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Challenge Questions

Classroom Responses

>>>>>>>>>>Week #3 Challenge Question RESULTS <<<<<<<<<<
THE PARTICIPANTS THIS WEEK: A BIG THANKS to the following classes and individuals who participated in Challenge Question Week #3: David Rajan (California) Thabet Al Fishawi (Egypt) Florian Breuer (South Africa) Sean Masterson Matt Krell (Mississippi) David Press (California) Michael McVey's HS Class (Arizona) Jeff Hill (Utah) Oirand Floresca John Bayne (Australia) Mr. Grott's Class (New York) Brian Grigsby's Class (California) The Students of Blessed Sacrament School (Washington, DC) Philip Gressman (Missouri) Mike Reynolds' Class (Michigan) Edward Beidas' HS Class (Illinois) Norma Barnes' Seventh and Eighth Graders (Missouri) Cathy Peterson Fifth Grade Class (California) Janet Cook's Alternative HS Class (Colorado) Charlotte Steven's 8th Grade Class (Georgia) Tim McCollum's 8th Grade Class (Illinois) Dr. Thomas Keens (California) Mrs. Heine's 5th Grade Class (Florida) John Herrold - 9th Grade Class Mark Hines' Class (Hawaii) Monticello Schools 5th Grader Jake Argo (Wisconsin) Robert Moncello THE BEST ANSWERS WERE GIVEN BY THESE PARTICIPANTS: There were so many participants who explained the solution correctly that we were really impressed with your problem-solving skills. The BEST explanations were selected based on clarity and accuracy. High School Level: Philip Gressman, HS Senior at Ava, Missouri Middle School Level: Jerry Trammell, 7th Grader Cranbrook Kindswood MS, Bloomfield, MI Elementary Level: Mrs. Heine's 5th Graders, Palm Bay, Florida (second answer) CONGRATULATIONS TO ALL!! THE REAL WINNERS = EVERYONE WHO GAVE THEIR BRAINS A WORKOUT TRYING TO SOLVE THIS PUZZLER! Thanks to ALL of YOU. We are glad to see adults and college-level students involved and participating just for fun! ********************************************************* COLLATION OF ALL ANSWERS RECEIVED: -------- Bob To: jwee@mail.arc.nasa.gov Subject: Challenge Question #3 The reason that Deimos appears to move from east to west in the Martian sky is due to the fact that Deimos orbits Mars faster then Mars rotates. On the other hand the reason Phobos seems to move from west to east is because its orbit is slower then the rotation of the planet; this is what gives the illusion that the moon is moving backwards. For example: imagine you were watching a race from the middle of the race track, as you spun counterclockwise (from right to left) to keep an eye on the lead car the other cars would seem to be moving off to your right (from the left to the right). We all know however that the cars do not really change direction; they just appear to be because they are not traveling as fast as the lead car. Robert J. Moncello --------- David Rajan Reply-To: kiwiman@ix.netcom.com To: jwee@mail.arc.nasa.gov Subject: CHALLENGE QUESTION Just a quick guess on the Mars moon question. Does it have anything to do with parallax, or maybe does one of the moon's speed so that when it rotates, you don't see it rotating in the proper direction so that during every interval you see it, it is in the opposite direction of its rotation, giving the appearance of its moving backwards? I don't really know how to explain this, but is it similar to the way stagecoach wheels turn backwards in movies (because of the camera's shutter speed, because the movie camera displays 24 frames/sec so that every one 24th of a second, the spoke's position is counterclockwise to the position it was in the frame before even though it's moving clockwise? Whew! I'm not sure if it's even remotely right, but is it a valid guess? David Rajan, senior at Bishop O'Dowd High School in Oakland, CA ---------- Thabet Peter Al Fishawi To: jwee@mail.arc.nasa.gov Subject: CHALLENGE QUESTION Dear JAN That is because Deimos have a realtivly long orbital period (1.26 days)in comparrison with Phobos , so if we liken Deimos to our moon, they both rotate from east to west, and that is not due to their motion but due to the rotation of the planet "Earth or Mars," while Phobos has a very short orbital period (0.32 days) so it's movment across the sky is its real motion in the space, which is from west to east like any other moon. Thabet Al Fishawi I'm in 2nd year secondary. I live in Cairo, Egypt. ---------------- From: "MNR. F BREUER" Hi! Here is my brief answer to challenge question #3, Both moons orbit Mars in the same direction, but, because of the different distances from Mars, they orbit at different speeds. Mars itself is rotating in the same direction, with an angular velocity that is in between