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Model the Movements of the Planets In the Curriculum Starship Gaia Model the Movements of the Planets By Bob Albrecht and Paul Davis Subject: Science, math Audience: Teachers, teacher educators Grade Level: 5–10 (10–15) Technology: Internet/Web Standards: NETS•S 3, 5. NETS•T II, III. (Read more about NETS at www. iste.org—select Standards Projects.) Copyright © 2001, ISTE (International Society for Technology in Education), 800.336.5191 (U.S. & Canada) or 541.302.2777 (Int'l), 32 Learning & Leading with Technology Volume 28 Number 8 [email protected], www.iste.org. All rights reserved. Starship Gaia Table 1. Distances and orbital periods of inner planets from Sun. Data source: National Space Sciences Data Center Planetary Fact Sheets (http://nssdc.gsfc.nasa.gov/planetary/planetfact.html). Object Symbol Distance Distance Period Kilometers AU Earth days Sun 0 0.000 Mercury 57,910,000 0.387 88 Venus 108,210,000 0.723 225 Earth 149,600,000 1.000 365 Mars 227,920,000 1.524 687 Figure 1. Inner planets at 2001-06-13 UTC 14:00:00. Figure 2. Solar System Live settings (www.fourmilab.to/solar). uring our measurement and bital period of each planet, the number appearance of the diagram of the or- modeling adventures, we of Earth solar days (1 solar day = 24 bits and positions of the planets. D have modeled the relative hours) for the planet to make one com- We went to Solar System Live and sizes of the planets in the solar system plete orbit around the Sun. entered settings to obtain the diagram and the distances of the planets from To see where the planets are now in Figure 1. It shows the inner planets the Sun (Albrecht & Davis, 2000–01, or at any date and time you choose, relative to our observing site (38° 27' 2001). These models have been static go to Solar System Live (www. North latitude, 122° 43' West longi- models. As time passes, our scale model fourmilab.to/solar). In the first line tude) for the date 2001-06-13 and time planets do not move the way real plan- of the first paragraph, click inner UTC 14:00:00 (Coordinated Universal ets move. This time, we’ll model the planets to go to a diagram showing Time—2:00 P.M. in Greenwich, En- motion of the planets as they go around the orbits and current locations of the gland). This time is 07:00:00 (7 A.M. and around the Sun. To keep it simple, inner planets as seen by an observer Pacific Daylight Time). In this view of we’ll model only the inner planets: far above the North Pole of the sun. the inner planets, the planets are mov- Mercury, Venus, Earth, and Mars. Below the diagram is an area in ing counterclockwise. To change the The planets travel around the Sun in which you can enter the date, time, date and time to the ones you want, elliptical orbits. However, in the spirit and other settings. click the UTC button and enter the of keeping things simple, we’ll use cir- Farther down the page is an date and time. We also set the Size to cular orbits. The radius of each circular ephemeris showing such things as the 640 and the Orbits to Real. Our set- orbit is equal to the average distance of coordinates of the Sun, Moon, and tings are shown in Figure 2. the planet from the Sun. Table 1 shows planets relative to the observing site On June 13, 2001, at UTC the average distances from the Sun of on Earth. The observing site is at 47° 14:00:00 hours (2:00 P.M. in Green- the inner planets in kilometers and as- North latitude, 7° East longitude. wich, England), Mars will be in opposi- tronomical units (AUs). One AU is You can locate this site on Earth by tion to Earth. Mars will be on the op- equal to 149.60 million kilometers, the using a world atlas. Changing the lo- posite side of Earth from the Sun and average distance of Earth from the Sun. cation (latitude and longitude) of the you can draw a straight line through We’ll use AUs in our models of plan- observing site changes the data in the the centers of the Sun, Earth, and etary motion. Table 1 also shows the or- ephemeris but does not change the Mars. Mercury is catching up with Copyright © 2001, ISTE (International Society for Technology in Education), 800.336.5191 (U.S. & Canada) or 541.302.2777 (Int'l), [email protected], www.iste.org. All rights reserved. May 2001 Learning & Leading with Technology 33 Starship Gaia In astronomical lingo, a planet whose orbit is outside Earth’s orbit is a superior planet, and a planet whose or- bit is inside Earth’s