Long term galactic movement

[Traab]

An odd question occurred to me. We have a fairly accurate picture of what the milky way currently looks like I presume. Will things remain mostly static with the shape and position of the stars relative to each other? Or will they alter significantly over time? So in say, 100 million years, will the milky way look noticeably different than it does now? I remember reading that eventually our galaxy and the andromeda will pass through each other, so I would imagine that will have an effect on things, but will the milky way remain relatively the same until that happens?

[tomandtish]

As I understand it (and I am NOT an expert), the basic shape will stay the same barring something we haven't foreseen (which is quite possible).

Incidentally, the more recent models suggest that Andromeda and Milky Way will not just pass through each other, but will eventually combine (http://www.space.com/15947-milky-andromeda-galaxies-collision-simulated-video.html).

[Traab]

Heh, either way, whether they pass through each other, manage through some obscene twist of fate to crash into each other causing an intergalactic claymore mine effect, or merge together, it will be one heck of a hoot to experience. Too bad I will be a bit too old to enjoy it. :smalltongue: Wont our sun go red giant by then anyways?

[Seppl]

100 Million years will give all the stars a good shuffle as the stars orbit around the galactic center at different speeds and there are even additional velocity perturbations. Even a few thousand years are enough to amount to visible differences in the night sky, in 100 million years you will recognize almost nothing you know now. The solar system will also have moved about 180 degrees around the galaxy, so even the view outside the galaxy will be different as one could see all the things that are currently hidden behind the Milky Way and vice versa.

On the other hand, 100 million years is next to nothing on the time scale of galactic evolution. Some nearby dwarf galaxies will be visibly more torn by the Milky Way after that time but the complete "swallowing" of such a galaxy takes way longer than that. To an outside observer, the Milky Way will look completely unchanged (unless humanity starts doing some Kardashev III stuff), only the stars will have rotated around the center (and notably, the arms do NOT rotate with the stars).

By the way: The exact structure of the Milky Way is not actually that well known compared to other galaxies, as our view from the inside makes it hard to discern many things. For example, it was only 10 years ago that it was confirmed that the Milky Way is a barred spiral galaxy (and not a "normal" spiral galaxy).

[Max™]

The arms are like stellar traffic jams, as stars move around you get local areas where they bunch up and areas where they spread out.

Most of the stars we see in the night sky are surprisingly close and they all have a range of velocities relative to our own, there is no way the night sky would be remotely similar within a megayear, much less a hundred of them.

http://news.discovery.com/space/history-of-space/changing-constellations-50000-years.htm

[Telok]

Those familiar Greek zodiac constellations were set up roughly 3000 years ago and attached to dates, if I remember correctly. Today the stellar position has shifted by about a month, so when you were born the sun wasn't in your sign it was in the next one over.

[Closet_Skeleton]

The classical/astrological Zodiac (aka what you get in Newspaper Astrology, that ancient art invented in Britain in 1930) are arbitrary equal divisions of the ecliptic and are inaccurate not because things have changed since the GreeksBabylonians set the thing up but because they have nothing to do with where the constellations are, they're just named after constellations that are roughly associated. The constellations will have drifted away from where the Babylonians and Greeks saw them, but that doesn't matter.

The signs of the Astronomical Zodiac are based off where the sun is and have the same names as the Astrology Star Signs (+ Ophiucus) are based on where the sun is in the sky, and that would change a little. But the Babylonians never calculated that, so it hasn't changed at all since it was measured and written down (by coincidence? also in the Halcyon days of 1930).

But the position of the zodiac from earth is much more affected by Precession (how the earth wobbles during its orbit) than by the stars moving. That has thrown the Babylonian Zodiac off by about a month for reasons completely unrelated to the galaxy.

[Telok]

Seriously, I'm supposed to be a Gemini and the sun is in Taurus or Gemini depending on which of the three different zodiac calendars (https://en.wikipedia.org/wiki/Sidereal_and_tropical_astrology) you use.

It changes by a day every 70 years or so.

[Max™]

Seriously, I'm supposed to be a Gemini and the sun is in Taurus or Gemini depending on which of the three different zodiac calendars (https://en.wikipedia.org/wiki/Sidereal_and_tropical_astrology) you use.

It changes by a day every 70 years or so.

Nice, Leo is much cooler than Virgo, but heck with all that. I noticed once when the missus asked me about the Chinese zodiac figurines in Animal Crossing that we have the coolest kung fu manga/manhwa name ever from our birth years.

We are Iron Monkey and Water Dog!

[BlueHerring]

Those familiar Greek zodiac constellations were set up roughly 3000 years ago and attached to dates, if I remember correctly. Today the stellar position has shifted by about a month, so when you were born the sun wasn't in your sign it was in the next one over.On this same subject, the pole stars themselves will rotate out over time because of this. Thuban was the closest at around 3000 BC, and Alrai will be closer than Polaris in about another thousand years, at which point Polaris takes a step back for about 25,000 years.