Milky way galaxy

Eventually yes, there will not be enough H and/or He to undergo nuclear fusion and no more stars will be formed.
That's a long long long way off as yet, and our own Sun will have long gone along with EARTH.
And no, the the earth was still not formed before the Sun, and any light from the previous S/N would have faded and not be worth much.

 

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What? No. I never said that. Not in so many words at least.

Our magentosphere protects us from the solar wind. This has in-turn protected Earth's atmo from being blasted off. Recent studies indicate that indeed, it is the solar wind that has stripped Mars of much of its atmo.
But here we are talking about light gasses. This is really about the later effects on the planets - after they cooled to rocky bodies, and after those rocky bodies outgassed.


The processes that turned the inner planets into rocky bodies in the first place - with Earth being mostly iron and nickel - would have occurred when the planets - and sun - were first forming.

 

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Well, not quite so simple. It is by no means guaranteed that all hydrogen will end up coalescing in a star somewhere. Likely a vast fraction of molecular hydrogen will remain for aeons after the last star forms. The corollary of which is that stars may indeed stop forming even while there is lots of hydrogen round.

 

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Can anyone give some idea, how the shape of Milky Way is derived ? After all we are inside it, what are the key and crucial observations which confirm the spiral structure of milkyway with bulge...

 

Well, we see that there is a very high concentration of stars in a very thin plane (this is the ribbon also called 'Milky Way' that can be seen with the naked eye across the night sky), and in the direction of Sagittarius, we see a large bulge in that thin plane. We can also tell how faraway that bulge is. Except for that thin plane, we can see out of our galaxy very easily in almost any direction due to the paucity of stars toward galactic north and galactic south.

Further measurements of distance, direction and density build up a pretty good picture of the shape of our galaxy.

 

The galaxy it supposed be 100000 light year in dia meter and 28000 l/y thickness, are we on the surface of the disk ? to see the bulge ? how far away are we from the bulge . Do at any time we aproach the bulge ( which I assume the bulge will be the mist lite area ?

 

The 28,000L/years thickness applies to the galactic bulge and we are situated towards the outer edges of a spiral arm.....and your third query has been previously answered.

 

We're about 27,000ly from the centre. The disk is about 10,000ly thick where we are - we are fairly near the centreline. We do not appreciably move toward or away from the centre - any more than most planets do around their sun.

In this diagram you can see
- our position in the Orion arm
- a conical area that is obscured behind the galactic centre
- other areas (dotted lines) that we cannot see but presume
- the orientation of the galaxy's bar

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Do you have a link to the source of the diagram?

 

Very informative . Thank you.

 

It's just Wiki
https://en.wikipedia.org/wiki/Milky_Way

 

The background for the wiki model seems to be a four armed symmetric spiral model and the following paper on 'The Spiral Structure of the Outer Milky Way in Hydrogen', in figure 4 part B, describes it as another fit for the four armed logarithmic spiral (figure 4 part A) that is also possible from their data.
http://arxiv.org/abs/astro-ph/0605728v1