orbit is an inferior planet. We would prefer outside planet and inside planet, but we’ll go with the standard jargon. An inferior planet can be at inferior conjunction or superior conjunction. It is at inferior conjunction when it is be- tween Earth and the Sun, and Earth, the planet, and the Sun are lined up in a straight line. An inferior planet is at superior conjunction when it is on the opposite side of the Sun from Earth, and the Earth, the Sun, and the planet are lined up in a straight line. At inferior conjunction, the Sun, Ve- nus, and Earth are lined up like this: ------- - At superior conjunction, Venus, the Sun, and Earth are lined up like this: ------- ------- --- Figure 3. Inner planets at 2001-08-05 UTC 22:00:00. A superior planet can be at conjunc- Earth and approaching inferior conjunc- around the Sun. How can you use Solar tion or opposition. It is at conjunction tion. Inferior conjunction of Mercury System Live to find the next date when when it is on the opposite side of the occurs when Mercury is between Earth Mercury will be at inferior conjunction Sun from Earth, and the Earth, Sun, and the Sun, and you can draw a to Venus? and the planet are lined up in a straight straight line through the centers of the Figure 3 shows the inner planets line. A superior planet is at opposition Sun, Mercury, and Earth. Mercury will on 2001-08-05 UTC 22:00:00. Mer- when it is on the opposite side of Earth be at inferior conjunction 2001-06- cury is at superior conjunction to from the Sun, and the Sun, Earth, and 16 UTC 13:00:00. You can enter this Earth. It is on the opposite side of the the planet are lined up in a straight line. date and time into Solar System Live Sun from Earth, and you can draw a and see a diagram with Mercury at straight line through the centers of At conjunction of Mars with Earth, inferior conjunction. Earth, the Sun, and Mercury. Com- Mars, the Sun, and Earth are lined up Venus was at inferior conjunction pare this diagram with the diagram in like this: 2001-03-30 UTC 04:00:00. Enter Figure 1, in which Mars was at oppo- --------------- ------- --- this date and time into Solar System sition. Earth travels faster than Mars, Live and see a diagram with Venus at so in Figure 3 it has passed Mars. On At opposition of Mars with Earth, inferior conjunction. Venus travels 2002-08-10 UTC 22:00:00, Mars the Sun, Earth, and Mars are lined up faster than Earth, so by June 13, it will be at conjunction relative to like this: has moved well past Earth. Remem- Earth. It will be on the opposite side ------- --- -- ber, the planets are moving counter- of the Sun from Earth, and you can clockwise in this view. draw a straight line through the cen- Of course, if you live on Mercury, all Mercury travels even faster than Ve- ters of Earth, the Sun, and Mars. En- of the other planets are superior planets, nus, so it will catch up with Venus, mo- ter this date and time into Solar Sys- and they can be at conjunction or op- mentarily be at inferior conjunction to tem Live and see a diagram with position relative to Mercury. If Venus is Venus, and then pass Venus and hurry Mars at conjunction with Earth. your domicile, Mercury is an inferior Copyright © 2001, ISTE (International Society for Technology in Education), 800.336.5191 (U.S. & Canada) or 541.302.2777 (Int'l), 34 Learning & Leading with Technology Volume 28 Number 8 [email protected], www.iste.org. All rights reserved. Starship Gaia planet, and Earth and Mars are superior Sun in the center of the page. We put planets. If you reside on Mars, Mercury, the paper with the orbits into a sheet Venus, and Earth are inferior planets. protector and drew the planet symbols on small dots that we can stick to the Planet Movement Models orbits. We got the diagram of the inner At Solar System Live, you can see where planets at Solar System Live, put it into Sun the inner planets are every day, once a a graphics processor, made a negative week, or as often as you want, so make image to get rid of the black back- a big poster of the orbits and attach ground, and printed it. Mercury small pictures or symbols of the planets On the printed copy, we drew hori- in their orbital positions. Every few zontal and vertical axes passing through days, move the symbols or pictures of the Sun and measured the angle that the planets to their current orbital posi- each planet made with the horizontal tions.
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