Murray.pa@XEROX.COM (02/18/86)
How do I tell which end is North and which is South? I assume that the "North" pole of Mars is the one that's pointing roughly parallel to the North pole of Earth. That doesn't transfer to Uranus very well.
holloway@drivax.UUCP (Bruce Holloway) (02/20/86)
In article <860217-235409-1418@Xerox> Murray.pa@XEROX.COM writes: >How do I tell which end is North and which is South? I assume that the >"North" pole of Mars is the one that's pointing roughly parallel to the >North pole of Earth. That doesn't transfer to Uranus very well. I think "North" probably means the pole that, when looking down directly above it, the planet seems to be turning counter-clockwise. Is this right? -- Bruce Holloway Digital Research, Inc. 60 Garden Court Monterey, CA 93942 ....!ucbvax!hplabs!amdahl!drivax!holloway (I'm not THAT Bruce Holloway, I'm the other one.)
jkw@lanl.ARPA (Jay Wooten) (02/20/86)
> How do I tell which end is North and which is South? I assume that the > "North" pole of Mars is the one that's pointing roughly parallel to the > North pole of Earth. That doesn't transfer to Uranus very well. In fact, it doesn't transfer at all since geological evidence shows that the Earth's magnetic poles switch places every few million years... Jay Wooten Los Alamos National Lab ARPA:jkw@lanl.ARPA
mink@cfa.UUCP (Doug Mink) (02/21/86)
> How do I tell which end is North and which is South? I assume that the > "North" pole of Mars is the one that's pointing roughly parallel to the > North pole of Earth. That doesn't transfer to Uranus very well. The International Astronomical Union, the final arbitter on the issue, says the the South pole is that which is below (South according to the Sun) the plane of the planet's orbit. Astronomers have traditional used the angular momentum vector (from the right hand rule) as the North pole. Using the IAU criterium, the sunward pole is South; using the traditional criterium, it is North. A confusing issue is that the North pole of the magnetic field is in the sunward hemisphere, though 55 degrees away from the sunward pole. When I had to refer to a point denoting the sunward pole in an illustration of a paper I wrote, I just called it "a pole of Uranus" in the figure caption (though on checking my reprints I note that it got changed to South somewhere along the line). -- -Doug Mink, aging hippy astronomer Harvard-Smithsonian Center for Astrophysics Cambridge, Massachusetts UUCP: mink@cfa.UUCP UUCP: {seismo|ihnp4|cmc12}!harvard!talcott!cfa!mink ARPA: mink%cfa.UUCP@harvvard.HARVARD.EDU
spock@iham1.UUCP (Ed Weiss) (02/21/86)
In article <860217-235409-1418@Xerox>, Murray.pa@XEROX.COM writes: > How do I tell which end is North and which is South? I assume that the > "North" pole of Mars is the one that's pointing roughly parallel to the > North pole of Earth. That doesn't transfer to Uranus very well. I believe you can define "North Pole" as: When looking at this pole from a position perpendicular to the plane of the equator, the planet has a counter-clockwise spin. This isn't anywhere near a precise definition, but you get the idea. -- Ed Weiss ihnp4!iham1!spock --> Live Long and Prosper <--
ethan@utastro.UUCP (Ethan Vishniac) (02/22/86)
In article <860217-235409-1418@Xerox>, Murray.pa@XEROX.COM writes: > How do I tell which end is North and which is South? I assume that the > "North" pole of Mars is the one that's pointing roughly parallel to the > North pole of Earth. That doesn't transfer to Uranus very well. The angular momentum vector of the Earth points toward the North Celestial Pole. Put it another way, looking down on the Earth from a point above the North Pole the Earth's rotation is counterclockwise. Therefore, by convention, the north pole of any planet is that pole from which the rotation appears counterclockwise. -- "Ma, I've been to another Ethan Vishniac planet!" {charm,ut-sally,ut-ngp,noao}!utastro!ethan ethan@astro.UTEXAS.EDU Department of Astronomy University of Texas
maariano@watdaisy.UUCP (Marco Ariano) (02/22/86)
In article <517@iham1.UUCP> spock@iham1.UUCP (Ed Weiss) writes: >In article <860217-235409-1418@Xerox>, Murray.pa@XEROX.COM writes: >> How do I tell which end is North and which is South? I assume that the >> "North" pole of Mars is the one that's pointing roughly parallel to the >> North pole of Earth. That doesn't transfer to Uranus very well. > >I believe you can define "North Pole" as: > When looking at this pole from a position perpendicular to the > plane of the equator, the planet has a counter-clockwise spin. > and: In article <287@drivax.UUCP> holloway@drivax.UUCP (Bruce Holloway) suggests: > >I think "North" probably means the pole that, when looking down directly >above it, the planet seems to be turning counter-clockwise. Is this right? > Looks to me like yet another case of the old 'Right Hand Rule'. Anybody (that knows what they're talking about) want to verify this?
