Starry Night Lab
Nats 102, Spring 2006
Bechtold & Oppenheimer
Due: Tuesday, Feb. 7, 2006
TYPEyour answers. Diagrams and the table for Part V can be neatly hand-written.
[Lisa points out that the North Star is useful for navigation]
Homer: That's nice, Lisa, but we're not in astronomy class. We're lost in the woods.
-The Simpsons
Part I. Polaris, and how nearby stars move over a night.
0. Set Location = Tucson, and Time = tonight @ 8 pm. Use Find (Ctrl-F) to find Polaris (also called the North Star). Not coincidentally, you'll find it above the northern horizon.
1. Brighter stars look bigger in Starry Night. Find the star named Sirius, note how big it's shown, then go back to Polaris. Roughly how bright is Polaris compared to Sirius? ("brighter", "fainter", "same"...)
2. Run time forward (3000x works best) over 1 night and watch Polaris. (If you Find an object, Starry Night will keep it centered as time passes.) How would you describe Polaris' motion in the sky?
3. How would you describe the motion of other stars relative to Polaris?
Explain and draw a simple diagram to illustrate.
4. Turn on Constellations (Labels and/or Stick Figures). Find Ursa Major, then find the Big Dipper within.
Center on Polaris, run time forward over 1 night, & watch the Big Dipper. (Note: You may need to zoom out to see this. How can the Big Dipper help you find Polaris? Explain in 1 sentence and draw a simple diagram to illustrate. (Hint:Are there any sets of stars that always face Polaris?)
[You might ask, "Why not just use the Little Dipper, since Polaris is actually in it? The answer is, the Big Dipper is much brighter than the Little, so it's easier to find.]
5. Based on what you've learned in this exercise, why do you think Polaris is important?
6. Change your LOCATION to anywhere in the southern hemisphere. Look South
and run time over 1 night. Is there a bright South Star that doesn't move?
7. How can you locate the South Celestial Pole using the constellation The Southern Cross (aka Crux)?
[The northern hemisphere is lucky to have Polaris, and the southern hemisphere is lucky to have the Southern Cross.]
Part II. How the stars move during a night.
0. Set location = Tucson (click 'Home' under location). Set time to tonight at 8 pm. Set the Time Flow Rate to 3000x and run Starry Night for 24 hours. Do this a few times, looking at the East horizon, then West, then South using the appropriate icons on the toolbar. [You've already done North in Part I.]
1. In what cardinal direction do stars rise above the horizon?
[Cardinal = North, South, East, or West]
2. In what cardinal direction do stars set [move below the horizon]?
3. In what direction does the sun rise? In what direction does it set?
4. [There's no write-up for this question, but you'll need the experience to answer #5.]
Grab any ball (basketball, tennis, whatever) for this section. This is your Earth. Make a small pen dot to indicate the north pole (or use the inflation hole.) Place another dot roughly halfway between the North Pole and the Equator -- that's you. Pick a distant object to represent a star. Slowly turn your Earth, watching the "you" dot. At some point in the rotation, your "Star" won't be visible to you-dot. Then it should rise, be visible to you-dot, and then set (not be visible to you-dot.)
THE STARS APPEAR TO MOVE THROUGHOUT THE NIGHT BECAUSE THE EARTH IS TURNING. THE SUN RISES AND SETS FOR THE SAME REASON.
5. Use your Earth-ball and your answers to questions II-1 and II-2 to answer this:
Which way does the earth turn, clockwise, or counterclockwise? (From the perspective of someone standing over the North Pole.)
6. Are any stars or constellations always above the horizon from Tucson? Which ones?
7. Change your location to the North Pole. Are any stars or constellations always above the horizon here?
Which ones?
Part III. How the sky changes over the year.
Now we'll explore how our view of the sky changes with the seasons.
1. Set time for tonight around 10 pm. Use Find to find the constellation Orion. What direction and approximately how high in the sky is it?
2. Move date forward 2 months (late Mar.) Where's Orion?
3. Move date forward 1 month (late Apr.) Where's Orion?
4. Move date forward 1 month (late May) Where's Orion?
5. Move date forward 2 months (late July) Where's Orion?
6. Move date forward 3 months (late Oct.) Where's Orion?
7. Move date forward 1 month (late Nov.) Where's Orion?
8. Set the date for November 1, 2006, 7 pm. Find Orion. Run time forward over one night and follow Orion. Describe Orion's motion over the course of the night.
9. Return the date to tonight, 9 pm. What constellation is rising in the East? (Use Auto Identify under Constellations)
10. Set for 9 pm, 10 days in the future. Where is the constellation you found before (higher or lower)? Go to 9 pm, 20 days from now and see where the constellation is now.
11. Summarize what you've just found: (circle the right answer)
A given star rises 4 minutes [earlier/later] each night.
