November Entry: Dont Panic !

[Redrobes]

Been doing a little experimenting with sectors. It turns out that if we go with 100 angular segments and the bit to be mapped is on the edge then the space is very nearly cubic. As you get towards the center your angles have to increase obviously but in the center I would expect that you would change coord system to spherical since a) thats the arrangement b) the gravity there would be so immense that it would be hard to travel there and c) there would be zillions of stars there so its more of a cartographers problem than one of navigation.

So the coord system will be 100 angular units per circle and I will map 1 of them. Radially our milky way is 50,000 light years. The outer band in the image below is at 1/10th of the radius so for milky way thats 5000 light years.

List of closest stars..
http://en.wikipedia.org/wiki/List_of_nearest_stars
... means that we should have stars at about 15 light years apart or so. That means 5000/15 is 330 or so which is clearly too many to map (330x330x330)

(BTW that page has a diagram just like what I want to make but doing just a sector instead of a whole circle.

So as anyone who has star charts know they list only the brightest stars not all of them. What we would need would be the most relevant. This would mean those with inhabited planets, systems with planets possible to live on, or ones having a solid surface etc. You also need those which are big, bright and those which present a danger. We also need to mark on there outposts and non natural satellites.

So in the list of top 20 closest stars only 5 of them are of magnitude 5 or below but were still waaay off mapability.

Here is a great link to a web site with nearest stars in a 5000ly redius - perfect....
http://www.atlasoftheuniverse.com/5000lys.html
... except that it looks like clouds.

So either we need to map a whole lot less than 1/100th of the circle or we have to be far out on the rim of the galaxy or the galaxy has to be less dense or less compact than the milky way.

Might have to fudge it a bit and pic something conveniently out on the rim to give just the right density of star systems with interesting enough properties to map.

This is always the problem with astro stuff. The numbers are always just too big. I wonder if Torstan is going to do a map... now that might get interesting.

[torstan]

Thinking about it I'm a particle rather than astro person so I'm actually almost as in the dark about this as the rest of you. However I do share an office with people working on the Sloan Digital Sky Survey - probably the largest space map ever made - so I might well tap them for ideas.

Just one note on your thoughts on units - light years are a sensible measure of distance as light is the only thing with a constant speed in the universe so measuring distances by the time that light takes to travel is a sensible choice. Obviously the concept of 'year' is the thing that would change.

[Redrobes]

I was reading somewhere today that there are 6 septasqillion or whatever stars and the size of the universe is such and such and that therefore one divided by the other means that you get an average of 70 stars per lightyear cubed which is obviously very high. Knowing also that we are in a galaxy and that the distance between galaxies is vast then that implies that the number of stars in the center of a galaxy must be just extreme - astronomical in fact. So I gather that the white ball around the center of galaxies is just packed with stars in a very small space.

You have mentioned before that in black holes the gravity is so great that your head and feet get ripped apart from gravity gradients. If there are that many suns packed close enough together then presumably that same effect is true - or lets be more real, the distance across a star ship capable of getting to the center of a galaxy must have a considerable gravity gradient across it.

My question is: where approximately on the swirling disk of a galaxy is the gradient so great that its unlikely that a tough starship hull could possibly withstand the gravity gradient ?

Thats what I was getting at with the change from polar to spherical coords near the middle because I doubt any ship could go there. Even if the tech was around to create an artificial gravity field I would imagine that would take energy to do it and the energy consumption would be more than that of the capability of the ship.

<snip>

[torstan]

I'm a UK person in the US so I'm just a fascinated observer. I'll let the actual Americans answer the US electoral questions

Interesting question about the gravity gradients. I'd be surprised if you get much in the way of serious tidal forces outside of the central black hole's immediate vicinity. There are a lot of stars, and so gravity will be much stronger - but in freefall - ie when you are out in space - its only the difference in gravity between two points that makes a difference rather than the absolute value of gravity at a point. It needs to be changing pretty fast for that to have a significant effect and I'd guess that only something as exotic as a black hole will have those sorts of gradients in its vicinity. I know that's awfully hand wavy. If I get a chance I'll have a look at getting you something more precise.

[jfrazierjr]

I know that's awfully hand wavy

Hocus Pocus!