e_j_white

e_j_white t1_j4kcf6n wrote

Reply to How do we know that we are in a certain place inside our galaxy? and how do we know how big it is just by looking at the cross section we are in? by friday_panda

Great answers here, just want to add that we don't "know" for sure. We're still trying to measure the size of Milky Way every year.

We thought it was 100K ly across, but some researchers in 2015 claimed it's 150K ly.

Just recently, a new publication is now saying it could be 200K ly across!

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e_j_white t1_j26wo0k wrote

Reply to comment by bitwaba in How fast does the Milky Way spin? How far does Earth move through space in a year? by Sabre-Tooth-Monkey

Nope, orbital speed goes down as you get farther away. The equation is:

v = sqrt(G * M / R)

Larger R, smaller v.

In order to REACH a higher orbit, you need to do work to move the mass to a higher gravitation potential. That type of work requires thrust, but once you're at the larger orbit, the speed is slower.

Conversely, to move CLOSER to the sun, you need "anti-thrust" to move lower in the gravitational potential.

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e_j_white t1_j26ocwx wrote

Reply to comment by swampshark19 in How fast does the Milky Way spin? How far does Earth move through space in a year? by Sabre-Tooth-Monkey

Yes, it's true.

The outer stars are moving too rapidly to stay in orbit, and under normal calculations they should be thrown out of the galaxy. Additional gravitational forces must be keeping them in orbit at those faster speeds, and that's where the theory of dark matter comes in.

For example, Venus is moving at 78K mph, while Saturn is moving at 22K mph (because it is much farther away from the sun). If Saturn were moving at the same speed as Venus, it would be thrown farther out from its current orbit.

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e_j_white t1_j12h0ux wrote

Reply to Does anyone feel trapped here by vapournova

If it makes you feel better, even if another big bang occurred trillions of year from now, you probably won't experience any form of existence again.

¯\_(ツ)_/¯

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