Astronomy - First Exam

To determine the mass of stars, astronomers study what type of stars?

binary stars

Light acts like?

both a wave and particle

The H-R diagram is uniquely important because it shows what?

Evolution of stars. While the H-R diagram shows the temperatures, colors, and lumiosities of stars, we combine these with the paths that stars take along the diagram to understand how they evolve

Does a star with no carbon absorption lines in its spectrum contain no carbon?

False. A star with no carbon absorption could have no carbon, or the atoms could not be in the right energy state to absorb light.

Star A and star B have the same luminosity, but star A is hotter than star B. What is true of the stars?

Helium is more massive than hydrogen. Helium has four times the mass of hydrogen.

Star A is located at a distance from Earth of 5 parsecs. Star B is located twice as far away, at a distance of 10 parsecs. What star has the larger parallax?

Star A

Consider two stars, A and B, which have the same brightness. If star A is at four times the distance of star B, how do the luminosities of star A and star B compare?

Star A is 16 times more luminous than star B

The Sun has a diameter about 100 times that of Earth. How do the volumes of the Sun and Earth compare?

The Sun has about 100 x 100 x 100 = 1,000,000 times the volume of Earth

Which quantities are plotted on the H-R diagram?

luminosity on the vertical axis; temperature on the vertical axies

Consider a near infrared photon with two times the wavelength of visible red light. This photon of near infrared light has ____ energy of visible red light

one half the

Suppose you have two monochromatic light beams. Beam 1 has half the wavelength of beam 2. How do their frequencies compare?

Beam 1 has 2 times the frequency of beam 2. Frequency and wavelength are inversely related, so if the wavelength is half, the frequency is double

Stars of different spectral classes, O, B, A, F, G, K, and M, show differences in the strengths of absorption lines of various elements. These difference are due mainly to what?

difference in the surface temperature of stars

Knowing the luminosity and brightness of a star allows calculation of what?

distance of the star

Comparing visible light of different wavelengths, a photon of red light ___ a photon of blue light

has a lower energy than

Two stars are of equal luminosity. Star A is 3 times as far from you as star B. Star A appears ___ star B.

1/9 as bright. Star A is father so it must appear fainter. Since brightness scales as 1/d^2 it will appear 3^2=9 times fainter

What is the surface temperature of a star that has a peak wavelength of 290nm?

10,000 K. Using Wein's Law, T = (2.9 x 10^6)/λ

Assume that two stars can be considered as ideal blackbodies. A red star which has a surface temperature of approximately 3,000 K would have maximum emission at a wavelength of 1,000nm. A blue star with a surface temperature of about 30,000 K would have maximum emission at a wavelength of what?

100 nm

Suppose an atom has three energy levels, specified in arbitrary units as 10, 7, and 5. In these units, which of the following energies might an emitted photon have?

3, 2, 5 since we have 10-7, 10-5, and 7-5

Light from the Sun reaches the Earth about ___ after it leaves the Sun?

8 minutes

Star A is twice as bright as star B, but also twice as far away. Star A is ___ as luminous as star B

8 times. Brightness b changes as L/d^2, so the fact that star A appears twice as bright but is twice as far away means that 2 x 2^2= 8

What spectral type of stars has the most pronounced hydrogen Balmer absorption lines (in the visible)?

A

Why is an iron atom a different element from a sodium atom?

An iron atom has more protons in its nucleus than a sodium atom has. A given element is defined by its number of protons.

Antares is a red star of spectral class M, Spica is a blue star of spectral class B. What is true?

Antares is cooler than Spica.

The temperature of an object has a very specific meaning as it relates to the object's atoms. A high temperature means what?

Atoms are moving very fast. Temperature is a measure of the energy is an object, and since the object is made of atoms, it is equivalently a measure of the speed of the atoms.

Can an atom emit or absorb a photon of any wavelength?

False. An atom can only emit energies corresponding to the quantized energy levels of its electrons

Are brighter stars always more luminous than fainter stars?

False. Brightness depends on distance as well as luminosity.

