Physics PHYS 102
General Astronomy

Problem Set #5

 

After you finish this problem set, you should be familiar with:

granulation

spicules

prominences

limb darkening

corona

zeeman effect

chromosphere

sunspots

magnetic field

photosphere

sunspot cycle

Babcock’s dynamo

parallax

apparent magnitude

absolute magnitude

theoretical models of the Sun

p-p cycle

Spectral Type

conduction

solar neutrino problem

HR diagrams

convection

Magnitude

Temperature

radiative diffusion

Parallax

Color Index

E=mc2

Luminosity

 

Please answer the following questions using sentences and paragraphs.  When it is helpful, please use diagrams and equations.

  1. Explain how parallax is used to determine the distance to an astronomical object. If a star moved through an angle of 0.2 arc sec over a six-month period, how far away is it?  If its apparent magnitude is 7.0, what is its absolute magnitude?  If it is a main sequence star, what is its temperature?  What is its mass?
  2. In one comic-book episode from the early 1970’s, Superman, the "Man-of-Steel", flew right through the Sun.
    1. With the aid of a diagram, describe what Superman must have observed as he flew through the interior of the Sun. Please specify the temperatures and densities he found at various levels. Indicate regions where energy was transferred outward by convection and radiation. Show where he discovered nuclear reactions play an important role. Label the core, photosphere, chromosphere, and corona.
    2. If Superman were really made of steel, would he have been able to survive inside the Sun? Why or why not?

  1. Look at the surface of the Sun showing solar granulation in the movie below. Describe what you see, and offer an explanation.

     

  2. An image showing the magnetic field strength everywhere on the surface of the sun is called a magnetogram. Astronomers use magnetograms when they study sunspots.
    1. What is a sunspot. Make a drawing.
    2. Explain the sunspot cycle.
    3. Where are we in the sunspot cycle right now? When will the next minimum and maximum occur?
    4. Explain how a magnetogram is obtained. What is the Zeeman effect?
    5. From 1645 to 1715 virtually no sunspots were seen, and northern Europe experienced a "Little Ice Age" during which record low temperatures were recorded. What do you think -- could these two phenomena be related? Explain.
       
  3. Why didn’t the Sun "burn up" after only a few thousand years? List and explain the steps in the p-p cycle.
  4. This question deals with the so-called "solar neutrino problem".
    1. What is a neutrino? What makes neutrinos different than most other particles?
    2. How can neutrinos be detected here on Earth?
    3. What is the "Solar neutrino problem"?
    4. What is the currently accepted explanation of the "solar neutrino problem"?  Why?
       
  5. Check out the eclipsing binary star simulation at http://www.astro.cornell.edu/academics/courses/astro1101/java/eclipse/eclipse.htm. (NOTE: You may have to use Internet Explorer or Firefox and/or add the website as an exception for Java to allow the applet to run. Please test it earlier rather than later and let me know if you have problems!)  Using the simulation make a drawing of the light curve for
    1. two class M stars orbiting each other at a distance of 4 solar radii with the plane of the orbit inclined 2º to us.
    2. a class M  and a class F star orbiting each other at a distance of 4 solar radii with the plane of the orbit inclined 2º to us.
    3. a class M and a class A star orbiting at a distance of 4 solar radii with the plane of the orbit inclined 2º.
    4. explain the differences you see in the light curves.
  6. Estimate the mass of a main sequence star 10,000 times as luminous as the Sun. What is the luminosity of a main sequence star whose mass is 1/10 that of the Sun?  What is the surface temperature of a main sequence star the is 100 times as bright as the sun? 

 

Here are some practice "figure it out rather than memorize" type questions.  They will not be graded as part of the homework (so don't turn them in), but they may be useful as you prepare for the test.  More questions like these can be found in the test practice folder at the library.

1.

A star of apparent magnitude +3.5 appears

 

A)

fainter than a star of apparent magnitude +3.3.

 

B)

either brighter or fainter than a star of apparent magnitude +3.3, depending on the distance to the stars.

 

C)

brighter than a star of apparent magnitude +3.3.

 

D)

farther away than a star of apparent magnitude +3.3.

 

2.

A star is 80 pc from the Sun.  Its apparent motion against the background sky as a result of the Earth's motion through 1 AU, that is, its stellar parallax, is

 

A)

80 arcseconds.

 

B)

0.0125 arcsecond.

 

C)

0.0125 arcminute.

 

D)

0.0125 radian, or 0.72°.

  

3.

If a distant cluster were to be composed only of stars with apparent magnitude of +3, how many of these stars would there be in this cluster if its apparent magnitude matched that of a star with apparent magnitude of +1?

 

A)

102, or 100

 

B)

About 2.5

 

C)

Between 6 and 7

 

D)

2

  

4.

Suppose that two identical stars (having the same total light output) are located such that star A is at a distance of 5 pc and star B is at a distance of 25 pc. How will star B appear, compared to star A?

 

A)

Star B will be 1/20 as bright as star A.

 

B)

Star B will be 1/5 as bright as star A.

 

C)

Star B will be 1/25 as bright as star A.

 

D)

Star B will be 1/2.2 as bright as star A.

  

5.

The Sun has an absolute magnitude of +4.8.  How far away would we have to go in order for the Sun to be just barely visible to the naked eye (6th magnitude)?

 

A)

22.4 pc

 

B)

17.4 pc

 

C)

1.2 pc

 

D)

6 pc

  

6.

A star whose distance from the Earth is 100 pc has an apparent magnitude of m +2.5.  What is its absolute magnitude?

 

A)

+7.5

 

B)

–2.5

 

C)

–47.5

 

D)

–7.5

 

7.

Determine the spectral class of a star with the following absorption lines in its spectrum: “H lines moderately strong; He I lines present; no Ca II, Fe II, or He II lines.”

 

A)

F

 

B)

A

 

C)

B

 

D)

M

  

8.

Two stars have the same luminosity (or absolute magnitude). One star is spectral class F and the other is spectral class K. From this information, we know that

 

A)

the B-type star is hotter but can be larger, smaller, or the same size as the K-type star.

 

B)

the K-type star is larger than the B-type star.

 

C)

the K-type star is hotter but can be larger, smaller, or the same size as the B-type star.

 

D)

the B-type star is larger than the K-type star.

  

9.

Use the Hertzsprung-Russell diagram and the mass-luminosity relation to estimate the mass of Vega, which is an AO V main-sequence star with a surface temperature of about 10,000 K.

 

A)

Between 5.0 and 10.0 solar masses

 

B)

Between 1.5 and 5.0 solar masses

 

C)

About 10 solar masses

 

D)

less than 1.0 solar masse