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The following examples demonstrate the powerful
capabilities of Starry Night. Going through them step by
step is a great way for you to become familiar with the
program. They would also make a good beginning to any
lecture on Astronomy, or the basis for a study period in
schools.
Examining Comet Orbits
Compared to the planets, comets have highly elliptical
orbits that carry them well out of the plane of the Solar
System. Using traditional media, it is often difficult for
students to fully grasp these orbital relationships. Starry
Night's three-dimensional renderings and time control
features make it easy to understand these complicated
orbits. This exercise examines the orbit of the comet
Hale-Bopp, and how it relates to the orbits of the inner
planets, including the Earth.
Example: Comet Hale-Bopp
- Open a new window.
- Using the Tool Palette, lift off from Earth, until
you're about 4 AU's away from the Earth. (AU =
Astronomical Units, 1 AU is equal to the average distance
from the Earth to the Sun)
- Using the Planet Palette, lock on the Sun. This will
keep the Sun centered in your view.
- Using the Planet Palette, click Go There. This will
move your location to the Sun (although still 4 AU's
above it.)
- From the Tool Palette, click Location. When the
Location Window opens, check the Hover box. Then click
Set Location to close the window. You are now hovering
over the Sun, at 4 AU's. (This will eliminate any effects
that the Sun's rotation would have on your view.)
- If the astronaut's feet are on, and you wish to turn
them off, choose "Feet" from the Guides Menu.
- Using the Planet Palette, turn on the orbits of
Mercury, Venus, Earth, Mars, Jupiter, Saturn, and Comet
Hale-Bopp. Comet Hale-Bopp's is the purple orbit.
- From the Settings menu, choose Orientation/ Ecliptic.
This will align your view to that of the ecliptic, the
plane in which most of the planets orbit around the
Sun.
- Using the Location Scroller Tool, you can adjust your
view so that you're looking along the ecliptic plane,
similar to the example file "Hale-Bopp orbital
plane".
- Using the Time Palette, set the Time Step to 3 days.
Then press the Time Forward button (it looks like the
"Play" button on a VCR). As time advances, you will see
the planets orbiting in the ecliptic plane, and Comet
Hale-Bopp coming in from the outer solar system and
sweeping around the Sun.
- If you wish, you can turn on the planets' names by
selecting Options from the Settings menu. When the
Options Window opens, use the menu to select Planets.
Then click on the Options tab, and check the Labels box,
making sure that the Show Names button is selected.
By running time backwards and forwards, and using the
Location Scroller to
adjust your view, you can get a sense of the relationships
between the orbit of the comet and the orbits of the
planets. Starry Night makes these concepts easier to
understand, and at the same time, its ease of use and "fun
factor" encourages further exploration and learning.
This exercise has a matching example file that can be
found on the CD, in the Example File folder, in the
Exercises subfolder. Double click on the file to open it, or
drag and drop it into any open Starry Night window and it
will open automatically.
Examining Orbital Elements
Celestial mechanics is usually passed over in
introductory Astronomy courses, because the mathematics and
time needed to grasp orbital concepts is just too involved
for most students.
Starry Night changes all this. By providing an
interactive simulator where the orbital elements of an
object can be changed in a visual manner, an incredibly
complex subject can be made not only understandable, but
fun.
Example: Creating a New Asteroid
In this scenario we will put an asteroid into orbit
around the Sun, and observe how the orbital elements affect
the orbit. The goal is to gain insight into the meaning of
each of the orbital elements.
- Open the Planet Palette and select the Sun by
clicking on it once.
- Now bring up the Orbit Editor window by clicking on
the 'Add' button.
- By default, the name of the new object will be
"Untitled".
- Notice the tabs across the top of the editing area,
select the first tab, called 'Info' and give the asteroid
a new name.
- Select the "Type of Object" to be an Asteroid.
- Now select the Orbital Elements tab.
You can use the sliders to interactively change each of
the orbital elements. For instance, try moving the
inclination slider. You'll get firsthand knowledge of the
meaning of "inclination" -- a tilt in the orbit -- and the
slider provides almost instantaneous feedback to any changes
you make.
