Astro 101 RQ Chapter 1
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Michigan State University *
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Astronomy
Date
Feb 20, 2024
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3
Uploaded by ConstableRain9306
Rachel Goodin
ASTRO 101
RQ Chapter 1
1/12/2024
1.
Briefly describe the major levels of structure (such as planet, star, galaxy) in the
universe.
A planet can be described as a large, round astronomical body that is neither a star nor its
remnant. Earth is a planet in our solar system, which consists of the Sun, the planets and their
respective moons, and countless other smaller objects that include rocky asteroids and icy
comets. The Sun in our solar system is actually a star, which is a large, glowing ball of gas that
produces heat and light through nuclear fusion. A galaxy is a great island of stars in space that
are all held together by gravity and orbiting a common center. Our galaxy, as previously
described, is called the Milky Way Galaxy, which exists as a relatively large galaxy and contains
more than 100 billion stars and countless more orbiting planets. The Milky Way Galaxy is a little
over halfway from the galactic center to the edge of the galactic disk. Galaxies can also exist in
galaxy clusters, such as the one called the “Local Group” that our own Milky Way exists within.
Together, all of these structures make up the total of the universe.
2.
Define
astronomical unit
and
light-year
.
One astronomical unit (AU) is a measurement of distance used to describe specifically the
average distance of the Earth from the Sun, which is approximately 150 million kilometers, or 93
million miles. Astronomical units are used commonly to describe distances within our solar
system. A light-year, though often mistaken for a unit of time, is actually a unit of distance. A
light-year describes the distance that light can travel in one year, which is approximately 10
trillion kilometers or 6 trillion miles. Light-years are generally used to describe the distances of
stars and galaxies.
3.
Explain the statement
“The farther away we look in distance, the further back we
look in time.”
This statement refers to the general idea that light takes time to travel through space. Thus,
since light takes time to reach earth, we are essentially looking back in time when viewing
anything a distance from the Earth. For example, the Andromeda Galaxy is about 2.5 million
light-years away, which means we see it as it looked about 2.5 million years ago.
4.
What do we mean by the observable universe? Is it the same thing as the entire
universe?
The observable universe refers to the portion of the entire universe that can be seen from Earth
in principle. The observable universe is therefore only a tiny fraction of the entire universe,
hence meaning that they are not the same thing.
5.
6.
What do we mean when we say that the universe is expanding, and how does
expansion lead to the idea of the Big Bang and our current estimate of the age of
the universe?
When we say that the universe is expanding, this means that the average distance between
galaxies is increasing. This implies that, at some point long ago in the past, the galaxies must
have been much closer together. It is generally believed that the universe is about 14 billion
years old, and thus the Big Bang represents the beginning point of the universe and the start of
universe expansion, at which the galaxies were at their closest average distances relative to
one another.
7.
In what sense are we “star stuff”?
The Earth and the things that we know of on it are primarily made up of elements such as
carbon, nitrogen, oxygen, and iron. Since the early universe has been proved to made of only
the simplest chemical elements such as hydrogen and helium, it is believed that these other
earthly elements originated from processes of nuclear fusion that involve both the creations and
explosive destructions of stars. Thus, most of the material from which we and our planet are
made was created inside stars that lived and died before the birth of our Sun.
8.
Use the cosmic calendar to describe how the human race fits into the scale of
time.
According to the cosmic calendar, the Big Bang occurred at the first instant of January 1 and
the present is the stroke of midnight on December 31. The earth and our solar system would
have been formed in early September, with flourishing life on earth occurring by late September.
Dinosaurs went extinct on December 30th, and early hominids evolved at about 9pm on
December 31st. Modern humans evolved at 11:58pm on this same day, with Kepler and Galileo
having proved that the Earth orbits the Sun only one second ago from the present.
9.
Briefly explain Earth’s daily rotation and annual orbit, defining the terms ecliptic
plane and axis tilt.
The Earth rotates once each day (24 hours) around its axis at about 1000 km/hr, and its annual
orbit around the Sun is completed once per year (365 days) at over 100,000 km/hr. However,
the speed of rotation or revolution is dependent upon your location on the planet, so these
speeds are in fact relative. The ecliptic plane refers to the plane of Earth’s orbit around the Sun,
while the axis tilt is the amount by which a planet’s axis is tilted with respect to a line
perpendicular to the ecliptic plane. Earth’s axis is tilted by 23.5
o
from a line perpendicular to the
ecliptic plane.
10. Briefly describe our solar system’s location and motion within the Milky Way
Galaxy.
Our solar system is located approximately 27,000 light-years away from the galactic center of
the Milky Way. We complete one full orbit around this galactic center once every 230 million
years. The galaxy’s rotation carries us around the galactic center at about 800,000 km/hr.
11. Why do scientists suspect that most of our galaxy’s mass consists of dark
matter? Briefly describe the mystery of dark matter and dark energy.
In learning how mass is distributed throughout the galaxy by measuring different star orbit
speeds relative to the galactic center orbit, we find that most of the mass of the galaxy seems to
be located outside of the visible galactic disk, yet this matter is completely invisible to any of our
telescopes. We therefore know very little about the nature of this matter, which we refer to as
dark matter. Studies suggest that other galaxies are also made up of mostly dark matter, and
that this dark matter must be the dominant source of gravity that has led to the formation of
galaxies, clusters, and superclusters. Even less is known about dark energy, which makes up
the majority of the total energy content in the universe. Astronomers first recognized dark
energy when they discovered that the expansion of the universe is actually getting faster with
time.
12. What key observations lead us to conclude that the universe is expanding? Use
the raisin cake model to explain how these observations imply expansion.
One key observation in leading us to conclude that the universe is expanding is that virtually
every galaxy outside of the Local Group is moving away from us. Additionally, the more distant
the galaxy, the faster it appears to move away from a central cosmic location. This can be
represented with the raisin cake model, which describes the baking of a raisin cake with a
singular raisin as a ‘local’ point. Before baking the cake, this raisin is one centimeter away from
the other raisins. After baking the cake, the cake having risen and expanded in the baking
process, this same raisin is now three centimeters away from the other raisins. Thus, the raisin
cake is an analogy for the ever-expanding universe.
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