Astronomy #2 – Flashcards

Flashcard maker : Kaitlynn Baldwin
The “dust” component of the interstellar medium is mostly particles of about what size?
smoke particles

The red/pink color associated with star-forming regions is due to what kind of process?
emission

What kind of light would be the best to use to look inside a cold dark cloud and see the warm stars forming inside?
infrared

Why does dust redden starlight?
It scatters optical and shorter-wavelength light.

Interstellar gas is composed mainly of
90% hydrogen, 9% helium by weight.

Some regions along the plane of the Milky Way appear dark because
stars in that region are hidden by dark dust particles.

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.

Of all forms of electromagnetic energy, _____ radiation gives us the least access to our entire Milky Way Galaxy.
visible light

What type of nebula contains stars of spectral types O and B?
an emission nebula

What causes the striking red color associated with some parts of many emission nebulae?
electrons in hydrogen atoms making transitions from their n = 3 to n = 2 atomic states

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

Emission nebulae occur only near stars that emit large amounts of _____ electromagnetic radiation.
ultraviolet

The most common molecule in a molecular cloud is
molecular hydrogen, H2.

What information does 21-cm radiation provide about the gas clouds?
their distribution
their temperature
their density
their motion

The average temperature of the typical dark dust cloud is about
100 K

When an electron in a hydrogen atom changes its spin from the same to the opposite direction as the proton, it
emits a radio wave photon.

A reflection nebula appears blue because it scatters the _____ light of the stars near it.
blue or shorter wavelength

Of the following telescopes, the one best suited to observing dark dust clouds is
radio telescope.

Why do stars tend to form in groups?
A large interstellar cloud fragments into smaller clouds that eventually form stars.

What temperature is required to initiate nuclear fusion in a stellar core?
10,000,000 K

Which of the following best describes what happens to a one-solar-mass star when it reaches the main sequence?
Its temperature, luminosity, and radius remain essentially constant for the next 10 billion years.

A newly formed protostar will radiate primarily at which wavelength?
infrared

During the T-Tauri phase of a protostar, it
may develop very strong winds.

What is the main-sequence (hydrogen core-burning) lifetime for stars like the Sun?
10 billion years

Why does a star like the Sun leave the main sequence?
It runs out of hydrogen fuel for nuclear fusion in its core.

A star (no matter what its mass) spends most of its life
as a main-sequence star.

What was most surprising about SN1987A?
The parent star was a blue supergiant, much like Deneb or Rigel.

What made supernova 1987A so useful to study?
In the Large Magellanic Cloud, we already knew its distance.
Its progenitor had been observed previously.
It occurred after new telescopes, such as Hubble, could observe it very closely.
We saw direct evidence of nickel to iron decay in its light curve.

Hydrogen-shell burning proceeds increasingly faster due to which of the following?
heat released from the core’s contraction

How do stars on the horizontal branch generate energy?
Fusion of helium to carbon in the core

As a low-mass main-sequence star runs out of fuel in its core, it actually becomes brighter. How is this possible?
The outer layers expand due to the faster rate of fusion in a shell around the dead core.

When a low mass star first runs short of hydrogen in its core, it becomes brighter because
the core contracts, raising the temperature and extending the hydrogen burning shell outward.

A star is on the horizontal branch of the H-R diagram. Which statement is true?
It is burning both hydrogen and helium.

The helium flash converts helium nuclei into
carbon

Can a star become a red giant more than once?
yes, before and after the helium flash

A white dwarf has the mass of the Sun and the volume of
Earth.

Which of these is true of planetary nebulae?
They are ejected envelopes surrounding a highly evolved low-mass star.

A(n) ________ represents a relatively peaceful mass loss as a red giant becomes a white dwarf.
planetary nebula

A surface explosion on a white dwarf, caused by falling matter from the atmosphere of its binary companion, creates what kind of object?
nova

Which of these evolutionary paths is the fate of our Sun?
planetary nebula

Of the elements in your body, the only one not formed in stars is
hydrogen

A 20-solar-mass star will stay on the main sequence for 10 million years, yet its iron core can exist for only a
day

An iron core cannot support a star because
iron cannot fuse with other nuclei to produce energy.