Do cooler objects radiate more of their total light at shorter wavelengths than do hotter objects?

False. Cooler objects radiate redder light.

Is the emission spectrum of a helium atom identical to that of a carbon atom?

False. Every atom has its own energy levels, depending on the size and charge of the nucleus and the electron structure

Are hotter stars always redder than cooler stars?

False. as blackbodies, hotter stars are bluer.

How many times larger in diameter is the "huge" planet of Jupiter than the Earth?

Jupiter is ten times the diameter of Earth

The fifty nearest starts to Earth are in what spectral type?

M

What spectral type of star shows many absorption lines of molecules and neutral "metals?"

M

As a blackbody becomes hotter, it also becomes ___ and ___.

More luminous and bluer

In spectral type of stars would absorption lines from highly ionized atoms (such as He II, Si IV) be strongest?

O

Star A and Star B are two stars exactly the same color. Star A's calcium absorption lines are deeper than star B's. What is true of the stars?

Star A has more calcium than Star B. For two identical stars, the depth of the absorption line indicates the amount of the element present.

Star A and star B are a binary system. The doppler shift of star A's absorption lines is 3 times the Doppler shift of star B's absorption lines. What is true of the stars?

Star A is 1/3 as massive as star B. Star A is moving three times faster than star B; therefore, it must be less massive.

Star A and star B are two nearby stars. Star A has a parallactic angle 4 times as large as star B's. What is true of the stars?

Star A is 1/4 as far away as star B. More distant stars have smaller parallax angles.

Star A and star B appear equally bright in the sky. Star A is twice as far away from Earth as star B. How do the luminosities compare?

Star A is 4 times as luminous as star B. Brightness sacles as L/d^2 so if star A is twice as far away, it must have 2^2=4 times more luminosity to appear as bright as star B.

Star A and star B are two blue stars at nearly the same distance from Earth. Star A is many times brighter than star B. What is true of the stars?

Star A is a blue giant, and star B is a white dwarf. If stars are at the same distance, then brightness indicates luminosity. Since Star A is brighter than B but the same color, then it must be large. We can rule out either star being red giant because of the blue color.

Star A and star B are two red stars at nearly the same distance from Earth. Star A is many times brighter than star B. What is true of the stars?

Star A is a red giant, and star B is a main-sequence star. If stars are at the same distance, then brightness indicates luminosity. Since star A is brighter than B but at the same temperature, it must be larger; that is, A is a giant, and B is a dwarf or main-sequence star.

Star A and star B are two nearby stars. Star A is blue, and star B is red. What is true of the stars?

Star A is hotter than star B. Since a star acts like a blackbody, we know that a bluer intrinsic color means the star's surface is hotter.

Capella is the sixth-brightest star in the sky. When viewed with a high-power telescope, it is clear that Capella is actually two pairs of binary stars: the first pair are G-type giants; the second pair are M-type main-sequence stars. What color does Capella appear to be?

Star A is smaller than star B. L ∞ R2 T2, so if one star is hotter, it must be smaller to have the same luminosity as the cooler one.

Star A and star B are two stars nearly the same distance from Earth. Star A is blue, and star B is red, but they have equal brightness. What is true of the stars?

Star A is smaller than star B. Since the stars are at the same distance and appear the same brightness, they must have the same luminosity. The fact that one is red means it is cooler; therefore, it must be larger to have the same luminosity as the blue star.

Star A is one quarter times the radius of star B. Star A has twice the temperature of star B. Which statement is true about the relative luminosities of these two stars?

Star A is the same luminosity as star B

Star A and Star B are two stars at nearly the same distance from Earth. Star A is half as bright as star B. What is true of the stars?

Star B is twice as luminous as star A. Since the two stars are the same distance, the only reason one would appear brighter is if it is more luminous

How does the speed of light in a medium compare to the speed of the vacuum?

The speed in the medium is always slower than the speed in the vacuum. In any medium, light slows down.

Does blue light have more energy than red light?

True. Blue light has more energy than red light.

In a binary system, do more massive stars move more slowly than a less massive star?