the angular velocities of the two moons' orbits. So that means that while the one moon (I don't know which one, doesn't matter) is orbiting in one direction, the martian surface is rotating away faster under it, so to the observer on the surface the moon appears to be moving backwards. The other moon, however, is orbiting faster than the surface (expressed informally) so it "overtakes" the surface and thus an observer on the surface sees this moon moving forwards. That was somewhat informal. By speeds I actually meant angular velocities. Cheers, Flo. (Florian Breuer, 2nd year math student at the University of Stellenbosch, South Africa) ------------ Masterson, Sean Subject: RE: CHALLENGE QUESTION Date: Mon, 4 Nov 1996 01:54:45 -0800 >CHALLENGE QUESTION #3: MOONS OF MARS Well, I don't know the length of a Martian day or the orbital periods of either moon, but the apparent retrograde motion must be due to Phobos moving more slowly than the speed at which Mars rotates and Deimos moving more quickly. When you give out the correct answer, could you explain whether there would be a way for an observer on the surface of Mars to prove that the two moons travelled in the same direction? Many thanks. ----------- mitch krell To: jwee@mail.arc.nasa.gov Subject: Challenge Question#3 My answer is as follows: While the two moons orbit Mars, Mars is also rotating. As the motion of the two moons is retrograde (opposite) to that of Mars, Mars rotates faster than the farther moon, thus causing it to appear to move with Mars's rotation Matt Krell, Hattiesburg, MS 8th Grader (participating on his own) ----------- Dave Press To: jwee@mail.arc.nasa.gov (Return requested) Subject: CHALLENGE QUESTION CHALLENGE QUESTION #3: MOONS OF MARS Here is a new puzzler for this week: Mars has two moons: Deimos and Phobos. If you stood on the surface of Mars and looked up into the night sky, you would see Deimos slowly travel from east to west across the sky while Phobos would be slowly traveling from west to east. In other words, the two Martian moons travel in opposite directions across the Martian sky. Yet both moons actually orbit Mars in the same direction. Explain this apparent paradox. My guess is that the angular velocity of Phobos' orbit is less than the angular velocity of the planet's rotation and that this would make the moon appear to be traveling backwards with respect to the planetary surface. David Press (college junior who is participating just for fun!) Los Angeles Pierce College Woodland Hills, California ------------ Michael McVey Subject: Challenge Question (Mars Moons) Martian Moon Question Chisa Valdez (Grade 9) and Karla Curiel (Grade 9) of Desert View High School make the following submission: If one of Mars's moons has an orbit that is slower than Mars's speed of rotation and the other moon has a faster orbit - then one moon would appear to move opposite the other. Desert View High School Teacher: Michael McVey, mmcvey@ccit.arizona.edu ------------ Alan & Cath'e Troyer" Subject: CHALLENGE QUESTION The reason it appears that the Martian moons Phobos and Deimos are traveling in different directions is because the rotation of Mars is greater than the revolution of Deimos, making the appearance that Deimos is traveling in the opposite direction, while Phobos' revolution is greater than the rotation of Mars. Jeff Hill, age 17 Salt Lake City, Utah -------------- Floresca, Oirand C." <09619755@mail2.dlsu.edu.ph> Subject: CHALLENGE QUESTION Mars rotates counterclockwise from its axis. If you would look to the two moons Deimos and Phobos on Mars you would see Phobos travelling from west to east and Deimos from east to west. You see this because Phobos is in a higher orbit than Deimos. Therefore it would only take Deimos a short time to orbit Mars while Phobos would take a little bit longer. Even though they revolve around Mars in the same direction, which is to the west, Phobos would look like it is travelling from east to west because it could not keep up with the rotation of Mars and the revolution of Deimos. --------------- John Bayne Subject: CHALLENGE QUESTION If you were to look at Phobos and Diemos from Mars, the reason you would see them moving in opposite directions, even though they are travelling the same way, would be that Mars is rotating faster than one, and slower than the other. Therefore, comparitively, Mars would be "overtaking" one moon and would be "overtaken" by the other. John Bayne, 15-year old, in grade 10 at Saint Augustine's College, Cairns, Queensland, Australia. ----------------- Dave Grott Subject: Challenge Question #3 - Mr.Grott's Class We calculated