Astronomy 2012

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University of Windsor Midterm

Which of these is not a form of electromagnetic radiation?

DC current from your car battery

The speed of light in a vacuum is

300,000 km/sec

If a wave's frequency doubles, its wavelength

is halved

What is the name of the temperature scale that places zero at the point where all atomic and molecular motion ceases

Kelvin

The sums observed psectrum is

a continuum with absorption lines

In Bohr's model of the atom, electrons

only make transitions between orbitals of specific energies

The total energy radiated by a blackbody depends on

the fourth power of its temperature

A jar filled with gas is placed directly in front of a second jar filled with gas. Using a spectroscope to look at one jar through the other you observe dark spectral lines. The jar closes to you contains

the cooler gas

In general, the spectral lines of molecules are

more complex than those of atoms

The two forms of EM radiation that experience the least atmospheric opacity are

light and radio waves

the observes spectral lines of a star are all shifted towards the red end of the spectrum. Which statement is true?

this is an example of the Doppler effect

Which of these is the same for all forms of EM radiation in a vacuum?

Velocity

Medium A blocks more of a certain wavelength of radiation that medium B. Medium A has a higher

Opacity

The primary purpose of a telescope is to

collect a large amount of light and bring it into focus

The angular resolution of an 8 inch diameter telescope is ____ greater than that of a 2 inch diameter telescope

4x

the amount of diffraction and thus the resolution of the scope depends on

the brightness of the object

what is the resolution of a telescope?

its ability to distinguish two adjacent objects close together in the sky

compared to a 5 inch prime focus reflector, a 5 inch Newtonian reflector will

have the same light gathering power

What is the light gathering power of an 8 inch telescope compared to a 4 inch?

4x better

Green light has a shorter WL than orange light. In a 5 inch telescope, green light will

provide better angular resolution than orange light

What problem does adaptive optics correct

Turbulence on the earths atmosphere that creates twinkling

Most radio telescopes are laid out which optical telescope design?

Prime focus reflector

in astronomy, interferometry can be used to

improve the angular resolution of the radio telescopes

The temperature of the photosphere is about

5,800K

What is the meaning of the solar constant?

the amount of energy the Earth receives per unit area and unit time

What two energy transport mechanisms, in order from outside the core to the surface, are found in
the Sun?

radiation, convection

The outward pressure of hot gas in the Sun

is balanced by the inward gravitational pressure.

The solar winds blow outward from

coronal holes

From inside out, which is in the correct order for the structure of the Sun?

radiative zone, convective zone, chromosphere

How long does the sunspot cycle last, on average?

about 11 years

Visible sunspots lie in the

granualtion in the photosphere

As the Sun rotates, an individual sunspot can be tracked across its face. From eastern to western
limb, this takes about

two weeks

The most striking example of solar variability was the

Maunder Minimum from 1645-1715

Sunspots

come in pairs representing the north and south magnetic fields

During a period of high solar activity, the corona

is more irregular

Sunspots are dark splotches on the Sun. Which statement is true?

they are extremely hot, but cooler than the surrounding areas of the sun

While observing the Sun, you note a large number of sunspots. What can you conclude?

There are likely to be an above average number of flares and prominences.

The critical temperature to initiate the proton-proton cycle in the cores of stars is

10 million K.

In the proton-proton cycle, the helium atom and neutrino have less mass than the original
hydrogen. What happens to the "lost" mass?

It is converted to energy.

The primary source of the Sun's energy is

the strong force fusing hydrogen into helium.

In the proton-proton cycle, the positron is

an anti-electron.

Which is the net result of the proton-proton chain?

4 protons = 1 helium 4 + 2 neutrinos + gamma rays

Hydrogen "burning" by fusion reactions occurs only in the deep interior of the Sun (and
other stars), because
this is the only place in the Sun where

the requisite conditions of high temperature and high density occur

What happens to the positrons produced by the nuclear reactions in the core of the Sun?

they collide with electrons, producing energy

Which of these are not associated with the active Sun?

granulation

Which statement about stellar motion is incorrect?

proper motion is measured in intervals of 6 months

A star has a parallax of 0.01 arc seconds. Its distance is

100 parsecs

If Vega is apparent magnitude zero, and Deneb first magnitude, then

vega must be 2.5x more luminous than deneb

A star's absolute magnitude is its apparent brightness as seen from

10 parsecs distance

Two stars both have parallaxes of 0.023", but star A has apparent magnitude +2.3, while star B is
magnitude +7.3. Which statement is true?

star A is both 100x brighter and more luminous than star B

What physical property of a star does the spectral type measure?

temperature

Which of these stars would be the hottest?

