Astronomy
1st Edition
ISBN: 9781938168284
Author: Andrew Fraknoi; David Morrison; Sidney C. Wolff
Publisher: OpenStax
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Textbook Question
Chapter 25, Problem 8E
Suppose the Milky Way was a band of light extending only halfway around the sky (that is, in a semicircle). What, then, would you conclude about the Sun’s location in the Galaxy? Give your reasoning.
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For a circular velocity profile of the type (r) = ar¹/9, where a is a constant and r is the radial distance from the centre of a spiral galaxy, find the ratio
K(r)/(r), where K(r) is the epicyclic frequency and 2(r) is the angular velocity. Enter your answer to 2 decimal places.
Our galaxy is approximately 100,000 light years in diameter and 2,000 light years thick through the plane of the galaxy. If we were to compare the ratio of the diameter galaxy and its thickness to the ratio of the diameter of a CD and its thickness (CD has a diameter of 12 cm and thickness of 0.6 mm), what would be the factor differentiating those ratios? Put differently, if the galaxy were scaled down to the diameter of a CD, how many times thicker or thinner would the galaxy be than the CD? (For example if it would be twice as thick, you would answer 2 and if it were twice as thin you would answer 0.5 (aka 1/2))
White Dwarf Size II. The white dwarf, Sirius B, contains 0.98 solar mass, and its density is about 2 x 106 g/cm?. Find the radius of the white dwarf in km to three significant digits. (Hint: Density = mass/volume, and the volume of a
4
sphere is Tr.)
3
km
Compare your answer with the radii of the planets listed in the Table A-10. Which planet is this white dwarf is closely equal to in size?
I Table A-10 I Properties of the Planets
ORBITAL PROPERTIES
Semimajor Axis (a)
Orbital Period (P)
Average Orbital
Velocity (km/s)
Orbital
Inclination
Planet
(AU)
(106 km)
(v)
(days)
Eccentricity
to Ecliptic
Mercury
0.387
57.9
0.241
88.0
47.9
0.206
7.0°
Venus
0.723
108
0.615
224.7
35.0
0.007
3.4°
Earth
1.00
150
1.00
365.3
29.8
0.017
Mars
1.52
228
1.88
687.0
24.1
0.093
1.8°
Jupiter
5.20
779
11.9
4332
13.1
0.049
1.30
Saturn
9.58
1433
29.5
10,759
9.7
0.056
2.5°
30,799
60,190
Uranus
19.23
2877
84.3
6.8
0.044
0.8°
Neptune
* By definition.
30.10
4503
164.8
5.4
0.011
1.8°
PHYSICAL PROPERTIES (Earth = e)…
Chapter 25 Solutions
Astronomy
Ch. 25 - Explain why we see the Milky Way as a faint band...Ch. 25 - Explain where in a spiral galaxy you would expect...Ch. 25 - Describe several characteristics that distinguish...Ch. 25 - Briefly describe the main parts of our Galaxy.Ch. 25 - Describe the evidence indicating that a black hole...Ch. 25 - Explain why the abundances of heavy elements in...Ch. 25 - What will be the long-term future of our Galaxy?Ch. 25 - Suppose the Milky Way was a band of light...Ch. 25 - Suppose somebody proposed that rather than...Ch. 25 - The globular clusters revolve around the Galaxy in...
Ch. 25 - Shapley used the positions of globular clusters to...Ch. 25 - Consider the following five kinds of objects: open...Ch. 25 - The dwarf galaxy in Sagittarius is the one closest...Ch. 25 - Suppose three stars lie in the disk of the Galaxy...Ch. 25 - Why does star formation occur primarily in the...Ch. 25 - Where in the Galaxy would you expect to find Type...Ch. 25 - Suppose that stars evolved without losing...Ch. 25 - Assume that the Sun orbits the center of the...Ch. 25 - The Sun orbits the center of the Galaxy in 225...Ch. 25 - Suppose the Sun orbited a little farther out, but...Ch. 25 - We have said that the Galaxy rotates...Ch. 25 - If our solar system is 4.6 billion years old, how...Ch. 25 - Suppose the average mass of a star in the Galaxy...Ch. 25 - The first clue that the Galaxy contains a lot of...Ch. 25 - The best evidence for a black hole at the center...Ch. 25 - The next step in deciding whether the object in...Ch. 25 - Suppose the Sagittarius dwarf galaxy merges...