that Phobos is only 3750 miles above Mars and will eventually crash into the surface. Deimos is 12500 miles above the surface. It orbits Mars every 60 hours while Phobos orbits Mars 3 times per Martian day. We labeled East and West on the blackboard. Danielle volunteered to be Mars the Planet and our observer on the surface. Patrick was Deimos. He did not move because it takes 60 hours to complete one rotation. Tim was Phobos because Phobos orbits every 7 hours and 39 minutes. He ran, and ran, and ran around Danielle. As Tim moved Danielle was able to see Tim with her left eye and then her right eye, the left being west and the right east. Phobos appears to rise in the west because it is so close to the surface and travels so fast. Mr.Grott's Class Alden Place Elementary School Millbrook, New York Dear Jan Wee; We found the question too challenging but we enjoyed solving it. We had a problem because your data was not accurate. Phobos travels faster than you stated. Timing for the observation is critical. Deimos moves like the needle on a gas gauge, basically we ignored your data and used our own. Mr.Grott's Class ---------------- bgrigsby@shasta-co.k12.ca.us (Brian Grigsby) Subject: CHALLENGE QUESTION My students, Troy Goddard and Briar Clements, had the following answer to Challenge Question #3: Even though the moons appear to travel in opposite directions, the rotation of Mars is such that it rotates faster than Phobos orbits around it, thereby causing the appearance of the moons to orbit in opposite directions. Brian Grigsby Shasta High School 2500 Eureka Way Redding, CA, 96001 bgrigsby@shasta-co.k12.ca.us ----------------- science@sysnet.net Organization: Blessed Sacrament Answer to Challenge Question of October 28 1996: The way it works is that Deimos and Phobos are different lengths from Mars along with both orbiting at different speeds. Deimos travels once around Mars in a day while Phobos travels twice around Mars in one day. That means if you look up from Mars you will see Deimos going one way and Phobos going the other way. From: Jonathan, Robert, Lydia, and Joe Blessed Sacrament School ----------------- science@sysnet.net Organization: Blessed Sacrament Our Answer: The reason why the moons Deimos and Phobos appear to travel in opposite directions is that the two moons travel at different speeds. The one planet that travels faster is probably closer to Mars. The closer you get to a planet, the more the gravitational pull is, so this explains the faster speed. The second moon orbits farther away from Mars, so its orbit speed is slower. This slower speed makes it look like it is travelling backwards compared to the other moon. However, as stated in the question, both moons are travelling in the same direction. >From team 5 at Blessed Sacrament: Devin Delany, Tara Quinn, Andrew Latimer and Teddy Rykowski ----------------- science@sysnet.net Organization: Blessed Sacrament Subject: Challenge Question # 3 Our Answer: Mars is rotating to the right at a certain speed. The moons, Phobos and Deimos, are both orbiting around Mars to the right. One of the moons is going much faster than the other. The slow moon is going even much slower than Mars is rotating. If one were standing on the surface of Mars, one would see the faster moon "rising" in the right, as it would appear to do. At the same time Mars would continue rotating at the same speed causing it to catch up to the slow moon. It would continue going faster than the moon causing it to look like it was "rising" from the left as one stands on the surface of Mars. This apparent paradox is called relative motion. >From team 6 at Blessed Sacrament: Jodi Paci, Robert Yator and Portia Mills -------------- science@sysnet.net Organization: Blessed Sacrament Subject: Challenge Question I think that the reason that the moons appear to be going opposite ways when they are really going the same way is that one moon is moving faster than the other giving the illusion that one is going back and one is going forward. By Tim Warren Deborah Berhane Virginia Di Tata Lesley Seidensticker -------------- science@sysnet.net Organization: Blessed Sacrament Subject: challenge question The moons just appear to be traveling east to west. But they are really going the same way at the same time. By Ginny Garayta and Jason Leshner -------------- science@sysnet.net Organization: Blessed Sacrament Subject: Challenge Question #3 A number of things happen to provide this illusion. First, 1 moon is orbiting around Mars at a greater speed than Mars is rotating. The other moon is orbiting slower than Mars is rotating. So it seems that