dave@quest.UUCP (dave) (02/24/86)
> How do I tell which end is North and which is South? I assume that the > "North" pole of Mars is the one that's pointing roughly parallel to the > North pole of Earth. That doesn't transfer to Uranus very well. The north pole is the one in which the planet, when looked at from above, rotates counter-clockwise. I believe, although I may be wrong (I remember the last time, in 1973 that... well, thats a long story) that Uranuses north pole actually points south of the ecliptic -- unlike most other planets. -- +-----------------------------------+----------------------------------+ | Disclaimer: | David Messer | | I'm always right and I never lie. | | | My company knows this and agrees | UUCP: ...ihnp4!quest!dave | | with everything I say. | FIDO: 14/415 (Sysop) | +-----------------------------------+----------------------------------+
steve@jplgodo.UUCP (Steve Schlaifer x3171 156/224) (02/25/86)
In article <287@drivax.UUCP>, holloway@drivax.UUCP (Bruce Holloway) writes: > In article <860217-235409-1418@Xerox> Murray.pa@XEROX.COM writes: > >How do I tell which end is North and which is South? I assume that the > >"North" pole of Mars is the one that's pointing roughly parallel to the > >North pole of Earth. That doesn't transfer to Uranus very well. > > I think "North" probably means the pole that, when looking down directly > above it, the planet seems to be turning counter-clockwise. Is this right? > According to the IAU, the planetographic north pole of a planet is the one that is above the invariant plane. This is very close to the ecliptic plane. For some planets, Venus for example, this means that when you look down on the north pole, the planet spins clockwise. For others, Earth for example, the spin is counter-clockwise. In this system, Uranus spins clockwise when you are above the north pole. Don't flame me over this choice of convention I don't like it myself. Opinions expressed are my own and not necessarily JPL or NASA. -- ...smeagol\ Steve Schlaifer ......wlbr->!jplgodo!steve Advance Projects Group, Jet Propulsion Labs ....group3/ 4800 Oak Grove Drive, M/S 156/204 Pasadena, California, 91109 +1 818 354 3171
steve@jplgodo.UUCP (Steve Schlaifer x3171 156/224) (02/25/86)
In article <399@utastro.UUCP>, ethan@utastro.UUCP (Ethan Vishniac) writes: > The angular momentum vector of the Earth points toward the North Celestial > Pole. Put it another way, looking down on the Earth from a point above > the North Pole the Earth's rotation is counterclockwise. Therefore, > by convention, the north pole of any planet is that pole from which > the rotation appears counterclockwise. Unfortunately, the IAU (International Astronomical Union) didn't see it that way. Essentially, they decided that the north pole is the one above the invariant plane (ecliptic) regardless of which way the planet spins. It's going to be lots of fun when we get really interested in asteroids and comets :-( -- ...smeagol\ Steve Schlaifer ......wlbr->!jplgodo!steve Advance Projects Group, Jet Propulsion Labs ....group3/ 4800 Oak Grove Drive, M/S 156/204 Pasadena, California, 91109 +1 818 354 3171
bl@hplabsb.UUCP (Bruce T. Lowerre) (02/25/86)
> How do I tell which end is North and which is South? I assume that the > "North" pole of Mars is the one that's pointing roughly parallel to the > North pole of Earth. That doesn't transfer to Uranus very well. Looking down on the North pole of a planet, the rotation is counter-clockwise.
michaelm@3COMVAX.UUCP (02/27/86)
I believe that north and south poles are defined on the basis of the direction of rotation. That pole is the north pole (regardless of the orientation in which it points) which is the axle of rotation in the same direction as Earth. Thus Venus's north pole is defined to point nearly due south with respect to Earth because its rotation takes place in the opposite direction. Cheers! Michael McNeil ..!ucbvax!hplabs!oliveb!3comvax!michaelm *Salvati*. Now what shall we do, Simplicio, with the fixed stars? Do we want to sprinkle them through the immense abyss of the universe, at various distances from any predetermined point, or place them on a spherical surface extending around a center of their own so that each of them will be at the same distance from that center? *Simplicio*. I had rather take a middle course, and assign them an orb described around a definite center and included between two spherical surfaces... Galileo Galilei, 1638, *Dialogues Concerning Two New Sciences*
ethan@utastro.UUCP (Ethan Vishniac) (03/01/86)
In article <578@jplgodo.UUCP>, steve@jplgodo.UUCP (Steve Schlaifer x3171 156/224) writes: > In article <399@utastro.UUCP>, ethan@utastro.UUCP (Ethan Vishniac) writes: > > The angular momentum vector of the Earth points toward the North Celestial > > Pole. Put it another way, looking down on the Earth from a point above > > the North Pole the Earth's rotation is counterclockwise. Therefore, > > by convention, the north pole of any planet is that pole from which > > the rotation appears counterclockwise. > Unfortunately, the IAU (International Astronomical Union) didn't see it that > way. Essentially, they decided that the north pole is the one above the > invariant plane (ecliptic) regardless of which way the planet spins. > After much checking around here I see that I was in error. It seems a bizarre convention to me, but it is the IAU standard. What tripped me up is that the pole of Uranus is habitually described as tipped more than 90 degrees, which is only possible if you worry about the direction of the angular momentum vector. -- "Ma, I've been to another Ethan Vishniac planet!" {charm,ut-sally,ut-ngp,noao}!utastro!ethan ethan@astro.UTEXAS.EDU Department of Astronomy University of Texas