pete@ctbilbo.UUCP (Pete Ritter) (11/06/90)
My collegues and I have been arguing about something. We would like an expert opinion about it. Does the Moon rotate about its axis (or any other) as it orbits the Earth? If a non geo-stationary orbiting body always presents the same face to the Earth, does it rotate about its axis (or any other) as it orbits? Does a geo-stationary satellite which always presents the same face to its primary rotate about its axis (or any other) as it orbits? Please email even if you post to the group. Thanks. ******************************************************************************* * Pete Ritter uunet!ctbilbo!pete | It tambu tru kaikai buai * * Communications Technology Corp. Dallas, Tx | na spet long makit. * ******************************************************************************* -- ******************************************************************************* * Pete Ritter uunet!ctbilbo!pete | Yu no can kaikai buai na * * Communications Technology Corp. Dallas, Tx | spet long makit. * *******************************************************************************
jabishop@uokmax.ecn.uoknor.edu (Jonathan A Bishop) (11/06/90)
pete@ctbilbo.UUCP (Pete Ritter) writes: >My collegues and I have been arguing about something. We would like >an expert opinion about it. >Does the Moon rotate about its axis (or any other) as it orbits the Earth? >If a non geo-stationary orbiting body always presents the same face to >the Earth, does it rotate about its axis (or any other) as it orbits? >Does a geo-stationary satellite which always presents the same face to >its primary rotate about its axis (or any other) as it orbits? In all of these cases, yes. If the body did not rotate (relative to the Sun), we would see the entire surface over the course of one revolution. We don't see the other side because the period of rotation in these cases is coincident with the period of revolution. Now, my question: Are the forces that synchronized the Moon's rotation and revolution the same forces that have nearly done so with Venus relative to the Sun? Does this phenomena only happen in a narrow band? -- jabishop@uokmax.ecn.uoknor.edu "Ground Control to Major Tom: Your circuit's dead; there's something wrong. Can you hear me, Major Tom?" -- David Bowie
mac@idacrd.UUCP (Robert McGwier) (11/06/90)
From article <129@ctbilbo.UUCP>, by pete@ctbilbo.UUCP (Pete Ritter): > > Does the Moon rotate about its axis (or any other) as it orbits the Earth? > Yes otherwise the moon (up to libration, nutation, etc.) would change its face to the earth. > If a non geo-stationary orbiting body always presents the same face to > the Earth, does it rotate about its axis (or any other) as it orbits? > A spacecraft in orbit without spin appears to rotate as it changes its position in orbit. The only way for a spacecraft in <ANY> orbit to constantly present the same face to you the ground based observer is to have a spinning. This spinning could get quite complicated if the orbit is not circular, not geostationary, and you are not at the center of the earth ;-). > Does a geo-stationary satellite which always presents the same face to > its primary rotate about its axis (or any other) as it orbits? > > Answered above. Bob -- ____________________________________________________________________________ My opinions are my own no matter | Robert W. McGwier, N4HY who I work for! ;-) | CCR, AMSAT, etc. ----------------------------------------------------------------------------
rick@ofa123.fidonet.org (Rick Ellis) (11/08/90)
On <Nov 05 23:52> Pete Ritter writes:
PR> Does the Moon rotate about its axis (or any other) as it orbits the Earth?
Yes, otherwise we'd see all sides of the moon.
