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Comment by rb808 | Hacker News Reader

Far out in the uncharted backwaters of the unfashionable end of the western spiral arm of the Galaxy lies a small unregarded yellow sun. Orbiting this at a distance of roughly ninety-two million miles is an utterly insignificant little blue green planet whose ape-descended life forms are so amazingly primitive that they still think digital watches are a pretty neat idea.

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Wouldn’t it be wondrous if the galaxy had plentiful intragalactic public transit and we don’t have access because we’re the planetary equivalent of the suburbs?

We just need to build a station in the neighborhood: https://www.technologyreview.com/s/613127/a-halo-drive-could...

This is kind of a plot element in Mass Effect, but the humans are lucky enough to have a stop in our system.

What do you mean the humans are lucky enough to have a stop in _our_ system?!

I think the Reapers may have arrived 167 years too early.

Come on giant space Cthulhus, we haven't even discovered the Prothean Ruins in Mars yet!

Did New Horizons categorically rule out that there's something hidded inside Charon?

my pet theory is that galaxies are more like fireworks wheels, and so we aren't strictly orbiting the galactic center, we're also slowly getting farther and farther from it (that also takes care of the dark matter conundrum in my view), and thus couple billions of years ago we were in the much better and more populated part of the town than the current 'burbs.

You are not very far from what could be the reality. According to some research the Solar System has 10% less hydrogen than other galaxies, so Bussard ramjets will have an harder time

What if dark matter turns out the key to a decent space drive? There appear to be galaxies without it (a good reason for believing it exists where there is evidence) and so any aliens there would be SOL.

Astonishingly enough, you might not be far off. That is the operating principle behind the Alcubierre Drive. https://en.wikipedia.org/wiki/Alcubierre_drive

Edit: Apologies, it seems it does not in fact use dark matter.

The Alcubierre drive relies on negative matter, not dark matter.

Unfortunately, Alcubierre doesn't use dark matter. It uses negative mass (or even imaginary mass) matter. Dark Matter is believed to have regular positive mass (if it were negative mass, we'd be wondering why galaxies seemed to have less matter than they should).

The existence of negative mass exotic matter remains an open question.

No doubt stolen by the untrustworthy Andromedites!

All the planning charts and demolition orders for it have been on display in the local planning department in Alpha Centauri for fifty Earth years

...in the bottom of a locked filing cabinet stuck in a disused lavatory with a sign on the door...

What do you mean you’ve never been to Alpha Centauri? Oh for heaven sake mankind it’s only four light years away! I’m sorry but if you can’t be bothered to take an interest in local affairs that’s your own regard.

It’s just going to be a bunch of NIMLICs at the meeting anyway (Not In My Local Interstellar Cloud).

'beware of the leopard'.

Or the wilderness

It's unlikely. Closer to the core there is too much radiation for life to be possible.

And farther away there are not enough metals.

As best as we can tell we are at the distance where all other life would be.

Suburbs intentionally avoid mass transit.

You are thinking of... a ghetto.

This is probably a really silly question, but how do astronomers and the like define "west" in this case? I assume it must be useful to have some sort of reference orientation for the galaxy, but how is it defined?

The directions are defined the same way as directions on the Earth or in the solar system using the right-hand rule to define north and east based on counter-clockwise rotation.

Ah, I forgot that the galaxy rotates as well. That definitely makes things a bit simpler.

It's a quote from The Hitchhiker's Guide to the Galaxy. Only hit me at the very end of it... "digital watches are a pretty neat idea".

West can be defined in terms of spin direction, but western ( as in hemisphere) requires a meridian to define the boundary. I'd have assumed that we'd have put Earth on the galactic meridian, much like the Brits put London on the terrestrial one.

I expect it goes through Greenwich, as always!

Okay, so once you have north, which way is east in a circle?

East on Earth is the direction in which we rotate. Should be the same for a galaxy.

That's because earth can be viewed as a plane. The galaxy can't, you need a median.

1. Milky Way is much more like a plane than Earth

2. it doesn't matter anyway any object which rotates can have direction named basing on that rotation

You are correct, it is determined by spin. However, for some reason that has never been explained to me, we define galaxies to spin in the opposite direction from planets.

I never thought about this. Will most solar systems form roughly on the same plane as the galactic disk, and will they generally have orbits in the same or the opposite direction as the galactic rotation of their star?

It's basically random; the rotation of a solar system depends on the rotation of the gas clump that collapses to form the star and its system, and that depends on local details about the relative orientation of local gas clumps, the possible influence of winds from nearby massive stars and supernova shock waves, and general turbulent motions within molecular clouds.

It's not very random. The galaxy also formed from a clump of rotating gas, and this heavily influences the direction all of the sub-bodies will rotate and orbit. Systems influenced by other forces would be the exception to the norm.

No, it is pretty random, just as the orbits of binary stars are randomly oriented. The scales of star and solar-system formation are much, much smaller than the scale of the galaxy, so the memory of the latter has been scrambled by all the intermediate and local processes.

From this Cornell "Ask an Astronomer" page (http://curious.astro.cornell.edu/about-us/159-our-solar-syst...)

"The size of a solar system is so much smaller than the size of the Galaxy, that the Galaxy's structure has no impact on the orientation of a solar system. What determines their orientations is the direction of the angular momentum that the system had when it formed, and that's pretty much random."

Or take a look at these ALMA images of protoplanetary disks (solar systems in the making) around pre-main-sequence stars. All are at very similar distances, and most are at very similar positions relative to the Galactic plane, so they should all show very similar projected shapes and orientations if they followed the galaxy's orientation -- but they are all over the place.

https://www.eso.org/public/images/potw1904a/

We don't define galaxies in general to spin in the opposite direction.

Just the Milky Way.

(The reason for this seems to be that Galactic "North" was defined long before we had the data to determine which way the Milky Way rotated -- or even that it rotated. By the time the rotation was definitively determined, it was too late to override convention. This may go back to William Herschel deciding that the "north pole" of the Galaxy should be in the same hemisphere of the sky that the Earth's north pole pointed toward. In retrospect, he had a 50% chance of being right...)

You can try Polaris

They don't, AFAIK. You can only get away with it if you're writing exceptionally goofy science fiction.

It's more like spinwards and widdershins, really.

Spinwise/turnwise, and rimwards :)

They use giant supercomputers to do simulations which results in these counter intuitive answers. The trick is to ask the right question.

Also the Galaxy song is funny and mostly accurate

http://www.montypython.net/scripts/galaxy.php

digital watches are a pretty neat idea. they're vastly more accurate than mechanical watches while using incredibly little energy.

Just bought a Casio digital watch this morning because it has a countdown timer you can adjust up and down. I'm a happy ape right now.

It makes me sad how many of the replies here seem to have completely missed the reference. The fact that it's upvoted to the top gives me some hope, at least.

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