the slower moon is moving in the opposite direction from the faster moon. Danny Ross Chris Hayes Maureen Andary Julie Finelli -------------------- science@sysnet.net Organization: Blessed Sacrament Subject: Challange Question #3 Our team thinks that this illusion is caused by the planet Mars rotating on its axis at slower speed than one moon and the other moon orbiting around Mars faster than it can rotate. Mike Minchik Sarah Reaman Greg Borsage --------------------- science@sysnet.net Organization: Blessed Sacrament Subject: Challenge Question #3 Each moon is on one side of Mars. Their orbit around Mars is elliptical so each moon goes around trailing the other. If you are wondering why you never see one going the other direction is because the orbit of Mars is faster then the orbits of the moons, making your sight of them the same all year around. Alexis B. Monty B. Kristen T. Ezra .D ---------------------- Philip Gressman <102470.1167@compuserve.com> Subject: Challenge Question #3: Moons of Mars This situation can be likened to a three-man race around a circular track. From the stands it is easy to see that all three runners are traveling in the same direction around the track. However, the view would be quite different for the second-place runner. He would see the first place runner pulling farther and farther ahead while the other runner lags farther and farther behind and, hence, appearing to be going in the opposite direction of the lead runner. Mars's angular velocity of rotation is slightly more than the angular velocity of revolution for Deimos and less than Phobos's velocity of revolution. Therefore, as Phobos travels slightly faster than Mars rotates, it will appear to "pull away" and move from west to east. Dimos, moving slightly slower than Mars is rotating, will appear to "lag behind" or move from east to west. Philip Gressman, HS Senior from Ava, Missouri --------------------- Mike_Reynolds_at_CEC001-FA@cc.cranbrook.edu Subject: challenge question If a man was standing on Mars and he was looking up at the moons he would see that Deimos travels from east to west and Phobos travels from west to east for a few reasons. One that Deimos is farther away from Mars than Phobos. This means that Phobos revolves around Mars a lot faster than Deimos. But the key is that Phobos also revolves faster than Mars rotates and Deimos revolves slower than Mars rotates. The rotation of Mars is 24.6229 hours, Phobos revolves around Mars in 7.6 hours, and Deimos revolves around Mars in 30 hours. Therefore Phobos would appear to travel from west to east because it is going faster than Mars rotates. Deimos would appear to be traveling east to west because it is going slower than Mars is rotating. Mike Reynolds - 7th grade science teacher at Cranbrook Kingswood Middle School, Bloomfield Hills, Mi. Our response to challenge #3 was sent in by Jerry Trammell, 7th grade. ------------------------ Darlene Taylor Subject: Challenge Question #3 We are a MESA class at Dixon Middle School in Provo, Utah. Our PTK advocate is Mel Twitchell in Utah. Our answer: >From Mars the moons are seen to move in opposite directions. This is because Phobos takes less time to revolve once around the planet Mars than what Mars takes to rotate on a daily basis. While Deimos takes a few hours more to revolve. --------------------- Edward Beidas Subject: answer to CHALLENGE QUESTION #3 Answer to question #3 Phobos is very close to its planet, Mars. In fact, it is so close that it takes less time to circle the planet than the planet takes to revolve on its own axis. This accounts for the moon's rising in the west. Deimos revolves in a period of time very close to the rotation of Mars. Therefore, it seems to be rising in the east as does our moon on Earth. This explains why even though both moons orbit the planet in the same direction, Phobos seems to rise in the west and Deimos in the east. PROVISO EAST HIGH SCHOOL --------------------- Norma L. Barnes Challenge Question 3 Seventh Grade Phobos revolves around Mars slower than Mars rotates, and Deimos revolves around Mars faster than Mars rotates, so Phobos appears to be going backwards. ----- Eighth Grade One of Mars's moons, Deimos, is faster than Phobos which rotates one-third as fast as Mars. This gives the illusion that Phobos moves from west to east while Deimos is farther away from Mars, but still moves from east to west. Strafford Middle School Norma L. Barnes nbarnes@mail.orion.org ----------------------------- cpeterso@mail.valverde.edu Maybe one of the moons works like a mirror and it reflects other things against the sky to make it look like