We call Orion a winter constellation because it's prominent in the after-dark winter sky, but you can find it in the summer -- just look in the early morning. It keeps rising 4 minutes earlier every day, until by fall, it's visible before midnight. (If you want to learn the constellations, a fun book is H.A. Rey's "The Stars", which is in the Science Library.)
SO, THECONSTELLATIONS CHANGE POSITION WITH THE SEASONS. THIS, (ANDEVERYTHINGIN PART III) HAPPENS BECAUSE THE EARTH IS GOING AROUND THE SUN.
How does that work? Well, night is when our part of Earth faces away from the sun; as the Earth revolves around the sun, the direction opposite the sun (midnight) points to different stars. To illustrate this, grab your Earth-ball, call something nearby the Sun (like your roommate's head), and move the Earth in a circle around the Sun. As you move, notice what's in the opposite direction of the Sun (from the Earth's perspective). Note that different stuff appears opposite the sun as the Earth orbits. So what constellation is overhead at a given time changes in a 1-year cycle.
Part IV. The Planets.
0. Turn on Guides/Ecliptic. The word "ecliptic" means the plane of the solar system. The planets (including Earth), the sun, and the moon all lie roughly in this plane. From Earth, we see the ecliptic as an arcing line across the sky, along which the sun, moon, and planets travel.
1. Set the clock for tonight at 10 pm. What planets are visible, and where are they? [The "Find" option may help or click the 'Labels' checkmark next to the 'Planet-Moon' item under the 'Solar System' in the 'Options' tab.]
2. Advance the clock to March 27 at 10 pm. What planets are visible and where are they?
3. Advance the clock to June 16 at 10 pm. What planets are visible and where are they?
4. Use“Find” to find the planet Mars (so Starry Night will follow it). Set date = 8/1/2005, time=midnight, and Time Flow Rate= 1 day. Run Starry Night forward in time to year's end, and watch Mars carefully. (You'll probably need to run it several times.) Watch how Mars moves with respect to the stars as time passes, and describe it carefully. [This is called "retrograde motion"; you can learn about it in the textbook, or the interactive figures on the class web site.]
5. Set date = 10/1/2005, time=midnight, and timestep= 1 day. Click the "| > " button to advance a day at a time until mid-December. Does Mars change position with respect to the stars from night to night?
Part V. Venus.
In this section we're going to see where the planet Venus will be in the sky over the next 12 months. Venus is the brightest object in the sky except for the Sun or Moon. (The visible light we see from Venus is actually sunlight reflected off Venus's thick clouds.)
Because Venus is so bright, and because it moves quickly in the sky, it's been important to human mythology.
1. Where was Venus on July 19, 2005 at 7 pm?
2. When Venus is East of the Sun (East is LEFT on your screen) it's visible in the evening sky. Since objects move east to west because of the spin of the Earth (which is west to east), an object east of the Sun sets AFTER the Sun. In this case it would be called "an evening star". The opposite is true if Venus is west of the Sun, it would be visible just before dawn and would be "a morning star."
So, quickly move from July 19, 2005 to April 19, 2006. Will Venus be an evening star or a morning star at the end?
3. We'd like you to find out some Venus information for the following dates: Aug. 19 2005, Dec. 19 2005, Jan. 19 2005, April 19 2005.
If Venus is east of the Sun, so it's setting later than the Sun, please tell us three things:
a) time of Sunset; b) time of Venus-set; c) how long Venus is up after sunset (subtract a from b).
[Use 3000x speed to advance backwards or forwards to see setting times]
If Venus is west of the Sun, so it's rising earlier, give us:
a) time of Sunrise; b) time of Venus-rise; c) how long Venus is up before sunrise (subtraction again).
Venus is so bright that if it's in the sky more than 1/2 hour after sunset or earlier than 1/2 hour before sunrise, it's very easy to see.
4) From July. 19, 2005 to July 19, 2006, in monthly intervals, tell me if Venus is a morning star, an evening star, or can't be seen. We'll define "can't be seen" as rising or setting within a half hour of the Sun. So you'll need a little table here. (hand-drawn is okay if neat.)
Part VI. The Moon.
1. Do Find "moon". Set date = 2/1/2006 and time= 7 pm. Where is the moon? What phase is it (or how full is it?)
2. Move the date forward 1 day. Do this 13 times. Describe how the moon's phase and distance from the sun changes.
3. Set date = 1/7/2006, time=7 pm. What phase is the moon? Run the simulation until sunrise. Describe the moon's motion. What fraction of the night is it up?
4. Set date = 12/22/2005, time=7 pm. Run from 7 pm to 7:30 am, and describe the moon's phase and its motion. What fraction of the night is it up? [Note: it shouldn't be up yet, but it should rise in the night]
5. Set date= 12/25/2005, time =7 am. What phase is the moon? Run simulation until 7 pm. What fraction of the DAY is the moon up?