B0
(B0, M10, k9,g2,a0)

What can be said with certainty about a red star and a blue star?

the blue star is hotter than the red star

Compared to a type A0 star, a type A9 star is

cooler

the star's color index is a quick way of determining its

temperature

The H-R diagram can plot

temperature vs. luminosity

In the H-R diagram, what are the two most important types of data plotted?

spectral classes and absolute magnitudes

On the H-R diagram, the Sun lies

about the middle of the main sequence

On the H-R diagram, white dwarfs Sirius B and Procyon B lie

at the top left

On the H-R diagram, red supergiants like Betelgeuse lie

at the top right

A star near the lower right of the H-R diagram is likely to be

red, with low illuminosity

The Doppler shift is used to find

spectroscopic boundaries

Which type of binary do we get information about by looking at the intensity of light?

eclipsing

Binary stars separated enough to be resolved in a telescope are called

visual binaries

apparent angular movement of a nearby star against the background stars as a consequence of
its motion in space is known as

proper motion

The speed of a star, measured in a direction perpendicular to the line of sight from the Earth to the
star, is known as

transverse velocity

Suppose that two identical stars (having the same total light output or luminosity) are located such
that star A is at a distance of 5 pc and star B is at a distance of 25 pc. How will star B appear,

1/25 as bright

Light, leaving a point source, spreads out so that the apparent brightness, I , of light per unit area
varies with distance d according to which law (μ means "proportional to")?

A) I µ 1/d 2

Interstellar gas is composed mainly of

90% hydrogen, 9% helium by weight.

What happens to light passing through even thin clouds of dust?

It dims and reddens the light of all more distant stars.

Which statement about dark dust clouds is true?

They can be penetrated only with longer wavelengths such as radio and infrared.

Some regions along the plane of the Milky Way appear dark because

stars in that region are hidden by dark dust particles.

Emission nebulae like M42 occur only near stars that emit large amounts of

UV radiation

what is the primary visible color of an emission nebula?

red due to ionized hydrogen atoms

Due to absorption of shorter wavelengths by interstellar dust clouds, distant stars appear

larger

The spectra of interstellar gas clouds show that they have the same basic composition as

stars

Which statement is true about the interstellar medium?

We know more about the gas than the dust.

The density of interstellar dust is very low, yet it still blocks starlight because

the dust particles are about the same size as the light waves they absorb.

What two things are needed to create an emission nebulae?

hot stars and interstellar gas, particularly hydrogen

A large gas cloud in the interstellar medium that contains several type O and B stars would appear
to us as

an emission nebulae

Neutral hydrogen atoms are best studied from their energy given off as

21-cm waves in the radio region.

Complex molecules in the interstellar medium are found

primarily in the dense dust clouds

Why are dark dust clouds largely misnamed?

the contain much more gas than dust

The average temperature of the typical dark regions in space are

100K

Interstellar dust clouds are best observed at what wavelength?

radio

Which of these is not a consequence of dust in the interstellar medium?

red light from the emission nebulae

It is important to study interstellar dust because

A) there is almost as much mass between the stars as therre is in them.
B) this is where stars are formed.
C) old stars expel their matter here when they die.
D) all of the above.

Reflection nebula have their blue colour because

the interstellar dust deflects the blue light.

What is true of emission nebula?

A) they are often part of much larger interstellar clouds.
B) their temperature can exceed that of our sun.
C) they are bigger than earth.
D) they produce an emission spectrum.
E) All of the above.

When an electron in hydrogen changes its spin from the same to the opposite direction as the
proton, it

emits radio wave photon

During the T-Tauri phase of a protostar, it

may develop very strong winds.

What is the critical core temperature required for fusion?

10 million K

Which statement about the stages of starbirth is false?

*A) nuclear reactions begin in the core by stage 4.*
B) The T-Tauri wind is prevalent in stage 5.
C) By stage 3, the star has formed a photosphere.
D) At stage 1, only the cloud exists.
E) By stage 7, the star has reached the main sequence.

On an H-R diagram, a protostar would be

above and to the right of the main sequence.

The single most important determinant of the temperature, density, radius, luminosity,
and pace of evolution of a protostar is its

mass

A cloud fragment too small to collapse into a main sequence star becomes a

brown dwarf

All globular clusters in our Milky Way are about how old?

around 10 billion years old

Why are star clusters ideal "laboratories" for stellar evolution?

Their stars are all about the same age, composition, and distance from us.

Which of these would typically be the brightest star in a young open cluster?

B1V

What are the characteristics of an open cluster of stars?

a few hundred, mostly main-sequence stars

Which of these would be the brightest star in an ancient globular cluster?

K3

Which is characteristic of globular star clusters?

old age and hundreds of thousands of stars, only about 50 pc wide

How long does it take an M-type star to reach the main sequence, compared to a
solar-type star?

about twenty times longer

A fragment of a collapsing gas cloud that comes to equilibrium with a central
temperature of 4 million K will become a

brown dwarf

Why are the majority of stars in the sky in the main sequence phase of their lives?

This is the longest-lasting phase in each star's life.

Which of the following statements about the rate of stellar evolution is true?

The more massive the original star, the faster the evolution.

Which of the following are NOT very young stars or prestellar objects?

red giants

Within a globular cluster, what would you expect to find in the population of stars?

many red giants, white dwarfs, and dim red stars but no bright blue stars or dust
and gas

ZAMS stands for:

zero age main sequence

In what stage of evolution is a star formed?

stage 6

In what stage of evolution is the forming star the brightest?

stage 4

What is the importance of nebular clouds that surround newly forming stars?

They add mass to the star during formation.

What is NOT true of successful star formation?

Planets are formed out of the nebular cloud.

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