they are going two different ways. From Desmond Clark Both of the moons are going around Mars, but one moon is rotating right and the other moon is rotating left. From Joseph Gutierrez Both moons go the same way, but it looks like they're going separate ways because one is above the other. From Jorge Flores Mead Valley Elementary School in Perris, CA. Fifth-grade class Cathy Peterson ---------------------- Date: Fri, 8 Nov 1996 23:23:53 -0800 I put the challenge question up to my space meteorology class. They came up with: "There must be a problem between the rotation of Mars and revolutions of the moons." After we made a model using a couple of globes and my drink container, we decided the backwards moving moon must be revolving slower than Mars rotates, while the normal moving moon must be revolving faster than Mars rotates. Hope this is close. Thanks for the good opportunity to cause some thinking! Janet Cook (HS Class) _____________________ Charlotte Stevens Subject: Challenge Question #3 I got a variety of responses from my students about the moons of Mars: Evan writes - "One moon goes faster than the other so it looks like they are going in opposite directions, but it is just passing the other moon." Vera says - "Both of the moons could be moving west to east, but their orbital route may be off slightly, which makes the moons' track crisscross. Mars is much smaller than Earth so it separates more on its track because Mars is more smaller. So if you're standing on the surface, they look like they're moving in opposite dirctions, but from Earth it looks like they're moving in the same direction." Charles' guess - "Because the way Mars moves. I'm guessing Mars moves in a slanted circulation. So the moons move and crisscross or clash with each other. The moons also probably move at different speeds." Caroline states - "Mars' two moons are opposite from each other. Since Mars is a smaller planet, the curve is more than Earth. If you stand under one moon going one way you might be able to see the other moon across the sky going the other way following it." from Alison - "The planet is making its way around the sun, so as the planet turns you would think the planets were moving in different directions. The moons follow each other across the sky. You would see the moons at different times, going the same way. Or, if you stand on the North Pole and look one way you'll be watching it go from east to west, but if you turn around it will appear to go the other way." Kelly's answer - "Deimos and Phobos, Mars' two moons, travel around Mars' surface at different distances - one is higher than the other. They both have their own orbit systems so that way they can't crash into each other. This is because of Mars' gravity." Dave, Michael, Sang, Ashish, Marissa and Aracelis all agreed it was the speed of the moons - "One moon is moving faster than the other moon so it gets farther and farther away from the other moon, so it looks like they are going in opposite directions. ...they would in a way follow each other..one moon is traveling the opposite way that Mars is rotating...Mars is rotating faster than the speed of the moon orbiting Mars. But it is also faster than one of the moons. So it seems as if the moon is going the other way because Mars is spinning faster than one of them." Charlotte Stevens 8th grade teacher Taylor Road Middle School Alpharetta, Georgia USA ----------------------------- cxtdm@eiu.edu (Tim McCollum) Subject: Challenge Question One moon revolves around Mars slower than Mars rotates. The other moon revolves around Mars faster than Mars rotates. So when you stand on the surface of Mars you would see one moon move from the east and set in the west because the rotation of Mars passes the moon. The other moon rises in the west and sets in the east because it passes up the rotation of Mars. They are actually going the same direction. Michael Lawhorn, 8th grade science Mr. McCollum's class Charleston Junior High School Charleston, IL ---------------------------- KEENS%smtpgate@chlais.usc.edu> (Tom Keens ) Subject: Mars Team Online - CHALLENGE QUESTION. Date: Fri Nov 8 17:28:29 1996 CHALLENGE QUESTION: Mars has two moons, Deimos and Phobos. If you stood on the surface of Mars and looked up into the night sky, you would see Deimos slowly travel from east to west across the sky, while Phobos would be slowly traveling from west to east. In other words, the two Martian moons travel in opposite directions across the Martian sky. Yet both moons actually orbit Mars in the same direction. Explain this paradox. ANSWER: I am not an astronomer with ready access to