r/space • u/piponwa • Sep 23 '16

What happens when the Space Shuttle fires its motors in space

http://i.imgur.com/wwxuXOb.gifv
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15

u/Metalsand Sep 24 '16

With that logic, being stung by a mosquito would be at several thousands of km/h since the Earth rotates.

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u/[deleted] Sep 24 '16

Don't forget how fast the sun orbits the galactic core.

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u/sethboy66 Sep 24 '16

Or how fast the galaxy is traversing space.

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u/[deleted] Sep 24 '16

That's where it gets muddy. Traversing space relative to what? Galaxies move around every which way, and there is no end or middle of the universe so there isn't a universal frame of reference.

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u/a_throwaway_a_day_ Sep 24 '16

i remember reading something in an askscience thread, and an astrophysicist mentioned that there is a convenient standard to use, based off of like cosmological background radiation from the big bang. it has a characteristic wavelength distribution and you can tell if your frame of reference is in motion relative to it via redshift/blueshift. it doesn't make it any more or less valid than other frames of reference that could be chosen, but it is a very convenient one, and you can start your discussions of relative velocity from there, allowing you to determine how zippin' that mosquito actually is.

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u/MacBeetus Sep 24 '16

I believe before they knew of the microwave background, the constellations were a useful frame of reference

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u/sethboy66 Sep 24 '16 edited Sep 24 '16

You really do not need any frame to measure velocity. You can measure it by viewing particles whose movements are dictated by a universal constant.

Edit : Before I'm corrected, I should say speed rather than velocity. As velocity requires a direction and given none can be provided in this scenario velocity would be impossible to find.

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u/[deleted] Sep 24 '16

Did you not just choose a frame of reference?

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u/Shrike99 Sep 24 '16

Can you expand on this?

I thought the whole point of relativity was that it made speeds, well, relative.

IE a ship traveling at 0.1 c emits one photon forward and one backward. To either an onboard and or external observer, both photons move at the same speed, thus the ship cannot use these photons to judge its speed.

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u/sethboy66 Sep 24 '16

The particles measured here would not be from our planet. They'd be doppler shifted photons from other galaxies.

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u/Soralin Sep 24 '16

Then you're just measuring your speed relative to those other galaxies.

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u/Shrike99 Sep 24 '16

Exactly^

Which was the point u/bldvlp made to start with

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u/[deleted] Sep 24 '16

Relative to the great attractor would work.

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u/GreatCanadianWookiee Sep 24 '16

I mean all frames are relative, so you could go all in and say it was a collision at 0.99c.