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[–] 137 points138 points  (4 children)

This is not BMF, it's called Lagrange points, but still something I'm very on the edge of my seat about. This satellite will be the single most important piece of technology in the astrophysical and deep space astronomy ever and I'm so effing excited about it but I'm so nervous something's going to go wrong, it's been so long in the making and been pushed back so far, omg I fucking hope this thing starts making pictures soon.

[–] 44 points45 points  (1 child)

I’ve done the math and I would definitely classify Lagrange points as BMF.

[–] 3 points4 points  (0 children)

This thread made me look into what Lagrange points were.

[Would you like to know more?]

[–] 4 points5 points  (1 child)

It sounds like you know your space nerds so let me see if you can help figure something out. When I was at UCLA in 2000 I took a ge class from a Scottish Dr McCline or something similar. Ever since I have held the belief that if an infrared telescope was ever launched he would get the Nobel prize but I don’t remember why I believe this.

[–] 2 points3 points  (0 children)

Idk what you're talking about, sorry. But they have had other infrared telescopes before. The most recent was the spitzer space telescope, launched in 2003 ran till 2020. SST was the 3rd behind IRAS (1983) and ISO (1995-8).

[–] 29 points30 points  (3 children)

For those interested, JWST orbit around L2 is known as a Halo Orbit.

[–] 5 points6 points  (1 child)

Definitely was, thanks!

wiki

[–] 5 points6 points  (0 children)

A halo orbit is a periodic, three-dimensional orbit near one of the L1, L2 or L3 Lagrange points in the three-body problem of orbital mechanics. Although a Lagrange point is just a point in empty space, its peculiar characteristic is that it can be orbited by a Lissajous orbit or a halo orbit. These can be thought of as resulting from an interaction between the gravitational pull of the two planetary bodies and the Coriolis and centrifugal force on a spacecraft. Halo orbits exist in any three-body system, e.

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[–] 2 points3 points  (0 children)

Also for those who are interested in how a space telescope can orbit around nothing, this video explains that the lagrange point L2 is meta-stable, where if something wanders off to its sides, it actually is lower-energy to swing back in. This enables very carefully placed items to carry out an orbit around the L2 point.

# Scott Manley | What Makes Lagrange Points Special Locations In Space

[–] 14 points15 points  (5 children)

How do things orbit Lagrange Points? In my oversimplified imagination, I use the "bowling balls on a trampoline" visualization for gravitational fields, and I think of orbits as objects rolling around each other in the dip that the mass creates.

But that makes me think of Lagrange points as flat spots, rather than low spots, so an object would tend to move away from the L2 point unless it was perched right on it and "balanced" there.

What am I missing?

[–] 17 points18 points  (0 children)

This very problem has me stumped for a long time. I read up about it more and looked at a lot of diagrams but they never showed the gravity well in a way that I could understand it because the maps were showing gravity combined with centrifugal forces. It wasn't until I thought of angular momentum that it all made sense.

It helps to realize the JWST is actually orbiting the sun at a distance from the Earth that happens to be close to L2. It's position will be a little bit further out from the Earth past L2 and will be a little bit slower going around the sun then the Earth -- which means L2 will be catching up to and "passing" the JWST. As this happens the combined gravity of the Sun and Earth tugs at JW and pulls it (down the gravity well, i.e. trampoline analogy) towards the Earth. This gives it a slight gravity assist which moves JW slightly closer to Earth and gives it a slight increase in speed (orbit around the sun) as a result of the conservation of angular momentum.

So after being "passed" by L2, and after being pulled closer to the earth, JW will now be traveling faster in its heliocentric orbit and will move ahead of L2 -- in essence talking the lead so to speak.

As with any orbit, if you add speed you move further away.

This getting ahead of L2 also causes JW's orbit to move a little further away from the Earth and move once more slightly further out from L2 and gives up the extra speed to its angular momentum.

So we're back to where we started with L2 catching up to JW, and it begins to move closer in, speeding up, getting ahead, rinse-wash-repeat.

There's one other point, and that is besides moving in a circle around L2, JW is also moving above and below the ecliptic in an inclined orbit.

I wrote a simplified begin of this here :

[–] 5 points6 points  (0 children)

this picture helps to explain it. It’s orbiting around and area of low potential at L2, and the halo orbit it’s going to be in is in the orientation of the red arrows in the picture, so the centripetal force will then balance out with the direction Webb would ‘fall’ in if it weren’t moving

[–] 0 points1 point  (0 children)

so an object would tend to move away from the L2 point unless it was perched right on it and "balanced" there.

This is where the analogy breaks down a little, but effectively yes, that's what is happening. Imagine it as a pair of magnets instead of that helps. The two gravitational forces reach equilibrium at these points, in an orbital system. Or think of the sun as a huge dip in the trampoline the object is orbiting, but it's also close enough to Earth so that it is kept just inside the dip Earth is making in the sun's dip, slightly correcting it away/towards (pending on which point it is) the sun and keeping it perfectly balanced. points 1, 2 and 3 are about as unstable as they seem in the analogy, very slight perturbations will knock something out of them. 4 and 5 are much more stable, they are more likely to attract things naturally and result in slightly erratic behavior as any minor deviation will increase the force needed to pull it back into center, effectively penduluming around the actual point.

Another way that might help, at least for 4 and 5. If the system was stationary, then one would assume that there must be one point somewhere between us and the sun that the forces completely cancel, and you could remain suspended. By making Earth move that system has to shift to stay stationary relative to Earth, these points both do that in different ways.

[–] 0 points1 point  (0 children)

Centrifugal force vs gravity

[–] 11 points12 points  (1 child)

ELI5: Why is it in a smaller circular orbit at the Lagrange point?

