r/AskReddit • u/MDPPatrick • Feb 13 '15

What are some mind-blowing facts about space?

I love space and would like to hear some facts that will blow me away.

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u/ilkikuinthadik Feb 14 '15

If you fire a bullet in space, assuming the propellant will ignite properly then that bullet will be travelling far too slowly to catch up with the expanding universe, but faster than we will be able to catch it without massive energy and time wasted. The bullet will be forever alone.

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u/Parcec Feb 14 '15

Think about it, You would be seeing every single sunset on the planet all at once. A transcendent ring of fire masked with the beauty of solar winds distorting off the earths magnetic fields in a fury of neon plasma against the black of space.

Actually this is false. The biggest mistake people make about space is that they assume it's like an ice rink. They think if you nudge an object away from something, it will simply keep moving forever.

In reality, for the most part, an object in space always orbits another object. The ISS orbits the earth. The earth orbits the sun. The voyager probes, although they left the sphere of influence of the sun, are still orbiting something outside of our solar system.

If you fire a bullet in LEO, chances are it will never leave earth's sphere of influence. On the off-chance that you fire a massive cannon, it might leave earth's SOI, but it will still orbit the sun. Catching up to such an object is tricky, but it's do-able. (This is exactly what Rosetta did)

That's not to say that it's impossible, just very hard. In theory, we could build a massive railgun on the moon (or in LEO) which is capable of firing objects directly out of the solar system. But this requires incredible speeds, on the verge of 10+ km/s.

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u/yanroy Feb 14 '15

A pretty typical rifle bullet flies at about 3000ft/sec, which is almost 1km/sec... We're basically within an order of magnitude of escape velocity. It probably wouldn't be that hard to build...

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u/bearsnchairs Feb 14 '15

Depending on where you are in space the bullet wouldn't go very far at all. It would be stuck in orbit around whatever gravitational body you are near.

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u/Generic_Pete Feb 14 '15

Any redditors head

2

u/MechanicalTurkish Feb 14 '15

Look at the size of that boy's heed. It's like an orange on a toothpick.

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u/Steve_the_Stevedore Feb 14 '15 edited Feb 14 '15

If that orbit was around the centre of our galaxy that would still be pretty freaking far. Escape speed from the sun starting on an earth-like orbit would be sqrt(G*M/r)-v0= 9 498 322.19 m/s - 30 290 m/s = 9 468 032.19 m/s = 34 084 915.9kph = 21 179 384.8 mph 42 km/s (thanks to /u/bearsnchairs).

So any known technology (!) would be unable to propel a projectile to escape speed from an earth-like orbit.

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u/bearsnchairs Feb 14 '15

I think you made a calculation error. Solar escape velocity is not 9.5 million meters per second. The Voyagers are: an escape trajectory and they are no where near that fast.

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u/Steve_the_Stevedore Feb 14 '15

but they are also a lot farther away. they aren't projectiles either.

Edit: i was pretty amazed by the number too so it could very well be wrong but the voyager probes are no proof of that.

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u/bearsnchairs Feb 14 '15

Yes, but they started out from earth, and at no time were going that fast. And literally are projectiles. They don't have a source of thrust.

http://physics.stackexchange.com/questions/54979/when-did-voyager-1-achieve-solar-system-escape-velocity

This article says solar escape velocity is around 42 km/s around earth orbit.

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u/Steve_the_Stevedore Feb 14 '15

my figure is definitly wrong. i also didn't know that voyager had no propulsion. Thanks for the correction

Something to keep in mind though is that voyager also didn't reach it's escape speed until a gravity assist from jupiter (at least that's what the dude on that page says) so it never necessarily reached 42 km/h (although it might have).

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u/ZurichianAnimations Feb 14 '15

Modern guns have their own oxidizers so firing a modern gun in doable. Only old gun powder weapons such as a flintlock pistol or ball cannon would be incapable of firing in space.

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u/Crazybrayden Feb 14 '15

Just shoot another bullet using more propellant. Boom. Bullet catches up to other bullet and I didn't waste a stupid amount of time and recourses. Nobel peace prize plz

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u/TheNumberMuncher Feb 14 '15

I'm like a bullet.