Jestful Statement - 09 - HD
Added 2021-12-14 06:36:00 +0000 UTCActual EGSNP in not-actual SPACE -
Commentary
I've heard that some people are confused by other people of different genders. I am aware that this is a farfetched concept, but I've decided to partly explore it for the sake of hijinks in a fictional story, which is something I believe has never been attempted before.
TO THE MOOOOOON!
The group assignment is based on an actual group assignment I had in high school. I don't remember all the specifics, but I do remember the idea being somewhere other than Earth, and one of the items being compass (I'm not 100% certain the actual scenario was on the moon).
I asked myself Grace's question, thought of the logic in panel two, and then countered that logic with "what if that's intentional, and the compass is a bad idea?" I vaguely remember not being able to focus on much else. My mental compass was stuck pointing at the hypothetical compass.
My understanding now is that a compass on the moon probably wouldn't point north, but might react in some way on the moon. I suppose that could potentially help with navigation in some way, but it wouldn't be as straightforward as going by cardinal directions.
Comments
If you're on Nearside, it might be better to navigate by the position of the Earth in the sky rather than the Sun? Because while the Sun moves slowly, the Earth doesn't move at all (or at least, negligibly).
Adama
2021-12-23 03:34:38 +0000 UTCOh, that's a very interesting device. It would probably take longer to align to the poles on the Moon, and be easier to disrupt, due to the much slower rotational rate and thus lower forcing torque, but it should work if you're careful. I could see it being quite useful on faster-spinning objects like Mars or maybe the Jovian satellites. Possibly Titan would be a good use case, even with its 15-day orbital period/day, since it doesn't have (much of?) an intrinsic magnetic field (though Saturn's may be usable), and also doesn't have any sky visibility from the surface. I wonder what the Dragonfly octocopter mission to Titan is using for navigation... As for the Moon, one of the "simpler" methods of determining your location, since the stars are always visible, is a star tracker (a satellite navigation device that tells you your orientation relative to the celestial sphere), combined with an accelerometer to determine which way is down and a clock and model of the Moon's orientation in space. With that, you can determine your position on the surface to the angular accuracy of the star tracker. From a quick Google search, it looks like you could probably get better than 100m positional accuracy on the lunar surface (and you'll get your heading as a free bonus). If you just want your heading, and already know roughly where you are, a sun tracker will actually work well, since the sun moves so slowly- the Apollo astronauts used a (carefully calibrated) little stick that cast a shadow to set the inertial navigation device on the lunar rover before each jaunt. (By the way, the "3D-ness" of a magnetometer doesn't really help with navigation, what it will do is tell you the exact orientation and strength of the magnetic field lines, which will help to determine what sort of subsurface magnetized feature is creating that field: Is it one big blob? Several adjacent blobs? How deep is it? How does this agree with theories about what it is and how old it is? For example, if it's a single hundred-km-long feature 3 km down, that's probably a blob of intrusive magma that cooled and preserved the Moon's original magnetic field from before the core (mostly) froze, but if it's a whole bunch of little near-surface features, that might indicate a more recent origin from impact(s). The biggest problem with trying to use a magnetic compass to navigate on the Moon is that even in the few places that do have magnetism, we don't know which way(s) it's pointing at ground level- all we have so far is measurements from orbit, and there could be a lot of ground-level complexity that isn't detectable from 50 km up. Far easier to use stars. Or maybe gyrocompasses?)
Rob W
2021-12-15 05:44:42 +0000 UTCI would also note that, although compasses are normally magnetic, there's nothing saying that this is a magnetic compass. It could be a gyroscopic compass? Also, I was today years old when I learned about gyrocompasses, which are not (as I had assumed) just relying on a gyroscope to keep pointing in the same direction, but instead use a gyroscope to sense the rotational axis of the planet -- or, presumably, moon -- that they are sitting on. More at https://en.wikipedia.org/wiki/Gyrocompass. The moon of course rotates rather more slowly than the earth does, but I think a gyrocompass should still be workable.
Brooks Moses
2021-12-15 00:36:40 +0000 UTCWow, I did not expect to get an explanation from an actual NASA scientist. Man, mere decades ago this would've been impossible. Thanks for explaining and thanks to everyone else for responding, too. Now I want the guys in the comic to clarify that that compass is actually a 3D one. XD I mean, after pissing off Grace by explaining to her that cliché about girls being naturally difficult to understand they could go back to her original question.
Applestone
2021-12-14 18:16:49 +0000 UTCNASA scientist here: Congratulations, you've wandered into an area that I'm fairly familiar with! Your intuition was good that a compass might not work for navigation on other planets- Earth and Mercury are the only rocky bodies in the solar system with intrinsic magnetic fields, and Mercury's is very weak. On the Moon in particular, there's no global magnetic field, but there are a few patches of (very weak) magnetic field scattered around, usually associated with strange bright "swirl" patterns (look up "Reiner Gamma" for the best example). These small fields are probably strangely enough structured that even if you were inside one, a compass wouldn't help you navigate- it probably would be sort of like using a compass on top of the north magnetic pole. Also, again, they're very weak, and a normal compass might not even respond to them. There's actually a mission under development now (Lunar Vertex) that will go to one of those magnetic anomalies and use, among other instruments, a sensitive magnetometer (3D compass, basically) to try to figure out exactly what's going on, and what the connection is with the bright patterns. So, there is a use for a compass, but it's not for navigation.
Rob W
2021-12-14 17:43:02 +0000 UTCSo it can still be used to detect magnetic rocks, i.e. iron (or other magnetic) ores. And if you're prospecting that might be important. But whether it is or not, what are the other fourteen supplies, and what are you bringing that's not part of the group of fifteen?
Foradain
2021-12-14 15:25:33 +0000 UTCMen are from Mars, women are from Uryuom?
Narzain
2021-12-14 14:31:54 +0000 UTCExactly: the compass wouldn't "work" because the moon has no magnetosphere for it to pick up However, I"d like to point out that the Earth *does* produce an electromagnetic field, and a compass on the moon would probably react to it. So, if anything, I guess a compass on the moon would point to... Earth. Which is technically useless, but kinda awesome if you think about it. Edit: after doing some checking, I'm afraid my expectations have been shot down. It seems the moon is far enough from Earth that it would make its magnetic field pretty much unsignificant. Basically, a compass would likely point to the nearest magnetic rock, the innards of your spaceship or whatever the local magnetic anomaly could be. Needless to say, I'm quite disapointed about this.
Rémy
2021-12-14 09:55:51 +0000 UTCThere is some magnetism on the moon, but there is no dipole with north and south. I guess it is comparable to the deviations in the earth magnetic field. [speculation] I think it is formed during crater impacts.
Joachim
2021-12-14 08:54:17 +0000 UTCThe moon is geologically dead and doesn't have its own magnetic field. A compass wouldn't work.
Chordat
2021-12-14 08:43:32 +0000 UTCRegarding the compass: Well, if they already are on the moon and have to pick equipment for exploring it, then they can simply try whether or not the compass works.
Applestone
2021-12-14 08:26:51 +0000 UTCWahahahaha I did not see that one coming! XD
Applestone
2021-12-14 08:25:08 +0000 UTC
