Timeline for Does it make any scientific sense that a comet coming to crush Earth would appear "sideways" from a telescope and on the sky (from Earth)?
Current License: CC BY-SA 4.0
16 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Nov 4, 2020 at 20:44 | comment | added | Wayne Conrad | @Tim At least on Earth, the angle stays the same for two vehicles on a collision course even if their speeds are different. For example, if a pilot sees an aircraft stay in the same spot on the windscreen, that gets the pilot's immediate attention: flyingmag.com/technique/tip-week/beware-stationary-objects . But neither the Earth nor the comet are moving in a straight line; I don't know if that changes things. | |
| Nov 4, 2020 at 7:41 | comment | added | Tim | @nick012000 only assuming they are traveling at the same speed. If one goes faster, the angle varies. | |
| Nov 4, 2020 at 7:39 | comment | added | Tim | @bdsl the Earth | |
| Nov 3, 2020 at 22:36 | comment | added | nick012000 | @Acccumulation Nah, it’d still apply right up until the moment of impact. Consider two cars moving towards a 90 degree intersection where they’ll collide. They’ll maintain a constant angle between them right up until impact. | |
| Nov 3, 2020 at 1:38 | comment | added | Acccumulation | That applies if the comet is several months out, but not if it's only a few days away. | |
| Nov 2, 2020 at 23:30 | comment | added | bdsl | @DarthFennec But direction of motion relative to what reference? | |
| Nov 2, 2020 at 19:59 | comment | added | DarthFennec | @NuclearHoagie I read the question in two parts. One, making the incorrect assumption that the tail is "behind" the comet. Two, making the incorrect assumption that the trajectory of a collision course would be directly toward an observer. Showing that either assumption is false is enough to answer the question, but I would argue that you need both for a complete answer. So, sure, the question is technically asking about the tail, so focusing on the tail is valid, but I think it ignores the other (more implicit) half of the question. | |
| Nov 2, 2020 at 19:49 | comment | added | DarthFennec | @bdsl By "directly behind" I of course mean "opposite to the direction of motion". I thought that was obvious from context but sure, I could have been more clear. | |
| Nov 2, 2020 at 19:25 | comment | added | Nuclear Hoagie | @DarthFennec ... the rephrased question is not at all equivalent to the original one. You're correct that a comet on a collision course with earth will probably not have a trajectory pointed directly at earth. But that gives absolutely no information about the trajectory of the tail. A comet with a trajectory nearly orthogonal to the direction of earth could still have a tail pointed directly at the planet. Or, it could have a tail pointed orthogonally to the direction of earth. | |
| Nov 2, 2020 at 19:04 | comment | added | Nuclear Hoagie | @DarthFennec But there's no point in discussing the trajectory, as it doesn't affect the tail in any way. Whether or not the trajectory is pointed directly toward the earth, or toward where the earth will be, makes no difference. Even if the trajectory points directly at the earth, you could still see a side-on tail, like if the comet was in the earth's orbit but going the opposite direction. Or, you could have a trajectory pointing directly at the earth with a head-on tail, like if the comet comes from far outside the earth's orbit. The trajectory is irrelevant to the direction of the tail. | |
| Nov 2, 2020 at 18:29 | comment | added | bdsl | The concept of "directly behind" doesn't really make sense in space. All motion is relative. | |
| Nov 2, 2020 at 18:27 | comment | added | DarthFennec | @NuclearHoagie I think the point though is that even if the tail points directly behind the comet, that doesn't necessarily mean you won't see it sideways. The question could be construed as "if a comet was on a collision course with Earth, wouldn't its trajectory be directly toward an observer on Earth?" and I would say the answer to that is no. | |
| Nov 2, 2020 at 17:48 | comment | added | Nuclear Hoagie | This doesn't really have anything to do with it - the trajectory of a comet makes no difference whatsoever in where the tail points. Yes, you can see a comet tail side-on from the earth, but whether the comet is heading toward earth, or toward where the earth will, or in any other direction won't change a thing about where the tail points. How a comet's tail looks only depends on where it is, not where it's going. | |
| Nov 2, 2020 at 10:51 | comment | added | Oscar Bravo | @uhoh I'd go a bit further... It's half the answer. The other half is in the answer by Ingolfis. | |
| Nov 2, 2020 at 5:14 | comment | added | uhoh | This is not really the right or at least the complete answer yet. You should begin with "The only wind the comet experiences comes from the Sun" and then describe why comets have two tails sometimes. But it is good that you've pointed out that since both objects primarily orbit the Sun their collision trajectories will not have them moving straight at each other. | |
| Nov 2, 2020 at 4:14 | history | answered | Pitto | CC BY-SA 4.0 |