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OK, lots of questions! 1. I'm sure in the latest Sky at Night they discussed the Sun being "at least a 3rd generation star", ie its composition is such that it is not 1st or 2nd generation. But I'm sure they also said that this would have been contributed to by many novae, which I took to mean...

Thanks, that was a very helpful post (ditto to 256bits and Drakkith), especially the bit about angular momentum. I would just observe what I said in my reply to Drakkith about most systems consisting of 2 or more stars.

Again, without wishing to theorise, I would observe that most systems consist of 2 or more stars. No, I am quite happy to accept that stars form from the gravitational collapse of a gas cloud. I guess what I am questioning is the theorized formation of planets by accretion as part of that...

a. So the Sun and the planets all formed from the same gas cloud, but the [core of] the Sun is not the same as the [core of] the planets? b. My understanding is that Theia did not survive the collision with the proto-Earth, but the orbiting ejecta from the collision subsequently accreted to form...

OK, so I guess I was trying to establish whether or not there was any reason why the planets did not form as a consequence of a body colliding with the Sun. The only answer seems to be that the current accepted theory for planetary formation is one of accretion, which doesn't really answer my...

Thanks. The first line of that caught my eye: "The various planets are thought to have formed from the solar nebula, the disc-shaped cloud of gas and dust left over from the Sun's formation." So we don't actually know the process of planetary formation. But moreover, this hypothesis is...

Ah, something else for my to-do list 8-)

OK, but we haven't be able to observe what the subsequent result is - that will take millions of years. I guess what I'm asking is do we know whether or not planetary systems are formed as the consequence of the collision of two stars? EDIT: Another way of looking at what I'm asking is how...

OK, well as I understand it a star is formed when a gas cloud collapses. Have we observed what happens when two stars collide? OK, I still don't really understand what that means 8-) But on a related note, the universe contains a fixed amount of matter. So does the universe therefore have a...

OK, well I guess I'm just trying to understand how we know that the solar system did not form in the same way that it is theorized that the Earth-Moon system was formed. OK, well I don't understand what that means!

Really? It's that closed-minded? OK, I'll add that to my to-do list 8-) One quick question (getting completely off-topic now): if there had been just a single Big Bang then surely all of the matter in the universe would essentially describe the surface of a sphere, no?

No, of course not. But the universe as we know it could be the product of more than one Big Bang. You seem really quite defensive. I'm just a curious amateur asking questions.

Well surely that all comes down to how all the matter was formed in the first place - it would be good evidence that there wasn't a single Big Bang, I guess. But that's going off at a tangent, somewhat.

Surely the inhomogenious spread of the gas is irrelevant since the cloud of gas will have a single centre of gravity, and therefore all the matter will move to that point (rather than clumping together first) regardless of its spread? EDIT: Or are you saying that the gas cloud doesn't collapse...

Sure, I appreciate that. My point is that we have not actually observed the formation of any particular solar system so we can only theorise as to how they form. I guess the biggest problem I have is that if a cold cloud of gas collapses under its own gravity then it will ipso facto collapse...

Then by a similar argument, the lower densities of Jupiter, Saturn and Uranus relative to the Sun are explained by them having been formed as the result of a giant impact? (Of the outer planets, only Neptune is denser than the Sun I believe). I believe you also get an even more compelling...

Well, exactly! The creation method of the Earth-Moon system can be extrapolated to other planets, our and other solar systems, and even galaxies. I'm a big fan of Occam's Razor.

OK, thanks. It just seems ipso facto wholly inconsistent that the Earth-Moon system should have formed in one way and the solar system to have formed in a completely different way. BTW, can I ask how we have observational evidence if it takes millions of years for solar systems to form?

Could I just clarify: are you saying that the ignition of the sun could well have been the result of a collision with a (not necessarily large) body?

I'm very much an amateur with a keen interest in space/the universe and it occurred to me the other day that our solar system could have been formed in exactly the same way that it is hypothesised that the Moon/Earth system formed through the (proposed) collision of Theia and the proto-Earth...

By definition, I can't provide a meaningful reply to that question 8-)

So carbon fibre is a gas-permeable material (ie not "vacuum-tight")? But aluminium/stainless steel are not gas-permeable?

I am not wanting to actually design and build it: my questions were simply to establish feasibility. That is the fundamental pre-requisite of any project. Now that I know that it is at least feasible, I can progress from there in an appropriate manner.

Thanks guys for being so generous in sharing all your knowledge. I appreciate that I have been rather vague, but that's because I'm just trying to ascertain whether or not what I would like to achieve is technically feasible before attempting a proof of concept, and from what you've said it...

Or at least you can't put anything in or take it out while it's evacuated? :cool: As I said, basically at this stage all I want to be able to do is evacuate the tank without it collapsing. If 1mm thick material is fine - provided the design is appropriate (shape + bracing) - then I'm very...

Yes, buckling is my main concern. And I guess that will be an issue when using a cylindrical shape. Presumably an oblate spheroid design instead would be more robust?

I don't have an application as such yet. But as I said, at the moment I am just considering a single-piece vacuum tank with a pump attached to it - no access doors, windows, etc, just the pump connection point. I have no background in high vacuum. Leak detection does not seem to me a great...

I don't understand - why does the tank need to be mounted to something? And why could I throw the tank and the pump away if they are not connected to anything else? What am I missing? At the moment I am just looking into the hypothetical ability to create a single-piece vacuum tank that would...

Hi, Thanks for getting back to me. Let's say the tank is 50cm in diameter. I'm not sure what you mean by what the vacuum is connected to - the tank would just be connected to a vacuum pump in the air. Is there an equation that could give me some sort of indicative estimate of the thickness...

Hi, I'm hoping this will be a fairly easy question for someone on here to answer. If I wanted to make a (small?) vacuum tank (basically a hollow cylinder capped with two similarly hollow hemispheres - like so: (===)), how thick would the walls of the tank need to be for it to withstand the...