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There's a relatively new video on YouTube by Launch Pad Astronomy named "How James Webb Orbits 'Nothing'" [0] which left me baffled on how they are capable of o

There's a relatively new video on YouTube by Launch Pad Astronomy named "How James Webb Orbits 'Nothing'" [0] which left me baffled on how they are capable of orbiting "around" L2, which I had been thinking about for some weeks now and never could find a solution to it. I think Webb is not the first one to do this, but the video makes it clear how crazy the planning of the orbit insertion and staying in orbit must be. I hope that the NASA could release some details on this. [0] https://www.youtube.com/watch?v=ybn8-_QV8Tg https://www.youtube.com/watch?v=ybn8-_QV8Tg

sandworm101 5y ago
Some would say it really isnt an orbit. Orbit presumes a single attractive force (gravity or magnetic) from one body while another moving body is held away by momentum. The circular path around an L point is more a confluance of attractive forces from two bodies. The object is not held up by momentum rather than by balanced pulls of multiple attractive forces. If there is no minimum required velocity to maintain altitude, it isnt really an orbit imho.
- mannykannot 5y ago
  From a physics point of view, an orbit around a celestial body is just a special case of a more general phenomenon. The explanation is the same, only the numbers giving the spatial distribution of the gravitational potential within the gravity well are different. > If there is no minimum required velocity to maintain altitude, it isnt really an orbit imho. If you put, into a gravity well, a body that is initially stationary with respect to the location of the well's minimum potential, but offset from it, it will begin to move on an orbit, under the influence of that gravitational potential. The JWST orbit is more complicated, because L2 is a potential saddle, not a well, and it is affected by the moon's gravity, but I think one needs to be aware of the points I made above before one can begin to deal with those complications.
  - sandworm101 5y ago
    That goes down the road of saying that every circular path is an orbit. I'm reminded of the concept that the sun "orbits" around in the milky way. I don't really consider that an orbit either because the dynamics are totally different. I try to use "orbit" in relation to objects moving around a larger mass and/or a barycenter, which is conceptually a location of average mass. A third tiny object is rather in an orbit around one of the the bodies but that which is constrained by the gravity of the second.
    - mannykannot 5y ago
      > That goes down the road of saying that every circular path is an orbit. That is a route I explicitly did not take, because arguments from dictionary definitions, if the issue is not specifically lexical, are usually just pedantic ways of avoiding the issue. >...the dynamics are totally different. It was a very important scientific discovery that they are, in fact, very similar, explicable from a small set of universal premises. This is a pattern that is observed widely throughout the sciences. A universe in which just the things you have mentioned were totally (or just largely) different would be a universe with entirely different physics than ours! >...and/or a barycenter... You seem to be inconsistent here, as, just before, you rejected the notion that the sun orbits around the milky way. > I don't really consider that... I try to use "orbit" in relation to... Claiming that it is wrong to use 'orbit' for the motion of the JWST around Earth's L2 on the grounds that this usage is not in your personal dictionary is not much of an argument - it is very similar to, but even weaker than, the sort of argument that you wrongly insinuated I was making! (And you cannot say I am doing the same, as I am defending the common usage among those who work with this issue - most specifically, those who are controlling the JWST.) Even the metastability of the JWST orbit is not much of a basis for your position, given that the orbits of the planets in the solar system, and of satellites around the earth, are also ultimately unstable.
    - spookthesunset 5y ago
      On the “sun orbits the galaxy”… I’ve read that the galaxy isn’t bound together by some massive black hole but instead by dark matter. The black hole in the center doesn’t have nearly enough mass for things like the sun to orbit it. So what is the sun and all its neighbors actually orbiting around?

sandworm101 5y ago

Some would say it really isnt an orbit. Orbit presumes a single attractive force (gravity or magnetic) from one body while another moving body is held away by momentum. The circular path around an L point is more a confluance of attractive forces from two bodies. The object is not held up by momentum rather than by balanced pulls of multiple attractive forces. If there is no minimum required velocity to maintain altitude, it isnt really an orbit imho.

mannykannot 5y ago
From a physics point of view, an orbit around a celestial body is just a special case of a more general phenomenon. The explanation is the same, only the numbers giving the spatial distribution of the gravitational potential within the gravity well are different. > If there is no minimum required velocity to maintain altitude, it isnt really an orbit imho. If you put, into a gravity well, a body that is initially stationary with respect to the location of the well's minimum potential, but offset from it, it will begin to move on an orbit, under the influence of that gravitational potential. The JWST orbit is more complicated, because L2 is a potential saddle, not a well, and it is affected by the moon's gravity, but I think one needs to be aware of the points I made above before one can begin to deal with those complications.
- sandworm101 5y ago
  That goes down the road of saying that every circular path is an orbit. I'm reminded of the concept that the sun "orbits" around in the milky way. I don't really consider that an orbit either because the dynamics are totally different. I try to use "orbit" in relation to objects moving around a larger mass and/or a barycenter, which is conceptually a location of average mass. A third tiny object is rather in an orbit around one of the the bodies but that which is constrained by the gravity of the second.
  - mannykannot 5y ago
    > That goes down the road of saying that every circular path is an orbit. That is a route I explicitly did not take, because arguments from dictionary definitions, if the issue is not specifically lexical, are usually just pedantic ways of avoiding the issue. >...the dynamics are totally different. It was a very important scientific discovery that they are, in fact, very similar, explicable from a small set of universal premises. This is a pattern that is observed widely throughout the sciences. A universe in which just the things you have mentioned were totally (or just largely) different would be a universe with entirely different physics than ours! >...and/or a barycenter... You seem to be inconsistent here, as, just before, you rejected the notion that the sun orbits around the milky way. > I don't really consider that... I try to use "orbit" in relation to... Claiming that it is wrong to use 'orbit' for the motion of the JWST around Earth's L2 on the grounds that this usage is not in your personal dictionary is not much of an argument - it is very similar to, but even weaker than, the sort of argument that you wrongly insinuated I was making! (And you cannot say I am doing the same, as I am defending the common usage among those who work with this issue - most specifically, those who are controlling the JWST.) Even the metastability of the JWST orbit is not much of a basis for your position, given that the orbits of the planets in the solar system, and of satellites around the earth, are also ultimately unstable.
  - spookthesunset 5y ago
    On the “sun orbits the galaxy”… I’ve read that the galaxy isn’t bound together by some massive black hole but instead by dark matter. The black hole in the center doesn’t have nearly enough mass for things like the sun to orbit it. So what is the sun and all its neighbors actually orbiting around?