True. Conservation of momentum, dictates that the more massive star moves more slowly.

Is the frequency of a photon related to the energy of a photon?

True. E=hf

Is the mass of a star the primary indicator of its observable properties?

True. Once one knows the mass of a star, then its size, temperature, and luminosity are known, but provided one also knows its evolutionary state.

When an electron in an atom falls from a higher energy level to a lower energy level, what happens?

a photon is emitted by an atom

When an electron moves from a higher energy level in an atom to a lower energy level, a photon does what?

a photon is emitted. A downward transition gives off energy, meaning a photon is emitted.

Star A is more massive than star B. Both are main sequence stars. Therefore, star A is ____ than star B.

brighter, hotter, larger. Since both stars are main-sequences, more massive implies hotter, larger, and more luminous.

Choose the two qualities that describe a star located in the lower right of the H-R diagram.

cold and faint. The lower right of the H-R diagram is low temperature with low luminosity.

Suppose we observe a cool, tenuous gas with a hotter blackbody behind it. The combined spectrum will be ___

continuous radiation with absorption lines superimposed

Stars of spectral type L and T have what characteristics?

cool (surface temp about 1500 - 2500 K), small objects, appearing brightest in the infrared

The reason most stars are main-sequence stars is that the main sequence phase is what?

longest part of a star's lifetime. Most stars are main-sequence stars; since the stage accounts for about 90 percent of any star's lifetime, we see most stars during their longest-lived phases.

The property of a star which determines its luminosity when on the Main Sequence is its what?

mass

Momentum is the product of what?

mass and energy. This is the classical definition

Why are they hydrogen Balmer absorption lines weak in cool stars (such as spectral type M)?

most of the hydrogen is in the ground level (n=1)

The Doppler shift of absorption or emission lines in a star's spectrum is used to find the star's what?

radial velocity?

Which is the largest measurement of an angle?

radian. A radian is about 57.3 degrees while an arcmin and arcsec are fractions of a degree.

Rank the following in order of decreasing wavelength? gamma rays, visible light, infrared light, ultraviolet light, radio waves

radio waves, infrared, visible light, ultraviolet light, gamma rays

O stars have relatively featureless visible spectra because O stars are what?

so hot that most atoms are ionized. The high temperatures of O stars men that most atoms are either ionized or the electrons are in such high-energy states that they will not absorb many photons to produce absorption lines.

The property of a star which determines its spectral type is its what?

surface temperature

When less energy is radiated from a terrestrial planet, its ___ increased until new ___

temperature; equilibrium. If less energy is radiated away, the energy is trapped, making the temperature increase to a new equilibrium level

When a boat moves through the water, the waves in front of the boat bunch up, while the waves behind the boat spread out. What is this an example of?

the Doppler effect. The Doppler effect explains why waves are compressed in the direction of motion and stretched out in the opposite direction

If planet is in thermal equilibrium, what is energy doing?

the amount of energy leaving equals the amount of energy arrive. Stuff in equals stuff out.

A telescope on Mars would be able to measure the distances to more stars than can be measured from Earth. Why?

the baseline would be longer. Since parallax depends on the distance of the planet from the Sun, a large orbital distance would make the pc longer and would allows us to see parallax motion of more distance stars.

Comparing the twenty five brightest stars in the sky with the fifty nearest stars in the sky, what is true?

the brightest stars are generally larger (radius) than the nearest stars

A certain spectral line is observed in the laboratory to occur at wavelength of 500nm. In the spectrum of a star, the line blueshifted, being observed at a wavelength of 499nm. The star is moving how fast?

the star is approaching 1/500 times the speed of light

Most stars, including the Sun, have dark lines in their spectra. We say that the stars have absorption line spectra. What does this fact imply about the physical conditions in the stars

the stars are made up of a hot opaque gas, surrounded by a transparent gas of a lower temperature

List the follow electromagnetic waves in increasing order of wavelength: radio waves, infrared, visible light, ultraviolet, x-ray

x-ray, ultraviolet, visible light, infrared, radio waves