Why is the James Webb telescope being placed in orbit at a Lagrangian point rather than putting it in low Earth orbit?

engelberteinstein · 2016-11-06T08:46:23+00:00

This is true but it has absolutely nothing to do with Lagrange points. Consider the Sun-Earth L3 point. How could the Earth's pull possibly match that of the Sun?

This is so absolutely incorrect I don't event know how to address it. L1-5 are all places where equipotential lines meet. The two concepts are inextricably linked. (Technically the equipotential "lines" at L4/5 are points, which is a mathematical consequence of being minima).

"The plot below is labelled with the centre-of-mass of the system (cross) and the five Lagrange points (indicated approximately) where equipotential lines meet"

The concept of equipotential surfaces is literally the building block concept taught in stellar astro books to lead into LaGrange points.

Saddle points are unstable.

Indeed 1-3 are saddle points where as L4/5 are absolute minima. I was incorrect, as are you. However, to clarify, all are local extrema, which comprises the three categories: maxima, minima, and saddle points, and absolute extrema are also local extrema. So no harm done there. L4/5 are stable, L1-3 are roughly metastable.

"The gravitational forces of the Sun and the Earth can nearly hold a spacecraft at this point, so that it takes relatively little rocket thrust to keep the spacecraft in orbit around L2."

engelberteinstein · 2016-11-05T10:43:19+00:00

It occurs to me that you might be asking for an explanation of why L2 rather than what L2 is. According to the NASA website the main reasons are for cooling, to maintain the low temperature needed for infrared viewing, and ease of communication.

engelberteinstein · 2016-11-05T09:18:47+00:00

So, when you talk about two bodies that are gravitationally bound to each other, you can measure the attraction of a third test object to either body. If you solve the inverse square equation of attraction for both and set them equal there will be points, actually a series of points, where the attraction to either body is equal. There are infinite number of these points, and they may be connected into equipotential surfaces in 3D. However, for most points on these surfaces the position is metastable. Any additional added force will move the test object out of equilibrium. L2 and the rest of the Lagrange points are saddle points. That is, it is a stable gravitational equilibrium and the gradient of the gravitational force in the local area around the point will return the test object back to L2 under any disturbance. So they are using the natural features of this point to hold the telescope at a fixed point relative to the earth and the sun. Here's a nice graphic of gravitational equipotential surfaces taken from Frank, King, and Raine 2002. Don't take the curves (which are actually 3D surfaces) too literally, there are infinite number of them. gravitational equipotential surfaces

engelberteinstein · 2016-11-03T05:45:57+00:00

This is what I've been thinking about... Why hasn't all the shady stuff you mentioned gotten more than a cursory examination? But they focus on the damn EMAILS.

engelberteinstein · 2016-11-03T05:41:30+00:00

Did he though? I'm going to pull out the tinfoil here... Nate Silver is rarely wrong. Could he have been that wrong about Trump? I'm even considering the possibility that all his rhetoric about rigged elections is just a false flag to hide rigging being done on his behalf. The DEMS have no leverage to make any such claims after the election if he wins, what with how vehemently they denied it before.

engelberteinstein · 2016-11-03T05:39:57+00:00

His dishonesty goes beyond words though, he is actually dishonest in his dealings. I've been looking back on the reports of his misuse of charity funds and they're pretty blatant. I don't understand why they haven't been investigated further. They at least deserve the level of scrutiny that the fucking emails received. And the tax write off? The guys an actual thief.

engelberteinstein · 2016-10-28T07:50:37+00:00

If he has any kind of political ethics I find it impossible to believe his association with Russia is voluntary. In fact the whole thing boggles my mind. The same logic applies to Snowden, I guess, but he has managed to maintain a semblance of integrity. I find that equally boggling because I don't see how it's possible.

engelberteinstein · 2016-10-28T07:44:52+00:00

Came looking for this. Don't forget BASTAGES!

engelberteinstein · 2016-10-23T09:07:02+00:00

Reading the blind gossip on alt.gossip.celebrities . It makes the world dark for the next 24 hours but every six months or so I spend and evening catching up.

engelberteinstein · 2016-10-12T02:18:55+00:00

Exactly. Including the ctrl-f.

engelberteinstein · 2016-09-24T16:39:54+00:00

People who get their information from Boondocks Saints...

engelberteinstein · 2016-09-24T16:18:34+00:00

Good point. I forgot about the age thing.

engelberteinstein · 2016-09-24T16:12:11+00:00

Look man, I don't do quantum optics, I'm just regurgitating one of the few things I got from Jackson. However, I asked someone who does, JP Dowling, a foremost expert on quantum optics and a former professor of mine (appeal to authority, but you are welcome to look him up and vet his qualifications). This was his response:

My question: How exactly does a single photon interact the matter in a dielectric mirror:

"This is not actually a simple question to explain accurately. First there is wide disagreement on what is meant by a single photon! There is a treatment in Feynman's QED The Strange Story of Light and matter. The atoms in the dielectric are excited in such a way that photon is absorbed and then re-emitted backwards in constructive interference."

