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Advantages:• Students learn about how to apply deductive reasoning• Students (hopefully) arrive at the correct conclusion on their own• It is a good way to “break the ice”Disadvantages:• Can take a long time• Can be frustrating to implement with unresponsive students2.2 Constellations and the ZodiacWe have found that some students can examine a good diagram froma textbook and immediately understand what is being depicted. Otherstudents have more trouble imagining what the two dimensionaldrawing is explaining about the three dimensional universe. In thefollowing activity, we attempt to explain the Sun’s apparent yearlymotion through the constellations of the Zodiac by making thestudents a part of the demonstration.We start by rearranging the classroom chairs to form a circle,with one chair placed at the centre where the tutorial leader sits.Pictures of the constellations are attached to the walls of the room,including the floor and ceiling, with the Zodiac constellations placedat eye-level.The students are told that the tutorial leader is the Sun, whileeach person seated represents the Earth at some point in its orbit.To make the point even clearer, the tutorial leader can hold a largeyellow ball, while the students pass around a smaller blue ball.The tutorial leader then asks the students to pass the Eartharound the circle and as each student gets the ball, they tell everyonewhich constellation the Sun appears to be in. If the constellations arein the correct order, then one can assign dates to each position alongthe Earth’s orbit. By having the students turn around to face the wall(and hence away from the “Sun”), they can see which constellationsare visible during the evening.Advantages:• Students get to think in three dimensions• Students get to participate• Students see the value of a model in understanding difficultconceptsDisadvantages:• Difficult to do with large numbers of students (> 30)2.3 Stellar ParallaxThe setup is identical to the previous one except now a “foregroundstar” is placed between the circle of chairs and the wall of constellations(the “background stars”). The students should now be comfortablewith the Earth going around the circle of chairs with the Sun in themiddle. However, now their attention will be focussed on the star.Each student in the circle tells the tutorial leader where theforeground star appears to be with respect to the background stars.The tutorial leader notes these positions and the students will be ableto ascertain the periodic movement of the apparent position of theforeground star. The students can also attempt to measure theparallactic angle and use trigonometry to calculate the distance tothe star.The advantages and disadvantages are similar to that experiencedfor the “Constellations of the Zodiac” tutorial.2.4 Sidereal vs. Solar TimeWe have found that this concept is one of the most difficult ones toteach in astronomy. Even the best diagrams lack motion and thereforethe notion of “time.” Scarborough College is equipped with a smallplanetarium (which can fit about 15 people), which we find is anexcellent resource for demonstrating difficult concepts, includingsidereal time. We also use celestial spheres (clear plastic spheres onwhich the constellations are inscribed and which have the earth atthe center of the sphere) to demonstrate the same things. In this way,the students can see what is happening from two different perspectives.We begin with the usual introduction to the night sky, includingthe constellations of the Zodiac. We then define, and demonstrate,a solar day and a sidereal day. Our planetarium is equipped with alarge “Sun” and a meridian, so it is very simple to demonstrate a solarday: the time between meridian crossings of the Sun. We thendemonstrate the sidereal day as the time between meridian crossingsof the stars. The students are then asked whether these times are thesame. The students are quick to realize that during the time betweensuccessive meridian crossings, the sun has moved a little along theecliptic, whereas the stars are still in the same location. The wholeexercise is repeated using the celestial spheres (which also have ameridian and moveable Sun).Advantages:• Students see phenomena in “real time”• Requires student participation to work well• Good practice for the teaching assistant’s “showmanship”Disadvantages:• For some students, seeing things from both perspectives can bemore confusing than enlightening• Requires technical expertise2.5 Telescope SimulationWith class sizes of about 150, it is not practical to have students visitan observatory and actually use a telescope to collect data. Fortunately,with the advent of networked computers, a lot can be done in acomputer lab to simulate how a real telescope works. Students canalso acquire real data from the Internet, which they can use to doprojects like main-sequence fitting of clusters. For many students,this type of activity gives them the feeling of doing “real” astronomyand an appreciation of the many uncertainties involved in acquiringdata through instruments.Until recently, we used the “TS24” telescope simulator to havestudents perform main sequence fitting of an open cluster. Thesimulator was very sophisticated, and one could easily incorporateDecember / décembre 2000 253JRASC