Starry Night Homework Nats 102, Spring 2006
Due: Thursday, Jan. 26 Bechtold and Oppenheimer
Type your 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.
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"...)
Polaris is fainter than Sirius
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?
Polaris doesn’t move at all, it stays in the same position.
3. How would you describe the motion of other stars relative to Polaris?
Explain and draw a simple diagram to illustrate.
They all circle around Polaris. Draw circular paths of stars going around Polaris.
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?)
If you draw a line from the two stars at the end of the big dipper, they should connect with 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?
Polaris is always in the same position in the sky and indicates where north is. It can be used for
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 Crux points to the South Celestial Pole.
[The northern hemisphere is lucky to have Polaris, and the southern hemisphere is lucky to have the Southern
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?
There are a lot of correct answers for what is always up: The North Star, The Little Dipper (Ursa
Minor), Cepheus, Cassiopeia (The W), Camelopardalis, Draco, anything above about 60-degrees North
7. Change your location to the North Pole. Are any stars or constellations always above the horizon here?
Every star/consetellation in the northern hemisphere is above the horizon
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?
It is pretty far up in the sky in the SW or S direction.
2. Move date forward 2 months (late Mar.) Where's Orion?
Near the west, about to set.
3. Move date forward 1 month (late Apr.) Where's Orion?
Below the horizon/just set.
4. Move date forward 1 month (late May) Where's Orion?
Below the horizon.
5. Move date forward 2 months (late July) Where's Orion?
Still below the horizon.
6. Move date forward 3 months (late Oct.) Where's Orion?
Rising in the east.
7. Move date forward 1 month (late Nov.) Where's Orion?
In the E/SE, higher than 6.
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.
Orion rises at around 9-9:30 pm, travels from east-to-west, but doesn’t set before the sun rises.
9. Return the date to tonight, 9 pm. What constellation is rising in the East? (use Auto Idenitfy under
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 mintues [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
(If you want to learn the constellations, a fun book is H.A. Rey's "The Stars", which is in the Science Library.)
SO THE CONSTELLATIONS CHANGE POSITION WITH THE SEASONS. THIS (AND
EVERYTHING IN 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'
Saturn and Mars.
2. Advance the clock to March 27 at 10 pm. What planets are visible and where are they?
Saturn and Mars (again). Same as 1, but this time both are further west.
3. Advance the clock to June 16 at 10 pm. What planets are visible and where are they?
Jupiter (in the south) and Pluto. Mars is just setting.
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 "regrograde motion"; you can learn about it in the general astro textbook on
Mars should be moving west-to-east with respect to the stars at first, and then reverse direction (moving
east to west) for a little while, and then almost stop again and turn around and go west-to-east.
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?
Mars is experiencing retrograde motion, it appears to stop and turn around twice.
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 7 pm?
In the west, about to set.
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
It will be a morning star on April 19, 2006.
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).
This question was sort of a typo, I meant the last two times to be in 2006, so answers of Jan 19, 2005 or
Jan, 19 2006 work, same with April 19, 2005/2006. These are approximate time.
August 19 2005 (evening star) a. 6:45 pm b. 8:30 pm c. 1:45
December 19 2005 (evening star) a. 5:10 pm b. 7:35 pm c. 2:25
January 19 2005 (morning star) a. 7:30-7:45 am b. 6:35-6:50am c. about 1:00
April 19 2005 (evening star, barely) a. 6:40 pm b. 7:00 pm c. about 15-20 mins
January 19 2006 (morning star) a. 7:30-7:50 am b. 6:40-7:00 am c. about 50 mins.
April 19 2006 (morning star) a. 6:00 am b. 3:40 am c. 2:20
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.)
July-December 2005 (evening star)
January 2006 (morning star or can’t be seen)
July 2006 (morning star)
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
Near the western horizon, it is a waxing crescent.
2. Move the date forward 1 day. Do this 13 times. Describe how the moon's phase and distance from the sun
The moon gets fuller and moves farther away from the sun.
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?
The moon is about at first quarter. It is up at least half the night, but not the full night.
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]
The moon is in its last quarter (waning). It is up about half 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?
Waning crescent. At least half the day, but not the full day.