Teachers' Guide

Activity 2.1--Part 2

Mars: Off the Charts-- until YOU put it there! Engage With appropriate warnings about night-time precautions, and an invitation to work with parents or other caregivers, invite students to observe the night sky (viewed toward the East) as a homework assignment. (Brainstorm and suggest strategies for determining East from their homes.) Have students share their illustrations; ask them if they were able to distinguish stars from planets. Explore/Explain 1. Students will be challenged to find Mars in the night sky and carefully track its motion over the coming months. To be most effective, students should start observing Mars in early January and continue to map its position until mid May. Once they find Mars, their observations will only take a few minutes each time and can be done once every one to two weeks. The exact nights of their observations are not very important so this activity should be easy to schedule. Cooperative learning strategies can link students and parent/caregivers to facilitate coverage during this time. The more "data points" gathered, the more "robust" the results. 2. Project transparency of Star Chart A onto screen and explain that this view of the stars in the Eastern sky will appear about 10 p.m. in mid-January. Point out the constellation Leo, along with its bright star Regulus. Point out that Leo's head and front quarters look just like a "backwards question mark" while his hind quarters and tail are marked by a triangle of stars. 3. Hand out copies of Star Chart A along with pieces of red cellophane. (The red cellophane is to be taped over the end of a flashlight. Red light will allow them to see their chart in the dark, but still allow their eyes to retain "night vision.") Their assignment over the next few nights is to go outside with their star chart and flashlights and find Leo in the sky, using the following procedure: Wait outside about 5-10 minutes before looking for Leo, allowing their eyes to adjust to the dark. After locating Leo, they should look for a bright point of light in this part of the sky that is not on their star chart. This should be Mars! Mark the position of Mars on their star chart as accurately as they can; date their observation. (Share success stories and frustrations in class.) 4. During the first class period after students have successfully located Mars in the night sky, project transparency of Star Chart A again and have students confirm their observations. (Mars will move very little from one night to the next.) 5. Pass out Star Chart B; ask students to compare Star Charts A and B (B is more detailed and shows a smaller part of the sky than A). Have students carefully mark the position of Mars on Chart B with a dot and, next to it, write a small number 1 and the date.

Mars, Models and Math Mars comes closer to Earth than any planet except Venus. Thus, at times, Mars can become as bright or brighter than the brightest stars. Mercury, Venus, Mars, Jupiter and Saturn were all known to ancient watchers of the sky. While they looked just like stars, these five objects were regarded as special because, from week to week, month to month, they slowly moved against the background of the stars as if they had special powers. (Our word for these objects, planets, derives from an ancient Greek word meaning "wanderer.") Why the planets appeared to move against the fixed stars remained a mystery to the ancients. To some, the planets were gods, shrouded in mystery, but to be worshipped. Others tried to create mental pictures, or models, of the universe that explained their movement. One popular notion (suggested by the Greek philosopher Aristotle, 384-322 B.C.) was that the Earth was in the center of the universe and that all objects in the heavens revolved around the Earth. Planets, along with the Sun and Moon were imagined to be carried along on crystal spheres, nested one inside the next, with the Earth at the center. A final sphere, containing the stars, encased all the rest. As the spheres turned at different speeds, the various celestial objects were seen moving across the sky. Mars, however, as well as Jupiter and Saturn, posed a serious problem. From week to week, these planets would normally move eastward against the stars. But once in awhile, they would stop in their tracks, appear to reverse direction, and move westward for awhile. This was called backwards, or retrograde, motion. Then, they would stop again and resume their easterly trek. Some ancient astronomers (including Ptolemy who lived in the second century A.D.), cleverly explained this odd planet behavior by suggesting that these planets were actually attached to little sub-spheres that, in turn, were attached to bigger spheres, the original "wheels-within-wheels" concept. As they rotated on these little spheres, revolving around Earth on their larger spheres, these planets would periodically undergo their retrograde motion. Though complex, this idea actually permitted accurate predictions of planetary motion. It was, however, completely wrong. In 1543 a Polish astronomer, Nicholas Copernicus, showed that Ptolemy's complicated picture of the universe could be made simpler (and the little circles eliminated) if the Sun was in the center of the system rather than the Earth. Now the retrograde motion of Mars (and the other outer planets) could be seen as a consequence of the Earth periodically passing these planets by as it rounds the Sun at a faster speed. Activity 2.1 allows your students to recapitulate thousands of years of history by observing the night sky, noting Mars' distinctive motion, and deriving the explanations first articulated by Copernicus and then elaborated by Johannes Kepler and Galileo Galilei. Mars fascinated all of them--now it's your students' turn.

6. Students should continue their own MarsWatch once every one to two weeks (you may want to suggest certain nights if the weather forecast calls for clear skies), each time marking Chart B with another dot and number and noting the date in the table. Each week you can have a group discussion and make a master chart with the planet's average position based on all the student observations. As the weeks go on, discuss the changing position of Mars amid the stars with the students and ask them if--as a by-product of their sky-watching--they also notice any difference in the time that Leo appears in the Eastern sky. (Note: as the Earth continues to orbit the sun, Leo will rise a little earlier each night and thus appear to be higher and higher in the sky at the same Earth time from week to week. This also means that students can make their observations earlier and earlier as the weeks go on.)

