Astronomy Homework

Early in the last century, astronomers discovered that most galaxies are moving away from our own, by observing that their light is redshifted. What is the important implications of this discovery?
The universe is expanding, providing evidence that it began with a big bang.

What is the origin of the cosmic background radiation (CBR)?
The temperature of the CBR is much lower than when it was emitted.
The CBR consists of Microwave wavelengths, as would be expected if the highly energetic wavelengths of light from the early universe were stretched one thousandfold as the universe expanded.
the CBR has a Planck distribution. This means it came from the “black body” predicted by the Big Bang Theory.

Order the following historical ideas of “everything” (the universe) from the earliest to most recently developed
-The Milky Way Galaxy,
-All of Spacetime created by the Big Bang, “Island Universes”, or galaxies, including our own
Earth, with the stars and planets on concentrated shells
The Solar system, with stars on a shell ouside
(Early history)
-Earth, with the stars and planets on concentric shells
– The solar system, with stars on a shell outside
– The Milky Way Galaxy
-“Island Universe”, or galaxies, including our own
– All of spacetime created in the Big Bang.

What does the cosmological redshift of a distant galaxy tell astronomers about that galaxy?
its recession speed

Order the following methods for distance measurement from shortest distance to long distance.
parallax
cepheid variables
galactic redshifts
radar
type 1a supernovae
main-sequence fitting
Radar
Parallax
Main-Sequence fitting
Cepheid Variables
Type 1a Supernovae
Galactic redshifts

True or False:

The relative abundance of protons and neutrons right after the Big Bang is consistent with the subsequent created of more hydrogen than helium.

true

What element was synthesized in the Big Bang?
Hydrogen

What can we infer from the fact that nearly all galaxies are moving away from us?
the universe is expanding

Some galaxies have regions that are relatively blue in color, while other regions appear redder. aside from color, what can you say about the differences between these regions?
Blue regions have hotter stars.
the blue regions have more young, bright stars.

What is the evidence that most galaxies are composed largely of dark matter?
Objects far from the centers of spiral galaxies orbit too quickly for the amount of luminous matter present.
Hot gas in elliptical galaxies doesn’t escape as it would with just luminous matter.

True or False:
galaxy interactions are likely to result in the formation of hot new stars.
true

True or False:
Galaxy collisions cause the disk of a spiral galaxy to become warped and the spiral arms to widen.
true

true or false:
Elliptical galaxies that we see today may one have been spirals that lost their original shapes after many interactions with other galaxies.
true

Spiral arms are delineated by luminous, massive stars because:
galactic halomassive stars do not live long enough to escape the spiral arms

Where is dark mater typically found in a spiral galaxy?
galactic halo

What do astronomers mean when they speak of a “standard candle?”
an object with a known luminosity that is visible over large distances

Why are globular clusters so useful as standard candles in determining the size of the galaxy?
they reside throughout a halo surrounding the galaxy.
they contain RR Lyrae variables
they reside in and around the galactic plane.

Where are the oldest stars in the milky way located?
globular clusters

What does the abundance of a star’s massive elements tell us about the age of the star?
stars with the highest concentration of the heaviest elements are younger stars that have been born after many earlier generations of stars have seeded the interstellar medium with those elements.

To observers in Earth’s Southern Hemisphere, the Large and Small Magellanic Clouds look like detached pieces of the Milky Way. What are these clouds and why is it not surprising that they look so much like pieces of the Milky Way?
irregular dwarf galaxies that occasionally crash through the disk of the Milky Way.

Place these objects in order based on their mass. hint: assume the Large Magellanic Cloud has a mass of approximately 10^10 solar masses.

Globular cluster
large magellanic cloud
open cluster
sagittarious A

open cluster
globular cluster
sagittarius A
large magellanic cloud

true or false:
Dark matter is a solved mystery.
false
dark matter remains an unsolved mystery.

true or false:
according to Newton’s laws, if mass if concentrated in the center of a galaxy, stars closer to the center should move faster in their orbits than those farther away.
true

Each of the following items existed at one time, and some exist today in our Milky Way Galaxy. Rank them on their expected abundance of massive elements.(lowest – highest)

Interstellar cloud with primordial matter
star in inner part of the disk
star in a globular cluster
star in the outer edge of the disk

(lowest)
Interstellar cloud with primordial matter
star in globular cluster
star in the outer edge of the disk
star in the inner part of the disk
(highest)

What piece of observational evidence suggest that Einstein’s cosmological constant (a repulsive force) may be needed to explain the historical expansion of the universe?
Detailed overvations of the structure of the Cosmic Background Radiation (CBR) favor a cosmological constant.
the redshifts of Type I supernovae are too small for their distances.
Mass measurements in galaxies and cluster suggest a repulsive force.

If a circle is drawn on a spherical surface, will the circumference be greater than, less than, or equal to 2 Pi?
less than

If a triangle is draw on a spherical curface, will the sum of the interior angles be greater than, less than, or equal to 180 degrees?
greater than

Do astronomers believe we live in a closed, flat, or open universe?
flat

The critical mass density of a non-accelerating universe determines:
the ultimate fate of the universe

Order these events in the history of the universe (early-Late)
-First stars form
-Protons and neutrons combine to form light elements
-Quantum theory of gravity is necessary
-Quarks combine to form protons and neutrons
-universe becomes transparent to photons
-universe undergoes exponential inflation
-Quantum theory of gravity is necessary
-universe undergoes exponential inflation
-Quarks combine to form protons and neutrons
-Protons and neutrons combine to form light elements
-universe becomes transparent to photons
-First stars

What explanation do cosmologists currently invoke to explain the horizon and flatness problems?
inflation theory

In the first 100 seconds, the universe contained:
photons, electrons, and positrons

As clumps containing dark matter and normal collapse, they heat up. when a clump collapses to about half its maximum size, the increased thermal motion of particles tends to inhibit further collapse. Whereas normal matter can overcome this effect and continue to collapse, dark matter cannot. What is the cause for this difference?
dark matter particles interact only weakly and have no way to lose energy quickly.

Imagine some galaxies in the universe are composed mostly of dark matter with relatively few stars or other luminous normal matter. If this were true, how might we learn of the existence of such galaxies?
the dark matter would act as a gravitational lens for background galaxies.

how are the processes of star formation (as studied earlier) and galaxy formation similar?
Initial mass distributions are not uniform.
angular momentum drives disk formation.
gravity collapses density variations.

What is the origin of large-scale structure?
Primordial dark matter fluctuations collapses under their own gravity

Astronomers believe that cold dark matter is composed of:
axions or photinos

what are the largest structures in the universe?
superclusters of galaxies

Approximately, when do scientists believe life first appeared on Earth?
3.5 billion years ago

If we should eventually find life on Europea, what would this tell you about the probability of finding life on worlds around other stars?
it would be highly probably that life is common throughout the galaxy.

Order the following variables from the Drake Equation according to the certainty with which astronomers know their value.
(most certain – least certain)

-Fraction of worlds where life actually arises
-fraction of worlds with life that develop into a technological advanced civilization
– Fraction of stars with planetary systems
-Likelihood that each civilization still exists today
– Number of moons and planets capable of supporting life
– Stars in our galaxy

-stars in our galaxy
-fraction of stars with planetary systems
-number of moons and planets capable of supporting life
-fraction of worlds where life actually arises
-fraction of worlds with like that develop into a technologically advanced civilization
-likelihood that each civilization still exists today

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