The Chandrasekhar limit is
the upper-mass limit for a white dwarf.

the upper-mass limit for a white dwarf.
Type l Supernova

You would expect to find the least number of young O,B stars in the
halo

There is evidence that a supermassive black hole is at the center of the Milky Way based upon
The orbits of stars very close to the center.

In which of the basic regions of the Galaxy is the Sun located?
galactic disk

In structure, our Milky Way is most similar to
M31, the Andromeda Galaxy.

All RR Lyrae stars have about the same
luminosity of about 100 Suns.

The first attempt to map the Galaxy via star counts was done by
William Herschel in the late eighteenth century.

A star in the instability strip of the H-R diagram would
vary in both temperature and radius.

For finding the distances to globular clusters, Harlow Shapley used
RR Lyrae variables

Which is the correct description of the Sun’s location within the Milky Way?
in the disc and about one-half a galactic radius from the center

What is one of the differences between Cepheids and RR Lyrae variables?
The RR Lyrae stars have much shorter periods than Cepheids.

The orbits of Population II stars have been compared to
comets around the Sun.

The Galactic Year is the time for our solar system to orbit the Galaxy; it is about
225 Million years

Detailed measurements of the disk and central bulge region of our Galaxy suggest our Milky Way is a
barred spiral galaxy.

In our location in the Milky Way, the galactic disk is only about ________ ly thick.
1000

Virtually the entire disk of the Galaxy has been mapped using the _____ wavelength.
21-cm

In the formation of our Galaxy, the ________ formed first.
globular clusters

Which sequence of formation is most likely to be correct, oldest to youngest?
globular clusters, open clusters, OB associations

Density waves may explain
the spiral arm structure of the Galaxy.

The flattest of the ellipticals are class
E7.

Which property is common to spiral galaxies?
ongoing star formation and emission nebula in the arms

The astronomer who originally classified galaxies into S, E, and Irr was
Edwin Hubble.

The Milky Way is considered to be an intermediately wound, barred spiral, which would be type ________ according to Hubble.
SBb

The greatest variation in size, mass, and luminosity occurs in
elliptical galaxies.

The most luminous objects known in the universe are
quasars

The spiral arms are blue from the prescence of Population _____ stars in them.
I

Which of the following galaxy types is the most numerous in our Local Group of galaxies?
small ellipticals and irregulars

The Tully-Fisher relation uses the close correlation between the rotational speed of a spiral galaxy and its luminosity as a distance indicator. Why does this correlation exist?
The greater the mass of a galaxy, the faster it spins, and the more mass there is to give off light.

Which of these standard candles has been used to determine distances to the most distant galaxies?
Type I supernovae

What is true of the Local Group?
The Andromeda galaxy (M31), and the Milky Way are the two largest galaxies.

About how many galaxies are presently known in our Local Group?
55

What are Type I supernovae used for?
Standard candles for determining distances to other galaxies.

Most of the galaxies in the Local Group are
small ellipticals like the companions to M31 in Andromeda.

Intermediate between E7 and Sa galaxies, _____ have a disk but no gas or dust.
S0

According to Hubble’s law, as the distance to galaxies ________, the ________ increases.
increases; apparent recessional velocity

Which of the following is NOT an implication of Hubble’s law?
The Milky Way Galaxy is at the center of the Universe

What is observed that connects radio emissions in the galactic nucleus with the emissions in the halo or radio lobes?
There is a jet of matter coming out of the nucleus, which often points toward the lobes.

What is the best explanation of the differences between a lobe radio galaxy and a core-dominated radio galaxy?
There is no real difference. When we look at core-dominated radio galaxies, we are looking at the galaxy through one of its lobes and along one of the jets.

The nearest lobe radio galaxy to our Milky Way is
Centaurus A.

The key to finding quasar’s distances was
the huge red shifts of the hydrogen lines in 3C273.

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