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.
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?
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.
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.
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.
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.
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.
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.
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.
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...)
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.
"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.
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.
Slightly offtopic, but what extraordinarily well done alt text for the major images on this page. An example:
> "The most current map of the Milky Way is shown in an artist’s representation. The Sun is directly below the galactic center, near the Orion Spur. The Scutum-Centaurus arms sweeps out to the right and above, going behind the center to the far side."
They aren't quite following best practices with attribute usage, a screenreader may read both the alt and the title text for example and they're the same here, but to have the level of detail is really commendable.
It's also a really good example of how captions (this is a caption really, not exactly alt text) are context-dependent.
The caption you mention continues:
> The maser observed is almost directly opposite the Sun from the center in the S-C arm, 65,000 light years away.
...which makes no sense (there's no maser visible in the image or mentioned in the article) until you realise that this image was uploaded for another article and is being reused here.
Evidently the website's content management system asks for caption text when uploading the image, rather than when selecting it for use in the article. The latter is the right way to do it.
One of the local programming forums I frequented was also frequented by a blind guy who had an audio web device. His most frustrating experiences were sites that put the same thing in the title and the alt text. Unfortunately his device always had to read both, because so few websites actually followed the correct practices.
Off topic, but after my daughter was born I realized how sad and worried I was that she wouldn't be familiar with looking up at the sky on a clear night and seeing the Milky Way. Stuff like what's in this article is much more intuitive if it's part of your schema of the night sky; it's more difficult to appreciate when it's invisible.
She's too young to appreciate it now when I point it out to her when we have the opportunity, and I worry that when she's old enough to appreciate it she'll be someplace she can't see it. For me it was a common thing up until I was a bit older, and now it's uncommon to be in the right place at the right time to see it. I wonder if the unlit night sky will become something like old-growth forests or other ecological sights that are long gone.
Go to the Southern Hemisphere, the stars are still epic there.
Story Time: I'm from Australia, but didn't got for almost 10 years. I lived in the Yukon, roamed all of Alaska, etc. etc.
When I got to Australia after 10 years I walked outside in the middle of a city of 50,000 people and almost fell over the stars were so bright and colourful and (seemingly) close. They were so good, in fact, I took photos right there in the middle of that city that are better star photos than anything I have ever taken in Yukon/Alaska.
My most breathtaking glimpse of the world: Stopping one night while hitching through the Nullarbor, and walking to the coast very close by. Pitch black, but then not quite, for all over the sky were insanely more and brighter stars than I have ever seen before or since.
And then the crashing waves at the foot of the cliffs, and wind roaring in from the south, with the just the right amount of arctic chill to make it awesome and remind you that across that ocean lies Antarctica.
That's more than thirty years ago, but words about 'the end of the world' still take me back.
Can confirm that the Southern sky is great from my time in South Africa. We had a nicer view of the milky way during many braais in a small town backyard than I have seen in the Northern hemisphere (including back country camping in Yellowstone National Park). The combination of high elevation, dry air and little light pollution is great.
The most incredible night sky I've seen is on the top of Mt John (there's a small observatory) on the southern island of New Zealand. Mauna Kea wasn't close.
You could see the band of the milky away across the sky. It was like something from Hubble.
There's nothing like looking up in the sky and getting some perspective.
So yes, when I lived in the Europe one of the joys of coming back to Oz for holidays was that you can actually see stars. Even inside a big city, the nights tend to be clearer than in Europe and the light "pollution" more limited.
That said, I've never seen the Milky Way.
I probably could if I went out somewhere far from the city, but I can't remember ever actually seeing it, even when doing star-gazing at school camp.
Interesting. I think I've heard that before somewhere else. I'll have to ask one of my colleagues about it.
Where my family is from, in the northern US, the night sky is very clear and visible (barring clouds etc which aren't uncommon for various reasons). But where we live you can barely see much other than the moon and planets. I wish more attention were paid to light pollution.
I never really saw it, until I was about 18 and spent a weekend in the Swiss Alps. That was in the mid-'80s. I'd seen it as a dim smear before, but not in its full glory. It looked like the pictures. I wished I could jump on a spaceship and just head out there.
Skies in the alps (at least french and swiss) have too much light pollution to have properly clear picture most of the time. Every valley has some village, and even if you get to 3000+ metres (or even 4000+), glows from valleys are never too far. Depends on cloud/haze situation too.
I camp up there a lot, all seasons, even have full frame camera with tripod with me for night shots but you simply can't escape the glow (at least I didn't manage so far).
But to be honest, even in himalayas 2 years ago (3 passes hike in Everest region), or on Aconcagua (6000m camp) last winter the skies were mostly just OK. Of course with 30-second exposure things come to light, but I don't like those overly-photoshopped pictures of milky way so popular these days. Very little reality, too much painting with brushes with regard to color representation.
I'm from the inner city. Growing up, I always recalled just seeing a twinkle here and there in the night sky.
However, my mother's side of the family is from the deep south. I remember visiting relatives, and one time staring at the night sky. There were so many "things up there" I was both in awe and a little bit frightened.
Indeed! It is that sight, the infinity of stars and space, that has probably been the greatest creative inspiration for humans ever since we gained sentience. The reminder and assurance that there is more to reality than the artifice of society and its petty concerns we've cocooned ourselves in.
With the stars gone from the skies in cities and their surroundings it is truly a dystopia, where humans will live their lives out thinking that our cities are all there is.
When I was a kid, in the back of a sci-fi magazine I saw a t-shirt advertised, with a picture of the galaxy. It had an arrow pointing towards the edge saying "You are here." And another arrow pointing to the center, saying "All the action is here."
It's not easy to define a gravitational acceleration for the milky way since for planets it's defined on the surface and the milky way has no clear boundary per se.
That said, the escape velocity of our galaxy is 537 km/s; almost 50 times that of the earth. Most of it is due to dark matter.
Can you clarify the question? Big G is a constant everywhere. I can't think of an equivalent for little g (9 81). If you chose to define something it would depend where you are.
I meant the galactic centripetal acceleration we're experiencing (which I saw as the analog of little g, but I guess it isn't really); sorry if that was confusing.
As experienced on earth, as in during the day vs during the night? (I don’t know which side is facing galactic center but I’m sure it’s almost half the day one way and almost half the day the other way.)
I'd want it to be invariant to the time of day, so I guess as experienced by Earth's center? Or the sun's center. Just wanted a vague ballpark number, which someone already mentioned.
this is very surprising, considering that you can actually see it with your own eyes at night and it is not spherical at all. There are also countless panoramic photos of the whole thing, which always look more or less the same, and there is no way it can be spherical. See for example https://www.eso.org/public/images/eso0932a/
It may well be, with the vast majority of the solar mass in the visible disk, and a handful of stars too dim to easily perceive forming a sphere. The Andromeda galaxy actually takes up a sizable portion if the earth’s sky in its full extent, we just don’t see it.
The period of the vertical orbit is closer to 1/3 that of the planar orbit: roughly 70 million years, versus about 225 million years for the azimuthal ("horizontal") period. Since the periods aren't in an integer ratio (and you wouldn't generally expect them to be for galactic orbits), it's also not neatly closed like the schematic suggests.
The article is about how much above or below the plane, specifically the central plane of the galaxy we are. Spoiler: We're currently above (north) of the central galactic plane by tens of light years, and still traveling upwards, but it's cyclical and we'll be below the plane again in a few million years.