Try the other sliders:
Ascending Node: moves the node markers around
(the little triangles).
Arg of Pericenter: moves the pericenter marker around
(the little line). The pericenter marks the spot where
the new planet comes closest to the parent body around
which it orbits.
Mean Distance: the size of the orbit.
Eccentricity: the higher the number, the more
elliptical the orbit gets.
Mean Anomaly: the position of the planet in the
orbit.
Now select the Axis/Rotation/Size tab. Use the Pole
Position and Diameter sliders to further customize your new
asteroid.
If you like, you can paste in planet maps using the
Surface tab.
Press Save. The planet you have created is now a first
class citizen of Starry Night. You can now take a trip there
and view the Earth from the new Asteroid. To do that, go to
the planet floating palette again, and select your new
asteroid.
Click on the 'Go There' button.
Do a "Find" for Earth, or simply double-click the Earth's
name in the Planet palette. You are looking at Earth from
the vantage point of the new asteroid.
To eliminate the planet you have created, select it, then
hit the delete button.
The Ecliptic Plane
When we look at the sky we see stars in every direction,
but planets are always found within a relatively narrow band
of sky that defines the constellations of the zodiac. The
planets and the Sun wander about this limited region of sky
but never leave it. Why? The answer lies in the relative
positions of our viewing platform (the Earth) and its fellow
planets in the solar system. Instead of being strewn about
the Sun in random positions, all of the planets' orbits are
confined to a fairly flat disc. The projection of this disc
onto our sky is the zodiacal band.
STEP 1: Illustrating that the planets are confined
to a narrow strip of sky.
Open the Planet Palette. This demonstration may be done
with daylight on or off. Planet by planet, turn on the
orbits. Note: It is best to start at Mars and continue to
Neptune. Pluto is a special case since it is aligned
slightly out of the orbital plane of the rest of the
planets.
Now turn on the orbits of Mercury and Venus. Mercury and
Venus are interesting because the whole circle of their
orbits may be seen on the screen since they circle the Sun
within the Earth's orbit.
STEP 2: Show that the planets are found in the
constellations of the zodiac.
Go to the Settings menu and select
Options>Constellations. In the General tab folder, check
the "Show Constellations", as well as the "Zodiac only"
checkboxes. You may also turn on the constellation
boundaries, found in the Boundaries tab. Click OK. You will
now be seeing the orbits of the planets passing through the
zodiacal constellations. (In fact, this is what defines the
zodiacal constellations.)
STEP 3: Show the same thing from a wider
perspective.
Go to the Settings menu and select Options>Planets. In
the General tab folder, make sure that the "Show Planets"
and "Labels" checkboxes are checked, and that the Show names
radio button is pressed. With the constellations of the
zodiac turned on, in addition to the orbits of the planets
Mercury through Neptune, use the Planet Palette to center on
the Earth (use the Lock icon) and do a "lift-off" using the
Elevation Up button. Lift off to a point about 10 to 20 AU
away from Earth.
The disc-like nature of the orbits can be seen if you use
the Location Scroller on the main Tool Palette. As you
scroll, you can clearly see the plane of the orbits, and
their relationships to each other.
STEP 4: Introducing the Ecliptic Plane
Go to the Settings menu and select Options>Ecliptic
Guides. Check the Show "Ecliptic Guides" and "Reference
Plane" checkboxes. Now you can use the location scroller to
see that the green mesh of the ecliptic plane is the plane
of the Earth's orbit and all show how close the other orbits
are to it.
One fun thing to do is to get yourself into the plane of
the ecliptic, lift off further (to say 150 AU) and turn on
the orbit of Pluto. This illustrates how far off of the
ecliptic plane Pluto is.
Try turning on a few of the comet orbits such as
(Halley's or Hyakutake's) to see how unusual their orbits
are.
This exercise has a matching example file that can be
found on the CD, in the Example File folder, in the
Exercises subfolder. Double click on the file to open it, or
drag and drop it into any open Starry Night window and it
will open automatically.
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