our Sun would be

1.1 watts per square meter.

How many parsecs would a star with a distance modulus of zero would have to be from us?

10 parsecs

A star is found to have absolute magnitude 4 and apparent magnitude 19. How far away is it?

10,000 parsecs

A star is observed to have an apparent brightness which is 10-6 times its absolute brightness. How far away is it?

10,000 parsecs.

Suppose that the color and behavior of a star identify it as a type that we know has absolute magnitude -3. If the star's apparent magnitude is found to be 2, how far away is it?

100 parsecs

Suppose that the color and behavior of a star identify it as a type that we know has absolute magnitude 4.8. If the star's apparent magnitude is found to be 9.8, how far away is it?

100 parsecs

A star is found to have absolute magnitude 4 and apparent magnitude 24. How far away is it?

100,000 parsecs. (d = 10^20/5 × 10pc = 10^4×10pc.)

Cruising far from the Sun, we notice that the Sun's apparent brightness has dimmed to 0.1 watts per square meter. We know that the apparent brightness at a distance of 1au is 1000 watts per square meter. How far from the Sun are we?

100au

Suppose that a sound wave has a wavelength of 12 meters and a frequency of 100Hz. What is the speed of sound?

1200 m/s

Suppose that a flash of lightning from a cloud 2500 meters away is followed by a clap of thunder two seconds later. Assume that the light arrived in a negligible time and calculate the speed of the sound waves.

1250m/s

Suppose that a sound wave has a wavelength of 2 meters and a frequency of 1000Hz. What is the speed of sound?

2000 m/s

Suppose that a flash of lightning from a cloud 5000 meters away is followed by a clap of thunder two seconds later. Assume that the light arrived in a negligible time and calculate the speed of the sound waves.

2500m/s

The velocity of sound waves is roughly the same for all wavelengths. Suppose that a sound wave has a wavelength of one meter and a frequency of 1000Hz. The wavelength of a 500Hz sound wave would then be

2m

Under city lights, magnitudes above _____ cannot normally be seen with the naked eye.

4

The velocity of sound waves is roughly the same for all wavelengths. Suppose that a sound wave has a wavelength of one meter and a frequency of 1000Hz. The wavelength of a 250Hz sound wave would then be

4m

You hear a 1000Hz tone from a radio that is 10 feet away from you and listen for 5 seconds. How many pressure maxima pass by your ear?

5000

Under magnitudes as high as ___ can be seen with a dark-adapted naked eye with perfect sight

6

The red line of a spectrum is normally at a wavelength of 656 nm. In the light of a star that is moving away from us, we might expect to see that red line at a wavelength of

660nm

What is the energy per unit time per unit area that enters our telescope.

Apparent brightness

Of all the things that might go wrong with distances found by using the method that astronomers refer to as the "distance ladder," which of these is the one that an astronomer would say is most likely?

Distant objects are not behaving the same as nearby objects.

Which of these answers describes the fundamental assumption that is behind all of the methods that astronomers refer to as the "distance ladder?"

Distant objects are similar to nearby objects.

What does the inverse law say?

If you multiply the distance by some number, you divide the apparent brightness by the square of that number.

What is the total light output of the star (the energy emitted per unit time) called?

Luminosity

What is distance modulus?

The difference between apparent magnitude and absolute magnitude (apparent - absolute)

The frequency of a wave is defined to be

The number of crests that pass in one second.

We see what appears to be a single star. However, when the light from the star is put through a spectrometer, we see two distinct spectra, shifting back and forth. The star is actually

a double-line spectroscopic binary system.

We see what appears to be a single star. However, when the light from the star is put through a spectrometer, we see that its spectrum is shifting back and forth. The star is most likely

a single-line spectroscopic binary system.

In a particular binary star system, we are able to determine the masses of both stars in the system as well as the angle between our line of sight and the plane of the stars' orbits but cannot determine the diameters or atmospheric compositions of the two stars. This system is most likely

a visual binary system.

In a particular binary star system, we are only able to determine a minimum mass for each star and cannot determine the angle between our line of sight and the plane of the stars' orbits. This system is most likely

a visual binary system.

What does apparent magnitude describe?

how bright the star looks to us.

What does absolute magnitude describe?

how bright the star really is.

If a star is dim is its magnitude a larger or smaller number?

larger

Suppose that a star has a spectrum that includes red, blue, and violet lines spaced in the pattern of the lines from hydrogen but the violet lines are at 444nm and 420nm instead of the usual 434nm and 410nm. From this evidence, you can conclude that the star is

moving away from us.

Suppose that a star has a spectrum that includes red, blue, and violet lines spaced in the pattern of the lines from hydrogen but the violet lines are at 424nm and 400nm instead of the usual 434nm and 410nm. From this evidence, you can conclude that the star is

moving toward us.

For a spectroscopic binary star system, we can determine

only a minimum mass for each star.

A spectrum that is shifted to longer wavelengths is said to show a __________ shift and indicates a ________ source.

red, receding

If a star is bright is its magnitude a larger or smaller number?

smaller

Consider a light source whose absolute magnitude can be deduced from the properties of the light that reaches us from that source. Astronomers often refer to this sort of object as a

standard candle

The wavelength of a wave is defined to be

the distance from one crest to the next.

The velocity of a wave is defined to be

the distance traveled by a crest divided by the time taken.

For an eclipsing spectroscopic binary star system, we can determine

the masses and diameters of both stars in the system.

The wavelength of the sound waves that correspond to middle-C is about 4 feet. If you are standing 8 feet away from a piano that is playing that note, then between you and the piano there will usually be

two regions of maximum pressure.