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The Stars 1

This sheet of questions goes with the packet handed out in class including information from Star-Finding with a Planisphere by Alan M. MacRobert and The Edmund Sky Guide by Terence Dickinson and Sam Brown.

Reading Questions

Answer the following questions based on the handout and your planisphere. Use complete sentences in your answers: some answers will require frequent returns to the text to figure out and you will need to use more than one sentence in some cases.

A few ideas for class presentations for this material. Do these after students have wrestled with answering the questions using their planispheres and imaginations.

Use SkyViewCafé to simulate the motion of the sky showing circumpolar constellations, rising in the East and setting in the West. Also show stars in the South seeming to move from left to right.

Use SkyViewCafé and the overhead projector to show how the height (altitude) of Polaris changes with latitude. You can just use the arrows on the keyboard to change the latitude north and south. Also, change longitude at constant latitude to show that a planisphere good at 45° N is good anywhere on that latitude.

Use SkyViewCafé to show stars at the zenith at 22:00 on 3/21, 6/21, 9/21, and 12/21.

Stars farther away look dimmer due to the Inverse Square Law./

  1. Use your planisphere to simulate the motion of the sky from dusk to dawn (17:00 to 07:15 during Jan or 17:00 to 05:30 in Sept). Make sure that stars rise in the E and set in the W. Do you see any constellations which never rise or set all night? Keep turning the planisphere as if you could see all the stars during daylight hours. Do any of those stars you noticed earlier rise and set? Constellations (and stars) which never rise or set are called circumpolar because they circulate around the pole. What are the circumpolar constellations on your planisphere?
  2. The altitude (height in degrees from the horizon) of the North Celestial Pole equals the latitude of the observer. So if you need to know your latitude you need only measure the altitude of Polaris. Knowing this, answer the following questions:
    1. Are there more or fewer circumpolar constellations if you are in Alaska, say at a latitude of 71°N? This is 28° farther north than where we are here in Maine. What constellations would be circumpolar at this high latitude? What constellations would never rise above the horizon? (Use your planisphere to make educated guesses).
    2. Are there more or fewer circumpolar constellations if you are in El Salvador, say at a latitude of 13°N? This is 30° farther south than where we are here in Maine. What constellations would be circumpolar at this low latitude? Do you think that there might be stars visible from this latitude that we can’t see from where we are? Why or why not? (Use your planisphere to make educated guesses).
  3. The stars you can see in different seasons are different. Look at the stars near the zenith at 10 pm on Mar 21, Jun 21, Sep 21, and Dec 21. What causes the change in the overhead stars as you move through the year? Draw a picture showing the Sun, the Earth and background stars to help make this explanation.

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  1. The Earth rotates from W to E (look at this rotation using a globe). Why do the Sun, Moon, planets and stars rise in the E and move toward the W?
  2. The distances between the stars are unimaginably immense and are measured in light-years. A light-year is a unit of distance. Define this distance in your own words.
  1. Look at the list of the 50 brightest stars. They vary from 8.7 light-years to 2,100 light-years away. Focus your attention on the five stars listed at right. Using the chart calculate the distance to each of these stars in miles. There are 5.9 × 1012 miles in a light-year (5,900,000,000,000 mi).
  2. How long would it take to travel to each of these stars at the following speeds?
    Space Shuttle in orbit: 1.7 × 104 (17,000) mi/hr
    Voyager 2: 3.6 × 104 (36,000) mi/hr
    Speed of Light: 6.7 × 108 (670,000,000) mi/hr
    Hint: Multiply by 8,760 hr/yr to convert speeds to miles per year. Speed equals distance divided by time: s = d/t. So time equals distance divided by speed: t = d/s.

  3. How old is the light that reaches us from each of those stars?
  4. How is looking at the stars a bit like traveling through time?
  5. How is it possible for Canopus to be so much farther away than Sirius but still be nearly as bright?
  6. Why is Saiph near the bottom of the list of the 50 brightest stars when it is 50,000 times brighter than the Sun?

Define the following terms in your own words.

  1. circumpolar:
  2. altitude:
  3. magnitude:
  4. luminosity:
  1. Milky Way Galaxy:
  2. light-year:
  3. dwarf star:
  4. giant star:
Last updated: Sep 09, 2009        Home