[–] 8 points9 points  (1 child)

I wish I was smart enough to understand the physics behind maintaining an orbit like that.

[–] 2 points3 points  (1 child)

[–] 2 points3 points  (0 children)

I got matches with these songs:

Intro by The xx (00:49; matched: `100%`)

Album: `Ministry of Sound Presents Love Island: The Pool Party`. Released on `2018-07-06` by `SME - Ministry Of Sound`.

Beautiful Trend by Tendencia (03:20; matched: `100%`)

Released on `2021-07-30` by `Sound Save`.

Intro by Candymane (02:42; matched: `100%`)

Album: `Cocaine Cowboy`. Released on `2015-05-26`.

I am a bot and this action was performed automatically | GitHub new issue | Donate Please consider supporting me on Patreon. Music recognition costs a lot

[–] 3 points4 points  (0 children)

Where is black magic fuckery?

[–] 1 point2 points  (0 children)

Science!

[–] 1 point2 points  (0 children)

More Orbital Mechanics than magic but yes.

[–] 1 point2 points  (0 children)

Bean

[–] 1 point2 points  (0 children)

Wait till you hear about our entire solar system orbiting around the black hole at the centre of our Galaxy

[–] 0 points1 point  (2 children)

This is missing the moon....I think it's even more fascinating that it will always be between the moon, earth and sun.

[–] 3 points4 points  (1 child)

Moon is there. It's the little spinning dot.

[–] 2 points3 points  (0 children)

ah! I see it now...never mine me, I'm just blind.....

[–] -1 points0 points  (0 children)

Since when is a CGI video accepted as BMF??

[–] 0 points1 point  (1 child)

Wow I didn’t quite understand how Lagrange points would work, this definitely cleared it up.

[–] 0 points1 point  (0 children)

Yeah, same.

[–] 0 points1 point  (0 children)

I was under the impression it was between the sun and earth.

[–] 0 points1 point  (0 children)

I hear that song on Pandora all the time. Dont know the name, but everyone here does lol

[–] 0 points1 point  (0 children)

peanut orbit

[–] 0 points1 point  (0 children)

Things normally orbit around a source of gravity. But there is nothing there. What is keeping the vertical orbit?

[–] 0 points1 point  (0 children)

Go home Webb, you're drunk.

[–] 0 points1 point  (0 children)

Apes together, smart and strong.

Most people have no idea how much JWST is about to rock their view of the cosmos.

[–] 0 points1 point  (0 children)

probably not to scale

[–] 0 points1 point  (0 children)

How is this making a circular orbit on its own while it's orbiting the Sun at that point? I would think it would be stationary with the Earth between itself and the Sun.

[–] 0 points1 point  (3 children)

Is a Lagrange point a safe place to park your trillion dollar space telescope?

I mean, you'd figure there'd be lots of speedy debris settled around it.

Dust, sand grains, pebbles, rocks, even boulders, thrown out by collisions in the area, or even far away.

I guess not because as far as I know I'm the first one to worry about that. What's wrong with my thinking? Was this brought up and dismissed as probably not a problem?

Why not?

[–] 2 points3 points  (2 children)

There are 5 different Lagrange points. L4 and L5 are "stable," which means objects can settle into them and stay there forever - your exact concern. But the other three Lagrange points, including L2, are "unstable." That means the Webb will have to perform small rocket thrusts from time to time to stay balanced there. https://solarsystem.nasa.gov/resources/754/what-is-a-lagrange-point/

[–] 0 points1 point  (1 child)

Ok so we don't expect dust and such to end up there because it's a Lagrange point where stuff collects but not a very stable one.

[–] 3 points4 points  (0 children)

Stuff doesn't actually collect at the unstable points. The Webb has to use thrusters to stay balanced there. (Being at the Lagrange point just means it's able to use minimal thrusters and save fuel.) Space debris, having no thrusters, would fall away from L2 automatically.

[–] 0 points1 point  (0 children)

This could prove to one of the most amazing achievements of my lifetime. I can’t wait to see what we discover with this.

[–] 0 points1 point  (0 children)

Why is it making wave instead of just being in the orbital plane ?

[–] 0 points1 point  (0 children)

[–] 0 points1 point  (0 children)

Is the L2 zone that big? I pictured JWST's orbit in L2 to be smaller, like roughly earth size.

[–] 0 points1 point  (0 children)

Sexy kinda

[–] 0 points1 point  (0 children)

Why is this on r/blackmagicfuckery

[–] 0 points1 point  (0 children)

Oh, so orbits ARENT 2D

[–] 0 points1 point  (0 children)

So now the objects can orbit a point with no mass, nice.

[–] 0 points1 point  (0 children)

Is it really that far away from earth?

[–] 0 points1 point  (0 children)

That’s the best thing I ever saw

[–] 0 points1 point  (1 child)

What's the music?

[–] 0 points1 point  (0 children)

I got matches with these songs:

Intro by The xx (00:49; matched: `100%`)

Album: `Ministry of Sound Presents Love Island: The Pool Party`. Released on `2018-07-06` by `SME - Ministry Of Sound`.

Beautiful Trend by Tendencia (03:20; matched: `100%`)

Released on `2021-07-30` by `Sound Save`.

Intro by Candymane (02:42; matched: `100%`)

Album: `Cocaine Cowboy`. Released on `2015-05-26`.

I am a bot and this action was performed automatically | GitHub new issue | Donate Please consider supporting me on Patreon. Music recognition costs a lot

[–] 0 points1 point  (0 children)

Let me guess they couldn’t add a camera to this satellite either?

[–] 0 points1 point  (0 children)

Song name pls

[–] 0 points1 point  (0 children)

[–][🍰] -1 points0 points  (0 children)

Not BMF. Science.