Astronomy
1st Edition
ISBN: 9781938168284
Author: Andrew Fraknoi; David Morrison; Sidney C. Wolff
Publisher: OpenStax
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Textbook Question
Chapter 17, Problem 39E
Star A and Star B have different apparent brightnesses but identical luminosities. If Star A is 20 light-years away from Earth and Star B is 40 light-years away from Earth, which star appears brighter and by what factor?
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Students have asked these similar questions
Star A has an apparent magnitude of –1.5 and is 12.6 light-years from Earth. Star B has an apparent magnitude of 0.4 and is 15.6 light-years from Earth.
Why should apparent magnitude NOT be used to determine which star is brighter? What information could help you determine which star is brighter?
Distance from
Apparent Brightness (rank;
brightest, 8 = dimmest)
Name of Star
Earth (light years) | 1 =
Sun
Sirius
8.6
Canopus
Arcturus
309
3.
36.7
4
Rigel
Vega
Alpha Centauri
Bernard's Star
773
5
25.3
4.3
7
5.9
8
13 What sentence explains why a star can be much farther from Earth than
the Sun, but still be bright?
nida nenv
A. Distance from Earth and apparent brightness are related.
B. Bright stars that are farther away are larger than the Sun.
C. The higher it appears in the sky, the brighter the star.
D. The apparent brightness scale goes up as stars get dimmer.
del sdT
In the parallax method of determining stellar distances, the angle to a star is measured while
the earth is on one side of the sun and then again six months later, as in the diagram below.
Assume the earth-sun distance is 1 Astronomical Unit. The parallax angle of Alpha Centauri
is 0= 2.1 x 10-4 ° . Find the distance from the sun to a Centauri in light years. Assume a
circular orbit for the Earth.
a Centauri
Earth (June)
Earth (December)
Sun
Chapter 17 Solutions
Astronomy
Ch. 17 - What two factors determine how bright a star...Ch. 17 - Explain why color is a measure of a star’s...Ch. 17 - What is the main reason that the spectra of all...Ch. 17 - What elements are stars mostly made of? How do we...Ch. 17 - What did Annie Cannon contribute to the...Ch. 17 - Name five characteristics of a star that can be...Ch. 17 - How do objects of spectral types L, T, and Y...Ch. 17 - Do stars that look brighter in the sky have larger...Ch. 17 - The star Antares has an apparent magnitude of 1.0,...Ch. 17 - Based on their colors, which of the following...
Ch. 17 - Order the seven basic spectral types from hottest...Ch. 17 - What is the defining difference between a brown...Ch. 17 - If the star Sirius emits 23 times more energy than...Ch. 17 - How would two stars of equal luminosity-one blue...Ch. 17 - Table 17.2 lists the temperature ranges that...Ch. 17 - Suppose you are given the task of measuring the...Ch. 17 - Star X has lines of ionized helium in its...Ch. 17 - The spectrum of the Sun has hundreds of strong...Ch. 17 - What are the approximate spectral classes of stars...Ch. 17 - Look at the chemical elements in Appendix K. Can...Ch. 17 - Appendix I lists some of the nearest stars. Are...Ch. 17 - Appendix J lists the stars that appear brightest...Ch. 17 - What star appears the brightest in the sky (other...Ch. 17 - Suppose hominids one million years ago had left...Ch. 17 - Why can only a lower limit to the rate of stellar...Ch. 17 - Why do you think astronomers have suggested three...Ch. 17 - Sam, a college student, just bought a new car....Ch. 17 - Would a red star have a smaller or larger...Ch. 17 - Two stars have proper motions of one arcsecond per...Ch. 17 - Suppose there are three stars in space, each...Ch. 17 - What would you say to a friend who made this...Ch. 17 - In Appendix J, how much more luminous is the most...Ch. 17 - Verify that if two stars have a difference of five...Ch. 17 - As seen from Earth, the Sun has an apparent...Ch. 17 - An astronomer is investigating a faint star that...Ch. 17 - The center of a faint but active galaxy has...Ch. 17 - You have enough information from this chapter to...Ch. 17 - Do the previous problem again, this time using the...Ch. 17 - Star A and Star B have different apparent...Ch. 17 - Star A and Star B have different apparent...Ch. 17 - The star Sirius A has an apparent magnitude of 1.5...Ch. 17 - Our Sun, a type G star, has a surface temperature...
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- As seen from Earth, the Sun has an apparent magnitude of about 26.7 . What is the apparent magnitude of the Sun as seen from Saturn, about 10 AU away? (Remember that one AU is the distance from Earth to the Sun and that the brightness decreases as the inverse square of the distance.) Would the Sun still be the brightest star in the sky?arrow_forwardIs the Sun an average star? Why or why not?arrow_forwardStar A and Star B have different apparent brightnesses but identical luminosities. Star A is 10 light-years away from Earth and appears 36 times brighter than Star B. How far away is Star B?arrow_forward
- The star Sirius A has an apparent magnitude of 1.5 . Sirius A has a dim companion, Sirius B, which is 10,000 times less bright than Sirius A. What is the apparent magnitude of Sirius B? Can Sirius B be seen with the naked eye?arrow_forwardDescribe two ways of determining the diameter of a star.arrow_forwardConsider two identical stars, A and B. Star B is 10 times farther away than star A. What is the differencein magnitudes between the two stars?arrow_forward
- Stars A and B both have the same spectral class. Star A is 7 times farther away than star B. The brightness of star A will be ________ times dimmer than B. (Give a number.)arrow_forwardUse a diagram to explain what is meant by the parallax angle, p, for a star observed twice from Earth, with a 6-month interval between each observation. Hence define the parsec, and calculate its value in astronomical units and metres. The star Betelgeuse is observed to have a parallax angle p = 4.5 × 10−3 arcseconds. State the distance of Betelgeuse in units of parsecs and light years.arrow_forwardYou measure a star to have a parallax angle of 0.12 arc-seconds. What fraction of a degree is this? By how many times would you have to magnify this effect for it to be visible to the human eye? (The limit of human vision is about 1 arc-minute) What is the distance to this star in parsecs? What is the distance to this star in light years What is the parallax angle of a different star that is twice as far away as the star from the previous problems? [answer in arc-seconds without including the unit]arrow_forward
- A nearby star, Proxima Centauri , has a parallax of 0.772 arcseconds. How long does it take the light from this star to reach us?arrow_forward15: A star has a parallax angle of 0.0270 arcseconds and an apparent magnitude of 4.641. What is the distance to this star? Answer: 37 16: What is the absolute magnitude of this star? Answer:1.8 17: Is this star more or less luminous than the Sun? Answer "M" for More luminous or "L" for Less luminous. (HINT: the absolute magnitude of the Sun is 4.8) Answer: M 18: What is the luminosity of this star? (HINT: The luminosity of the Sun is 3.85×1026 W.) Please answer question #18, #15-17 are correct, the photos provide the work for them.arrow_forwardYou measure a star to have a parallax angle of 0.12 arc-seconds What is the distance to this star in parsecs? 8.33 Hint: d = 1/p What is the parallax angle of a different star that is twice as far away as the star from the previous problems? [answer in arc-seconds without including the unit]arrow_forward
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