The Universe Essay, Research Paper
Student’s Name: Paul Blanton
The Universe
Summary : 100% 5 correct out of the 5 marked for grading
1. What is the composition of the Sun’s surface?
Your Answer: 94% hydrogen, 5.9% helium, .1% other
The Sun’s surface is called the photosphere and it is made up (by number of atoms) of about 94.0% hydrogen and 5.9% helium, with only traces of the heavier elements making up the other 0.1%
2. State the two primary motions that the Sun is undergoing.
Your Answer: It rotates on its axis, and it revolves around the center of the Milky Way Galaxy.
The Sun’s equatorial region rotates about its own axis every 25 Earth days, while the polar regions take slightly longer. The Sun also revolves about the center of the Milky Way Galaxy with a period of one revolution every 250 million years.
3. What are sunspots.
Your Answer:asdf
Sunspots are patches on the surface of the Sun that are cooler than the surrounding region by several hundred degrees. They, therefore, appear as dark spots on the Sun’s hot surface, hence their name. They usually last for several days and sometimes up to several weeks. Sunspots are thousands of miles in width and are related to changes in the Sun’s magnetic field. Sunspots occur in greater numbers on the Sun’s surface in a regular 11-year cycle.
4. What is the celestial sphere?
Your Answer: Imaginary transparent that surrounds the Earth which planets can be positioned.
The celestial sphere is a huge, imaginary, transparent sphere that completely surrounds Earth and on which the observable celestial objects that appear as part of the night sky can be positioned. This sphere undergoes an apparent rotation, as seen by an observer located on Earth’s surface, such that it accounts for the motions of all of the “fixed stars.” The Sun, Moon, and planets move across the surface of the celestial sphere with respect to the fixed stars along a general path called the ecliptic. An observer on Earth’s surface can only see half the celestial sphere at one time. It appears as a large, transparent, overhead dome moving westward, but this apparent motion is really caused by the motion of Earth as it rotates eastward.
5. What is the zodiac?
Your Answer: a section which follows the path of the sun on the celestial sphere.
The zodiac is a section extending around the celestial sphere 8. above and 8. below the apparent path of the Sun across the sphere. This path is called the ecliptic. The zodiac is divided into 12 nearly equal sections, each of which is about 30. wide and 16. high. Each section has its apex at the Sun and extends outward to infinity. The names of these sections, often called the signs of the zodiac, are taken from the predominant constellation that can be seen in that region of the sky.
6. Define the unit of length called the parsec.
Your Answer: Distance to a star when the star s parallel is one second of arc.
One parsec is the distance to a star when that star exhibits a parallax angle of one second of arc. One parsec is equal to 3.26 light-years or 206,265 astronomical units. (See Figure 18.8 in the textbook for details on parallax measurement and the distance unit, the parsec.)
7. What is meant by the absolute magnitude of a star?
Your Answer: The apparent magnitude of a star if it were moved to ten parsecs from Earth.
The absolute magnitude is defined as the apparent magnitude that a star would have if it were moved (in our imagination) to a location exactly 10 parsecs from Earth. Thus the absolute magnitude can be used to compare the true brightnesses of the stars. When we observe stars in their actual locations from Earth, their distances from us are primary factors in determining how bright they appear to be. The actual brightness that we observe when viewing a star from Earth is called the apparent magnitude of that star.
8. What is a Hertzsprung-Russell diagram?
Your Answer: A plot of absolute magnitudes of stars.
A Hertzsprung-Russell, or H-R diagram is a plot of the absolute magnitudes of stars as a function of their surface temperatures. On an H-R diagram, different types of stars, such as main sequence stars, red giants, and white dwarfs, are located in well defined areas, which makes the diagram useful in assigning characteristics to stars for which we know only the absolute magnitude and/or surface temperature.
9. What are Cepheid variables?
Your Answer: Stars in which their absolute magnitude varies.
Cepheid variables are stars that exhibit a periodic variation in their absolute magnitude or brightnesses. A linear relationship has been discovered between the length of these periods and the absolute magnitudes of the stars, so we need only measure the time between brightness maxima to estimate the absolute magnitude of a given star. Then using the inverse square law of intensity we can calculate the distance to this star. This is one of the best methods astronomers have for finding the distance to faraway stars and the galaxies that they inhabit.
10. How are galaxies classified?
Your Answer: By their appearance to an observer on Earth.
Galaxies are classified by their appearance to an observer on Earth. This determination is usually made after studying photographs of the galaxies taken by our largest telescopes.
11. What are the three main classifications of galaxies?
Your Answer: Elliptical, spiral, and irregular.
Galaxies are classified as either elliptical or spiral, depending on their appearance as seen from Earth. Any galaxies that do not fit into these two main categories are simply called irregular galaxies.