--
Rick Ellis
Internet: rick@ofa123.fidonet.org
Compuserve: >internet:rick@ofa123.fidonet.org
BBS: 714 939-1041
--------------------------------------------------------------------------rmartin@clear.com (Bob Martin) (11/08/90)
In article <1990Nov6.010422.26534@uokmax.ecn.uoknor.edu> jabishop@uokmax.ecn.uoknor.edu (Jonathan A Bishop) writes: >pete@ctbilbo.UUCP (Pete Ritter) writes: > >Now, my question: >Are the forces that synchronized the Moon's rotation and revolution the same >forces that have nearly done so with Venus relative to the Sun? >Does this phenomena only happen in a narrow band? The Moon's rotation is locked to its orbital period by the tidal forces exerted upon it by the Earth. These tidal forces deform the moon so that it bulges directly towards (and dirctly away) from the Earth. If the moon were rotating at a different rate from the orbital period these bulges would rotate too. Since the bulge has mass, and would rotate out of the line connecting the center of the Earth with the Center of the moon there would be a very slight tug exerted on the Lunar bulge by the Earth which would tend to change the Moon's rotational velocity to be closer to the rate at which it revolves. This same effect is slowing down the rotation of the Earth and driving the Moon into higher and higher orbits. Very slowly of course. Venus must also experience tidal forces with the Sun and perhaps the it is the Sun's tides which have given Venus such a slow rotational period. But the story is more complex. Venus' rotational period is 243 Earth-days which is _longer_ than its 255 day period of revolution. Thus Venus' rotation is retrograde. There is circumstatial evidence indicating that Venus is tidaly locked with the _Earth_. I turns out that when both planets are on the same side of the sun, Venus presents approximately the same face towards the Earth. So it is possible that the Earth's meager (at that distance) gravity is in some way responsible for the small Retrograde rotation of Venus. Another interesting result of tidal effects is the vulcanism of IO. IO is the innermost moon of Jupiter, which would certainly be tidally locked to the planet if it were not for the influence of the nearby moons of Ganymede and Europa. These moons tug on IO and force it to continue rotating even against Jupiter's tremendous tides. This means that the tidal bulge of IO is continually dragged around causing IO to be alternately stretched and pulled. This causes frictional heating which has melted the interior of the moon and causes it to spew forth its innards in copious volcanic flows. -- +-Robert C. Martin-----+---------------------------------------------+ | rmartin@clear.com | My opinions are mine. They aren't anybody | | uunet!clrcom!rmartin | elses. And thats the way I want to keep it.| +----------------------+---------------------------------------------+
cyliax@ecn.purdue.edu (Ingo Cyliax) (11/09/90)
In article <1516.27389CA9@ofa123.fidonet.org>, rick@ofa123.fidonet.org (Rick Ellis) writes: |> On <Nov 05 23:52> Pete Ritter writes: |> |> PR> Does the Moon rotate about its axis (or any other) as it orbits the Earth? |> |> Yes, otherwise we'd see all sides of the moon. So is it common for moons to have the same axial rotational period as the orbital period, so that only one side is visibilty from the planet. If it is, what are the reasons for that ? -ingo -- /* Ingo Cyliax ECN, Electrical Engineering Bldg. * * cyliax@ecn.purdue.edu Purdue University, W. Lafayette,IN 47907 * * ing@cc.purdue.edu Work: (317) 494-9523 * * cyliax@pur-ee.UUCP Home: (317) 474-0031 */
marty@puppsr5.Princeton.EDU (Marty Ryba) (11/10/90)
In article <1990Nov9.083328@ecn.purdue.edu>, cyliax@ecn.purdue.edu (Ingo Cyliax) writes: |> So is it common for moons to have the same axial rotational period |> as the orbital period, so that only one side is visibilty from the |> planet. If it is, what are the reasons for that ? Well, a rather technical reference is Alexander, M. E. 1973, "Astrophysics and Space Science," v. 23, p. 459. He numerically models close binary systems and specifically the Earth-Moon system computing the time scales for synchronization of rotation and circularization of the orbit by tidal forces. A short and more readable paper is Press, Wiita and Smarr, 1975, "Ap. J. (Letters)," v. 202, p. L135. They concentrate on how to get strong viscosities in close binaries (stars), but give more readable formulae for tidal locking timescales. Eventually the Earth's rotation will be slowed to match the moon's. Tides dissipate rotational energy. Anyone with a rough number for the earth's mean viscosity??? -- Marty Ryba | slave physics grad student Princeton University | They don't care if I exist, Pulsars Unlimited | let alone what my opinions are! marty@pulsar.princeton.edu | Asbestos gloves always on when reading mail
EAO102@psuvm.psu.edu (11/11/90)
The moons WILL appear to rotate with respect to the sun, or if you are out side the Earth-Moon system. But rotation is taken with reference to the satell ite's primary, so I would have to say no. Inside the Earth-Moon system, the mo on doesn't rotate. The sun should not even be considered in the answer.