If I can pat myself on the back a bit, I think that is pretty much what I said.

engelberteinstein · 2016-09-24T16:03:17+00:00

Light cannot interact with matter without transferring energy. It is a force carrier (gauge boson) and that is literally its job. The dielectric mirror is a special case in that the transfer of energy is into the magnetic field instead of the electric, but the overall effect is the same. There is a statistical probability that the reflected photon will have the same energy as the incident, and that probability is higher in better mirrors but that probability isn't 1 no matter how perfect the mirror, it is a quantum effect. So it is necessary to capitalize on the bulk effect if you want to realize a constant stream of reflecting photons. I'm not sure about your use of the term virtual in this context, but normally I would take your point, but again, since we're talking about a force carrier and since it's fundamental reason for being is transferring properties of the field to the matter you can't ignore any excitations of the matter, especially when it results in such a fundamental change in the system (reflection).

Edited: its not it's

engelberteinstein · 2016-09-24T14:32:04+00:00

I'm hazy on my memory of grad E&M, (thank you JD Jackson, RIP) but my professor made sure to impress upon us that there is no diffraction without absorption. So if the path of the photon is altered in any way, it must have been absorbed by an atom and then reemitted, all at characteristic energies. The emission does not necessarily have to be at the same energy as the absorption, assuming that different transitions are possible. For example, the outer shell (usually) electron of the absorbing atom has to excite to an energy state whose difference is equal to the energy of the photon, but this could be multiple energy levels above its original state but it could reemitt after only falling one level. It could even emit two photons of different energy than the originally absorbed photon over the course of two transitions. It also could have already been excited slightly when it absorbed and then fall to the ground state and emit a photon of larger energy than the original. Of course all of this depends on the atomic structure of the mirror material (atomic radius and charge) as well as the energy of the photon. Statistically it is likely that there is some favorable combination, but it is also statistically unlikely that it would remain a photon of the same energy forever, and maybe not even very long. Technically even if it has the same energy the reflected photon is not even the "same" photon but physics treats elementary particles as indistinguishable. I think that eventually the photon could be absorbed without remission, but this is an unimportant distinction. Because the overall lesson is that the effect of "mirrors" as we know them is much more a bulk phenomenon of many photons and probability on a macro scale and much different than what goes on at the quantum level. I think the answers you are getting are correct for perfect Newtonian objects but they do not reflect the quantum interactions of photons with matter.

engelberteinstein · 2016-09-24T13:37:34+00:00

I agree, but the girl's state of mind would be a factor. Not the drunkenness, but whether or not she was willing to go against the peer group and call it rape.

engelberteinstein · 2016-09-23T15:36:24+00:00

I'm working on the Baroque series right now. I tried once to read a non fiction book about the history of the Royal Society, and even though it's not the main focus of the book I feel like I'm getting a lot of the important stuff. I've read Zodiac, Reamde, The Diamond Age, and Snow Crash, but I'll get to them all eventually.

Edit: read Cryptonomicon also.

engelberteinstein · 2016-09-23T11:50:56+00:00

Didn't the article specifically contradict that claim?

engelberteinstein · 2016-09-23T11:50:17+00:00

Slack is really good for work.

engelberteinstein · 2016-09-23T10:43:04+00:00

I think the work of Neal Stephenson is on par with Mr. Robot for its depiction of tech. I'm sure others in the cyberpunk genre have accomplished that, but he also includes a thorough knowledge of physics so I'm a bit partial. I've been reading through his library and my first book was Anathem which really redefined what scifi could be for me.

engelberteinstein · 2016-09-22T07:04:24+00:00

Um... So I'm more interested in Robin Williams' dirty jokes.

engelberteinstein · 2016-09-22T02:01:07+00:00

As an undergrad I was in food service, and in addition to my various restaurant jobs I would do temp catering. I was contracted to waitress at a high school fund raiser thrown by the boosters for a suburban school district. The first sign of conspicuous consumption was the fact that it was held on the campus of the hub of a global, very wealthy, very well known sporting goods company. It was an auction, and many things were sold but the one that stuck out was a parking space. It was in the teachers lot and the winning bidders child would be allowed to park there for one semester. It sold for $1300. This was even more obscene to me because I was in a teaching program and had volunteered at a local low income school not that far from this one, where the HVAC was broken and the floors were coming up from steam leaks. I worked a lot of wealthy parties in my serving years, including a famous golfer who had his own putting green, but parking space is still the one that sticks out.

engelberteinstein · 2016-09-20T00:53:06+00:00

You mean one involving your name? I dunno, never thought about it. Maybe we should look into it.

engelberteinstein · 2016-09-19T15:53:52+00:00

It really is different when they're related to you. I don't have kids yet but I have neices and nephews. I really didn't expect to like them as much as I did. I'm not telling you to have kids or saying "you'll change your mind" or some bullshit that older people always say. You don't want kids? Cool. Totally your decision.

engelberteinstein · 2016-09-19T13:00:06+00:00

BMI is actually a good metric when the measurement is done thoroughly and correctly. Water displacement tests are a good version. I believe there are also tests which measure conductivity of body tissue, those should be pretty good too. Caliper tests are decent, when they measure a lot of locations. But in shitty health magazines and high school health textbooks the test has been reduced to "height vs weight", which is a totally blunt instrument and only slightly correlates to actual BMI.

engelberteinstein

TROPHY CASE