12. Which type of galaxy is most abundant?
Your Answer: Most are spiral galaxies
Of the brighter galaxies observed from Earth, over 75% are of the spiral type, but in any given volume of space there are more elliptical galaxies than spirals. This is the case because elliptical galaxies are made up of older stars that are generally dimmer than the young stars that predominate in spiral galaxies. This makes the spiral galaxies easier to see at large distances. The third type, irregular galaxies, appear to make up only about 3% of all known galaxies.
13. What are the principal phases in the life cycle of a star?
Your Answer: Begin as a cloud of gas called main sequence stars, then depending on their size, they enter white dwarf, neutron, or black hole stage.
Stars begin their lives as large clouds of gas and dust that collect under the pull of gravity into main sequence stars, during which phase they produce energy from the fusion of hydrogen in their cores. When the hydrogen becomes depleted, they evolve into their red giant phase where helium is the main core fuel. When the helium in the core also gives out, stars end their lives in one of three final states, depending on their masses at this point in their lives. These final states are white dwarf stars, neutron stars, and black holes.
14. What are the physical dimensions of the Milky Way Galaxy?
Your Answer: 100,000 light-years in diameter and 2,000 light-years thick.
The Milky Way is 100,000 light-years in diameter and 2,000 light-years in thickness in the region where our solar system is found. There is also a much thicker central bulge (10,000 ly) surrounding its center of rotation. The Milky Way contains about 100 billion individual stars.
15. What is a black hole?
Your Answer: a collapsed star with strong gravitational pull.
A black hole is believed to be a collapsed star with a gravitational field so strong that nothing, not even light, can escape from it. Black holes are the final stage in the life cycles of the most massive stars.
16. What are Seyfert galaxies?
Your Answer: They have bright centers and tend to give off high levels of radio emissions.
Seyfert galaxies are galaxies that exhibit very bright centers and whose spectra show broad emission lines. They tend to give off large amounts of radio emissions from their cores, but they look like normal spiral galaxies through an optical telescope.
17. What are superclusters?
Your Answer: Large clusters made of individual clusters of galaxies.
Superclusters are huge clusters made up of many individual clusters of galaxies lumped together. They vary from 50 to 300 million ly in diameter and contain masses that are estimated to be greater than 1015 solar masses.
18. What is the Hubble constant?
Your Answer: Constant of proportionality in Hubble s law which relates to galaxies distance from Earth.
The Hubble constant is the constant of proportionality (H) in Hubble’s law (v = H d), which relates the speed of recession (v) for remote galaxies to their distances from Earth (d). The present value for H is believed to be in the range of 50 to 100 km/s/106 pc.
19. With respect to a black hole, what is a singularity?
Your Answer: The center of a black hole.
A singularity is the center of a black hole. It is a single point to which a very massive star has been reduced by a process called gravitational collapse. Its properties include a very large concentrated mass, an infinite density, and a radius that is actually associated with its event horizon, not the singularity itself.
20. What is an event horizon?
Your Answer: The boundary surrounding a black hole.
An event horizon is the boundary surrounding a black hole. Once inside the event horizon, no physical matter or radiation, not even light, can ever escape, hence the name black hole.
21. The lifetime of a star on the main sequence
a. is infinite.
b. is inversely proportional to the star’s total mass.
c. cannot be determined.
d. depends on where it is located within a galaxy. Correct
22. The rotational period of the equatorial region of the Sun is about 25 Earth days. Astronomers on Earth have determined this by
a. observing the east-to-west motion of sunspots. Correct
b. using the Doppler shift of spectral lines emitted from the center of the Sun’s photosphere.
c. measuring the motion of the solar wind.
d. observing differences in the Sun’s surface temperature.
23. A Hertzsprung-Russell diagram, or H-R diagram, shows the relationship between the
a. absolute magnitude of a star and its velocity.
b. velocity of a star and its distance from Earth.
c. relative size of a star and its rotational speed.
d. luminosity of a star and its temperature. Correct
24. Hubble classified the galaxies into three general types. These types are
a. ellipticals, whirlpools, and sphericals.
b. sphericals, spirals, regulars.
c. ellipticals, spirals, irregulars. Correct
d. near, moderate, far.
25. A black hole is best described as
a. an empty volume of space.
b. an invisible hole in the universe.
c. a singularity surrounded by an event horizon. Correct
d. the central core of a quasar that is invisible.
26. Describe two surface features of the Sun that can be seen from Earth through a properly shielded telescope.
Your Answer: Sunspots dark spots on the sun which are strong magnetic fields. Prominences great eruptions at the edge of the sun s surface.