Over time, the students will see that Mars moves among the stars in an apparently peculiar way--performing a loop-the-loop as shown in Diagram 1. As Mars is seen to reverse direction, move backwards among the stars and finally reverse direction again, discuss this strange heavenly doh-see-doh with your students. Explain that this strange behavior (technically known as "retrograde motion") really puzzled astronomers until the 16th century.

At the appropriate point in the semester, remind students of their earlier simulation of the Earth/Mars orbit in the school field or playground. Then pass out copies of Diagram 1 and explain that the marked positions of Earth and Mars show corresponding positions for the two planets on the dates given. Have students draw lines connecting corresponding images of Earth and Mars and extend these to the distant stars as shown in your teacher's copy of Diagram 1 in the Teacher Materials. Discuss with students how the apparent loop-the-loop motion of Mars is merely an illusion caused by the Earth passing Mars by as it orbits the sun. (By analogy, a car that you overtake on a highway may look like it's going backwards relative to you).

In addition to observing Mars with the unaided eye, see if you can help the students observe Mars in a telescope. If the school does not own a telescope, try contacting your local planetarium, college or amateur astronomy club. A class visit can be arranged or your local amateur astronomers may be persuaded to bring telescopes to the school.

Have students look at Mars through the telescope(s). Using their red-gelled flashlights and several blank, three inch circles drawn on white paper, have them carefully sketch what they see and make note of any apparent color of the planet and any individual features they can see. In a follow-up class, compare the sketches and colors. Discuss similarities and differences between the students and the reasons for the differences. Post the best (or most amusing!) observations to the Live From Mars project and we'll place them on-line, as motivation to others, and documentation of your students participation in MarsWatch '97. (NASA JPL's plans call for major involvement from Europe and Japan as well as North America, so your students will be participants in a broad, international effort.) Draw students into a discussion of what can be seen of Mars through telescopes from Earth given variations in "seeing" conditions from place to place and day to day, the subjective nature of human eye-brain coordination, and the value of using electronic instruments on board spacecraft in Earth orbit (such as the Hubble Space Telescope) or, better yet, in orbit around Mars itself.

Expand/Adapt/Connect Students with regular access to telescopes may wish to systematically make a Map of the entire surface of Mars as it appears during the late winter and spring of 1997. Because Mars rotates once every 24 hours and 37 minutes (which makes a "Martian day" or "sol"--for Sun), a map can be made by combining drawings completed every few nights for a period of about a month. Gaps due to prolonged inclement weather can be filled in the following month and, over several months, seasonal changes on Mars can be observed, such as the growth or shrinking of a polar cap or a change in the brightness of surface features. Note: Due to the tilt of Mars toward Earth at this time, students will be viewing the physical features of the Northern hemisphere. Maps of Mars showing polar caps and prominent light and dark features will be available on the Live From Mars Web Site so students can compare their drawings. Using your students' observations, or downloading others from on-line, create a "flipbook" that lets you set Mars in motion. (This will be only as smooth as the underlying observations permit, but if you use a standard star chart for all students, you should get an interesting result. You and your students may even want to experiment with "reducing data", literally kicking some data points out of your series in order to arrive at a better animation.) Go On-line via the LFM Web Site, and check out Mars Today and you'll find computer graphics showing Mars' relative position to Earth, a depiction of what face of Mars is facing Earth that day... even a weathercast! Advanced students might even want to capture some of these images, and if time, talent and disk-space permit, make their own time-lapse movies. View Cosmos, Program 5, "Blues for a Red Planet", in which astronomer Carl Sagan reviews how "seeing" led many 19th Century astronomers to detect canals on Mars. (This program also provides an overview of the Viking findings.) Have students investigate some of the lore than surrounds the planet Mars, including Percival Lowell's belief that Mars had canals and an advanced race of beings; H. G. Wells, The War of the Worlds; Orson Welles' radio broadcast of War of the Worlds; novels about Mars by Edgar Rice Burroughs. Have them write a short story about a fictional Mars from these more romantic ages. (A good, easy source for both literature and the 1934 radio broadcast is the Visions of Mars CD-ROM, produced by The Planetary Society: see MultiMedia Resources) Ask students to make believe that they are a member of the first human crew to travel to Mars and ask them to write about their experiences. Suggest their writings take the form of a short story, a personal diary or log, a collection of illustrated poems or a combination of these. Hold an art contest in which students create works related to Mars. Paintings, sculptures or other forms of expression may relate to Mars as fact or fiction.

Astronomy Clubs Teachers who are not as comfortable with "eyes-on" astronomy activities or who live close to urban areas where outdoor astronomy activities are precluded by light pollution are encouraged to contact their local amateur astronomy club. (see the LFM On-line pages under Featured Events and Resources for more information.) Ask a volunteer astronomer, amateur or professional, to visit your classroom to teach your students about Mars' retrograde orbit. Your district may also have, or be able to borrow a Starlab (an inflatable plastic dome and mini-planetarium projector) to simulate night sky watching activities. (See also MultiMedia Resources for suggestions about CD-ROM and other software that can bring the night sky, digitally, to a desktop near you.)

Suggested URLs
http://marswatch.tn.cornell.edu/mars.html
http://www.skypub.com/