This supplement is meant to aid TA's and instructors. It assumes that the homework data is being collected with Voyager, though that is not essential for this to be useful. It also introduces students to Voyager and uses the Mac's large display screen to help explain some concepts that the students can follow up on their own time using classroom Macs. It is intended that the TA's should run through this once as practice before trying to teach it.

As with the assignment text, this lab needs to be updated each time it is used to accurately reflect what's in the sky.

Pre-assignment demonstration

Before class, do the following:

• Start up Voyager.

• Set the magnitude limits such that only stars brighter than 2nd magnitude appear.

• Set the local time to be 6 pm PDT on June 19, 1993 (be sure to type the whole year rather than just ``93''.

• Set View From Location to be Seattle, WA.

• Center and lock on the Moon.

• Set the timestep to 6 hours.

• Be sure you're zoomed out all the way.

During class, do the following exercises. All of them are optional. Simply choose what you think is best.

• Introduce some of the things about Voyager, maybe showing what the different coordinate systems look like (especially Local Horizon). For the demo, it is easier to stick with Star Atlas coordinates.

• Mention that the image of the Moon is only a representation of what it would actually look like in the sky...similarly for planets.

• Also mention that just because stars appear in the sky at some point, that doesn't mean you can see them. For example, in the startup screen after you've set up the demo, you'll see a bunch of stars around the Sun. That's what the sky would look like if the Sun weren't there.

• Call up the Ecliptic Coordinate Line, and explain to the class what it is. Keep this up throughout the demo and point out how the planets and the Moon all seem to remain near it.

• Disable locking and run time forward in steps of 2 minutes looking West in Local Horizon mode so that they can see how the sky looks at sunset. Afterwards, reenable locking and return to the starting time and Star Atlas coordinate system.

• Run the time steps forward (maybe in one or two hour time steps if you find it is going to quickly for six hour steps) and show how the Moon moves.

• Stop at certain points along the way to show when the Moon gets to the interesting points described in the assignment and verify everything, including the data in the table. If there is time, show what it looks like using the Local Horizon coordinate system.

• Verify angular separations by clicking on the Moon, double clicking on the Sun icon (in the planets bar...this centers on the Sun automatically rather than forcing you to find it), then clicking on the Sun, then typing Cmd-A. All the other information in the table can be gotten from the data cards that appear when you click the objects.

Post-assignment demonstration

Set up Voyager the same way you did before. Remind everyone what they are looking at, especially with the Ecliptic line. Do the following:

• Hide stars. They just get in the way for this demonstration.

• Change the view with ``Observe From Point...'' Go to Heliocentric Latitude of 90 degrees and a distance of 2.5 AU from the Sun.

• Double click on the Sun on the planets bar to center on the Sun. You should see the symbols for the inner four planets on the screen.

• Enable the trails option, lock to the Sun, and set the time step to be two days. Set it into motion. This is so that students can see planetary motion from a ``God's Eye'' perspective. The idea here is to get the students oriented in space, so they'll know where they are and what they are seeing.

• Change the Moon to a disk image, increase the magnification levels to their respective maximums (1000x for disk magnification, 100x for the Earth-Moon distance magnification). Note how incredibly oversized the Moon is in this image, and then let it go forward. The trails will display the Moon's path...note to the students how it is orbiting the Earth and always has the side facing the Sun lit.

• Stop at some point in the simulation and ask the students what they think the phase of the Moon is just from looking at the image from their perspective. Use ``Return to Earth'' to check by double clicking on the Moon icon and clicking on the Moon to check its data card. Do this a couple of times at different phases (like first vs third quarter) until most of them have it down.

• Use this demo to refute the ``Harvard Hypothesis''

• Observe from 90 degrees heliocentric latitude and 10 AU away from the Sun. Center on the Earth. Change the Moon disk magnification to 100x, and the Earth-Moon distance magnification to 100x. Zoom in all the way and then out one step...this should be a perfect scale. Now turn on the trails option and set the time step to 12 hours. Lock on the Earth and let it go forward. This should draw out the orbit of the Moon. We're supposed to see here that it looks elliptical, but it looks quite circular on first inspection. A closer look, though, will reveal the slight ellipticity, and students will pick this up. Ask them to guess where the Moon's angular size will be the smallest, then ``Return to Earth'' to check.

• Observe from a point that is 90 degrees in heliocentric longitude away from where you are and 1.5 AU away from the Sun (don't change the heliocentric latitude). Center and lock on the Earth. Make the Moon's image a disk with 100x magnification (so it's easy to see where the Moon is, but the Moon doesn't overpower the image). Turn off the inner planets except for the Earth and Moon. Now run it forward in time steps of 12 hours. NOTE: The ecliptic line now represent the orbital plane of the Earth. Explain this to them, noting that you are now looking at the Earth as if you were on Mars, observing it in ``quadrature''. A top view diagram on the board might help. What you should see after a little bit is that the orbit of the Moon is tilted slightly out of the plane of the ecliptic. Be sure everyone understands what they are looking at. Use this to answer the question on why eclipses don't happen every two weeks.

• Go out to a distance of 50 AU, lock on the Sun, enable trails, set the time step to 4 years, erase the line of the ecliptic, and let it go forward. This should show the definition of the plane of the solar system. You can then describe how the Moon's orbit is close to this plane, and so how, from our perspective, everything in the sky, including the Moon, always lies close to this plane in the sky. Be patient while explaining this one...it is difficult!

• If you have time, get into a discussion of correlation vs causation on the issue of the Moon's angular size and phase. Be creative on this one, and the discussion can be very helpful. It gives students a good idea with a very simple example of how science is done.