The two most distinct features of the Sun’s surface that can be seen through a properly shielded telescope are:
sunspots – dark regions on the Sun’s surface characteristic of strong magnetic activity and showing cooler temperatures than the surrounding areas.
prominences – great eruptions at the edge of the Sun that are connected with violent storms in the chromosphere.
27. What process produces the energy necessary to make our Sun shine? Explain briefly how this process works.
Your Answer: The Sun shines because of the fusion reactions that take place in its core.
The Sun shines, that it emits radiant energy into space, because of heat produced in fusion reactions taking place deep in the core of the Sun. This fusion process converts hydrogen into helium by taking four protons (hydrogen nuclei), and combining them into a helium-4 nucleus in a process called the proton-proton chain.
28. Describe the celestial sphere, and tell how it is oriented with respect to Earth.
Your Answer: Imaginary transparent that surrounds the Earth which planets can be positioned.
A celestial sphere is a huge, imaginary, transparent globe that surrounds Earth upon which all of the fixed stars are placed and upon which the positions of the Sun, Moon, and planets can also be assigned. If this imaginary sphere is allowed to rotate, it can be used to simulate the motion of the stars and planets as they appear to move around Earth each day. It must be remembered that it is really the Earth’s rotational motion on its own axis that causes this apparent motion.
The celestial equator lies directly above Earth’s equator and the north celestial pole and south celestial pole are positioned directly above Earth’s North and South poles, respectively.
29. What are constellations, and how have they acquired their names?
Your Answer: Patterns of stars that are named after the shapes they represent.
There are 88 constellations that are composed of certain patterns of stars as pictured from Earth. These patterns cover well-defined areas of the sky, and any one star can only be part of one of these established groups. The constellations are named after figures or creatures as seen in the sky by the early Babylonians and Greeks and sometimes carry the names of ancient gods and mythical animals.
30. Where does the red giant phase come in the overall life cycle of a star?
Your Answer: After the core has burned out, the surface will cool and turn red.
After a star has been in its main sequence phase long enough to use up all of the hydrogen fuel in its core, the star’s core will collapse and its outer layers will expand and cool, producing a very large, reddish colored star known as a red giant. During the red giant phase, helium is consumed in the hot, high pressure core of the star until all of the helium is used up, at which time the star again becomes unstable and evolves further into a white dwarf, a neutron star, or a black hole.
31. List the spectral types into which stars are grouped, and state into which type the Sun has been classified.
Your Answer: hottest to coolest:OBAFGKM, sun is a G star.
The spectral classes into which stars are classified by their surface temperatures from hottest to coolest are; O, B, A, F, G, K, M. Our Sun has a relatively cool surface, about 6000 K, and is classified as a G type star.
32. What is a supernova?
Your Answer: Explosion which occurs when a core of a star collapses.
A supernova is a tremendous explosive event that occurs when the core of a massive main sequence star collapses with such energy that the star may completely destroy itself. This may occur after the nuclear fusion reactions in the core of the star have used up all available fuel.
33. Describe a simplified H-R diagram, and indicate the location of the following: main-sequence stars, red giants, and white dwarfs. (Draw a simple diagram if you wish.)
Your Answer: The diagram plots the absolute magnitude of stars.
An H-R diagram is a plot of the absolute magnitudes of many stars as a function of their spectral classes (this is essentially the same thing as their surface temperatures). Such a plot shows all of the main sequence stars in a diagonal pattern, with the heaviest of them at the upper left corner and the less massive ones in the lower right-hand corner of the diagram. Red giant stars are plotted above and to the right of the main sequence, and white dwarf stars are below and near the center of the main sequence plot. See Figure 18.11 in the textbook for a pictorial representation of an H-R diagram.
34. Explain how galaxies are classified, and give the names for the three main classes of galaxies.
Your Answer: They are classified by how they look from the Earth. Three classes are elliptical, spiral, and irregular.
Galaxies are classified by the way that they appear as seen from Earth. Galaxies that have a clearly spherical or flattened spherical shape are called elliptical galaxies, and those showing a tight or loose spiral structure are called spiral galaxies. Any galaxies that cannot be classified as elliptical or spiral are designated as irregular galaxies.
35. What is the cosmological redshift, and what does it suggest about the origin of the universe?
Your Answer: A shift in galaxies toward the low frequency. From this we can tell the universe is expanding and began with an explosion, the Big Bang.
The cosmological redshift is a shift in the spectrum lines of galaxies toward the low-frequency (red) end of the electromagnetic spectrum. It is believed that this shift in spectrum lines is the result of the overall expansion of the universe. This redshift along with the discovery of the 3-K cosmic background radiation and the observed mass ratio of hydrogen to helium throughout the universe all point to a model in which the universe was created in a gigantic explosion, the Big Bang, and we now see the entire
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