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- Suppose three stars lie in the disk of the Galaxy at distances of 20,000 light-years, 25,000 light-years, and 30,000 light-years from the galactic center, and suppose that right now all three are lined up in such a way that it is possible to draw a straight line through them and on to the center of the Galaxy. How will the relative positions of these three stars change with time? Assume that their orbits are all circular and lie in the plane of the disk.arrow_forwardConsider the following data on four stars: Which star would have the largest radius? Which star would have the smallest radius? Which star is the most common in our area of the Galaxy? Which star is the least common?arrow_forwardIndicate whether the following statements are true or false. (Select T-True, F-False. If the first is T and the rest F, enter TFFFFF). A) If we find an O type star in our galaxy, it must be in the disk. B) The nearest large spiral Galaxy, similar in size to the Milky Way, is the Andromeda Galaxy (M31). It is located about 2 million light years from Earth. C) The disk of the Milky Way galaxy is about 100,000 light years in diameter. D) On very large scales, matter in the Universe is distributed in clumps and voids. E) Distances to most stars in the Milky Way are measured by parallax. F) RR Lyrae and Cepheid variable stars are used to measure the distance to nearby galaxies.arrow_forward
- 1. A distant galaxy has an apparent magnitude of 10 and is 4,000 kpc away. What is its absolute magnitude? (Round your answer to at least one decimal place.) The difference in absolute magnitude between two objects viewed from the same distance is related to their fluxes by the flux-magnitude relation. FA/FB= 2.51(MB − MA) 2. How does the absolute magnitude of this galaxy compare to the Milky Way (M = −21)?arrow_forwardFor a circular velocity profile of the type (r) = ar¹ ar1/9, where a is a constant and r is the radial distance from the centre of a spiral galaxy, find the ratio (r)/(r), where (r) is the epicyclic frequency and 2(r) is the angular velocity. Enter your answer to 2 decimal places.arrow_forwardFor each of the following parts, find the most possible type of object by considering the descriptions, and explain your answer. Each part is independent. The possible types are red giant, galaxy, planetary system, planet, dwarf planet, red dwarf, white dwarf, brown dwarf, satellite, asteroid, comet, protostar 2 star, star cluster, galaxy cluster, supercluster, emission nebula, reflection nebula, dark nebula (a) This object moves around the Sun. The nearest distance to the Sun is 0.5 AU, and the farthest distance from the Sun is 1000 AU. (b) This object is red in colour. The density is much lower than that of a star. (c) The mass of this object is the same as that of the Sun. It does not fuse hydrogen. (d) This object moves in a circular orbit about the Sun. Its orbit is between those of Mars and Jupiter. It is round in shape. (e) This object burns hydrogen in a region surrounding its helium core.arrow_forward
- The difference in absolute magnitude between two objects at the same distance is related to their fluxes by the flux-magnitude relation. FA FB = 2.51(MB − MA) A distant galaxy contains a type I classical Cepheid whose period results in an absolute magnitude estimate of −6.3. If this star were placed next to our Sun (M = +4.8) and you observed them both from the same distance, how much more flux would the Cepheid emit than the Sun? FCepheid FSun = If a galaxy contains a supernova that at its brightest has an apparent magnitude of +11, how far away is the galaxy? Assume that the absolute magnitude of the supernova is −18. Hint: Use the magnitude-distance formula: d = 10(mV − MV + 5)/5 . The hydrogen Balmer line H? has a wavelength of 486.1 nm. It is shifted to 559.7 nm in a quasar's spectrum. What is the redshift of this quasar? (Hint: What is Δ??)arrow_forwardHow astronomers determine the distance of a galaxy? Explain.arrow_forwardTry Now ... .... Listed below are some distances from Earth to other objects in the Milky Way galaxy. Convert each distance to light-years. (Each of these distances is less than one light-year. For an added challenge, convert each distance to light minutes or light seconds.) 1. The distance from Earth to the Moon is about 384,400 km. How many light-years is this? 2. The distance from Earth to Mars is about 784,000,000 km. How many light-years is this? 3. The distance from Earth to Pluto is about 5,750,000,000 km. How many light-years is this?arrow_forward
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