Teachers' Guide

Activity 2.1: Observing Mars in the Night Sky

Teacher Background The 1997 "Opposition Opportunity" The distance between Earth and Mars varies significantly as the two planets orbit the sun. Every 780 days, Earth and Mars have what--in cosmic terms--counts as a "Close Encounter." At such times, both planets are in a straight line with the Sun, and Mars is at its closest to the Earth. Mars rises in the East as the Sun sets in the West and the two planets are said to be in "opposition." However, because Mars' orbit is quite elliptical, the distance between Earth and Mars at different oppositions isn't always the same. It can be as little as 35 million miles (56 million kilometers) or as great as 61 million miles (98 million kilometers). In March 1997, the Earth and Mars will once again be in opposition. Mars will appear as a distinctive copper-colored, star-like object in the eastern evening sky that will be brighter than any of the stars around it. This will make it a relatively easy object for students to locate, identify, and track from week to week-while "their" spacecraft are en route to the very place they are observing from down here on Earth. At this time, Earth and Mars will be a little more than 68 million miles (109 million kilometers) apart, but surface markings should be clearly visible, even through moderate sized telescopes. These will include at least one polar cap, pinkish orange deserts and some of the other features which flashed upon the eyes of Schiaparelli and Lowell as they peered at the planet during the "Mars mania" of the late 19th Century. As Mars rotates on its axis, different portions of the planet will be seen from week to week, allowing students the opportunity to map the entire planet. And during the Spring semester here on Earth, seasonal changes can also be looked for on Mars, where it will be summer in the Northern hemisphere and winter in the Southern hemisphere. From early February through late April, Mars will also go through a very nice retrograde loop (see figure in Activity 2.1-Part 2) -making a loop-the-loop in the sky against the constellations of Leo and Virgo. Objectives Students will compare and contrast the orbits of Earth and Mars (duration, eccentricity, comparative distances from each other and the Sun), locate the planet Mars in the night sky, and observe and diagram its retrograde motion. Students will physically model the orbits of Earth and Mars and derive its characteristic retrograde motion from analyzing their observations. Materials 3 large circular signs, labeled (and appropriately-colored) Earth, Sun, Mars Star Chart A (one per student) teacher-made transparency of Star Chart A Star Chart B (one per student) teacher-made transparency of Star Chart B Diagram 1 (Earth and Mars orbit) (one per student) teacher-made transparency of Diagram 1 chalk or a spray can of "fake snow" a yard stick pencil a piece of red cellophane about three inches in diameter

Participate in "MarsWatch '97" Still more exciting is the opportunity for students to use this opposition as a chance to work with local amateur astronomers, or university researchers, as part of NASA's "MarsWatch 97" (see sidebar below) Bring an astronomer to your classroom, or take your class out to observe the Red Planet at night, using a larger telescope and more advanced techniques than suggested here. On-line you'll find the latest information about how to connect classroom and the often-enthusiastic amateur star-gazing community. Vocabulary constellation diameter ellipse opposition orbit simulation retrograde "MarsWatch'97" On-line For full information and updates on the activity, see the LFM Web Site (linked in via Featured Events and Teacher Resources)