the data to back this up. However, it would appear that the only explanation would be that both moons orbit Mars in the same direction as Mars' rotation. Mars must rotate faster than Phobos, thus it lags behind your position on the surface of Mars, appearing to move "backward" (west to east). On the other hand, Mars must rotate slower than Deimos, thus it gradually gains position relative to your position on the surface of Mars (east to west). Thank you. ---Thomas G. Keens, M.D. Childrens Hospital Los Angeles ----------------------------- Subject: Challenge Question Our class reviewed Earth's moon and then used students to be Mars and the two moons and demonstrated their orbits. We also did a one Mars day self demo by using one hand for Deimos and the other for Phobos and the person as Mars. If you start Deimos with your right hand extended across your body to the left and gradually make one complete turn allowing your arm to only turn 3/4 of the way this simulates Deimos. In the meantime take your left hand with bent elbow and make three circles around your head to show Phobos' orbit at the same time. You can see the direction of movement as Mars. After these exercises students wrote their explanations. This is a combination of two. Explanation by Robby Wagner and Emily Hoffman, fifth graders at Lockmar Elementary, Palm Bay, FL The reason it looks like one moon is going one way and the other is going another is their speeds. Phobos goes around Mars very fast in 7.7 hours. In one Mars day (24.62 hours) Phobos goes around Mars three times. It goes from west to east. Deimos goes slow (30.3 hours). Deimos is so slow it looks like it goes east to west. It doesn't go completely around Mars every day. Our class really enjoyed this. Thanks. Mrs. Heine and the Fifth Grade GSP at Lockmar Elementary, Palm Bay, FL heinee@mail.firn.edu ---------------------------------- John Herrold Subject: Martian Moon Challenge Question Re: CHALLENGE QUESTION I had my ninth grade students respond to the question regarding the apparent backwards motion of Deimos as seen from the surface of Mars. Of many entries, these two seem to be the best! >From LISA BLAKE: Planets really move from west to east. Deimos and Phobos may both be moving slowly but Deimos is moving slower than Mars and Phobos is moving as fast or faster than Mars. That is why Deimos looks like it is moving backwards (from east to west). Deimos's orbit is most likely outside the orbit of Phobos and that is another reason why it is moving slower (the orbit is bigger). Lisa Blake EP4 >From MAEVE GLEASON: Deimos' orbital period is 1.26244 days. Mars rotates on its axis faster so Deimos appears to move backwards in a retrograde motion from the Martian surface. On the other hand, Phobos has an orbital period of 0.31891 days which means an observer on Mars would see the moon rise twice on a single day because it moves much faster than Mars rotates. Maeve Gleason EP4 John D. Herrold Science Department, Grosse Pointe North High School jherrold@www.science.wayne.edu ----------------- mhines@aloha.com Subject: CHALLENGE QUESTION #3 Mars moons (fwd) By way of: Mark Hines Mid-Pacific Institute mhines@hawaii.edu 2445 Kaala Street tel (808)-973-5000 Honolulu, HI 96822 fax (808)-973-5099 From: Christi Seto To: mhines@hawaii.edu Subject: bonus:mars moons Hi Mr. Hines Here's an attempt to explain the movement of Mars's moons. If Mars is rotating counterclockwise, and Deimos appears to be moving from east to west across the sky and Phobos appears to be moving from west to east across the sky when in fact the two moons are going in the same direction, then it means that Deimos is orbiting Mars at a faster rate than Mars is rotating and Mars is rotating at a faster rate than Phobos is orbiting Mars. Therefore, the two moons appear to orbit Mars in opposite directions when they really aren't. Christi Seto From: Arron Yoshida To: mhines@hawaii.edu Subject: moons Wait. I have an improved answer. They are all rotating in the same direction so maybe one moon travels faster than the rotation Mars and maybe the other moon travels slower than the rotation of Mars so it would appear to be going in opposite directions. ------------------------- stmont01@llwisc.wecb.org (classroom account) Subject: Challenge #3 To: jwee@mail.arc.nasa.gov Challenge Question #3: This could happen if one moon is on one side and the other moon is on the other side of Mars, and then when they rotate at the same speed they seem to go in opposite directions. Also, Mars is tilted which allows you to see both moons. Jake Argo, grade 5, Monticello Schools, Monticello, Wisconsin.