Astro homework Flashcards
A lightyear is
the distance that light travels in one year
Which of the following is most abundant in the Universe?
Helium
When an atom has lost one or more electrons, it is said to be:
ionized
Newton showed that to change the direction in which an object is moving, one needs to apply:
a force
As astronomers have learned more about the structure of the Sun, they have found that it
is made entirely of hot gas
The most common element in the Sun is
hydrogen
You are out on the beach, enjoying the warm sunshine with friends. As you glance up at the Sun, the part of the Sun that you can see directly is called its:
photosphere
The antimatter version of an electron is called a
positron
Which magnitude looks the brightest in the sky?
a star with magnitude -1
Which of the following characteristics of a single star (one that moves through space alone) is it difficult to measure directly?
its mass
I am measuring the spectrum of the stars in a spectroscopic binary system. When one of the stars is moving toward the Earth in its orbit, we observe
that the lines in its spectrum show a blue-shift
For what type of star can astronomers measure the diameter with relative ease?
eclipsing binary stars
Measurements show a certain star has a very high luminosity (100,000 x the Sun’s) while its temperature is quite cool (3500o K). How can this be?
it must be quite large in size
Where on the H-R Diagram would we find stars that look red when seen through a telescope?
only on the right side of the diagram and never on the left.
Astronomers use the term interstellar medium to refer to:
gas and dust that lies between stars
An HII region is
a zone around a hot star where hydrogen atoms are ionized
If you want to find stars that are just being born, where are the best places to search?
in giant molecular clouds
A star whose temperature is increasing but whose luminosity is roughly constant moves in what direction on the H-R diagram?
to the left
Which of the following types of stars will spend the longest time (the greatest number of years) on the main sequence?
K
A type of star cluster that contains mostly very old stars is
a globular star cluster
The event in the life of a star that begins its expansion into a giant is
almost all the hydrogen in its core that was hot enough for fusion has been turned into helium
As a cluster of stars begins to age, which type of star in the cluster will move off the main sequence of the H-R diagram first?
the O and B type stars
what will happen after the life of a star with a mass like the Sun?
as the star is dying, a considerable part of its mass will be lost into space.
When a single star with a mass equal to the Sun dies, it will become a
white dwarf
The most stable (tightly bound) atomic nucleus in the universe is:
iron
In a supernova like SN1987A, once the crisis of iron fusion has begun, roughly how long does it take the star’s core to collapse?
less than a second
If you are in a freely falling elevator near the top of a tall building, as the elevator falls, your weight would be:
equal to zero – you would be weightless
To predict whether a star will ultimately become a black hole, what is the key property of the star we should look at?
mass
The region around a black hole where everything is trapped, and nothing can get out to interact with the rest of the universe, is called
an event horizon
Wearing a very accurate watch, you volunteer to go on a mission to a black hole in a spaceship that has powerful rockets. You are able to orbit the black hole and stay a little distance outside of the event horizon. Compared to watches on Earth, your watch near the black hole will run:
more slowly
Objects orbiting around the center of the Milky Way obey Kepler’s 3rd Law. This means that:
a cloud of gas or star that is further from the center will generally take more time to orbit
For the Milky Way, compared to the sun stars in the inner central bulge have:
slower Galactic orbital velocities
Order the following regions of the Galaxy from youngest mean stellar age to oldest:
thin disk, thick disk, halo
Order the following in order of total mass:
thin disk, halo, thick disk
If I want to find a sizeable collection of Population II stars in the Milky Way Galaxy, where would be a good place to look?
in a globular cluster high above the Galaxy’s disk
Which type of galaxy is observed to contain mostly older stars?
giant elliptical
Which is one reason that the typical galaxy’s mass-to-light ratio (in units of the Sun’s mass over the Sun’s luminosity) generally greater than 1?
galaxies contain many more stars that shine much less brightly than the Sun
What method would astronomers use to find the distance to a galaxy so far away that individual stars are impossible to make out (resolve)?
finding the redshift and using Hubble’s Law
According to our current understanding, giant elliptical galaxies form:
by the merger (or swallowing) of a number of smaller galaxies in a cluster of galaxies
The Andromeda Galaxy (our nearest spiral neighbor) has spectral lines that show a blue shift. From this we may conclude that:
this particular nearby galaxy is moving toward us
According to Hubble’s Law, if two galaxies are not part of our Local Group, and galaxy B is three times farther away from us as Galaxy A, then Galaxy B will
move away from us three times faster than A
If the Hubble Constant is currently 68 km/s/Mpc and a distant galaxy is 1 Gpc away, approximately what is its redshift?
.22
When we determine the age of the universe using the Hubble Time, what important simplifying assumption goes into our calculations?
that the expansion of the universe has been happening at the same rate – neither speeding up or slowing down
The Hubble constant is measured to be 68 km/s/Mpc at time A.
At another point in time, B, it was measured to be 90 km/s/Mpc.
At another point in time, C, the Hubble Time was measured to be 18 billion years.
Order the age of the Universe at times A, B, and C from LEAST to MOST.
Time B, Time A, Time C
Based on many surveys of the average density of matter in the universe (regular matter and dark matter), astronomers now conclude that the average density of the universe is
less than the critical density
Today, we believe that only a small number of elements were actually formed during the Big Bang. what are they(3)
helium, lithium, hydrogen
After the Big Bang, in order for the universe to become transparent to light and other electro-magnetic radiation, what had to happen?
free electrons needed to bind to nuclei
The rich galaxy cluster that is closest to our Local Group of galaxies is the
Virgo Cluster
When astronomers say that the groups of galaxies are distributed isotropically, they mean that
the way galaxies are arranged in space looks the same in all directions
