Expanding Universe

[Bazile]

If the universe is expanding , is anyone / institution , constantly updating the information as to the distances between planets /stars / galaxies ?

[jim360]

Not really any need locally, at least -- the expansion rate is only visible over superlarge scales. Most galaxies nearby are moving closer to us, if anything.

Over the larger scales, meanwhile, I don't think the measurements are quite accurate enough to justify constant updates. On the other hand, the relevant parameter, the Hubble Constant, probably is meaning remeasured fairly regularly, especially over the last 20 years.

[Theland]

Like my waistline, the rate of expansion is unpredictable.

[Theland]

Jim - Some galaxies moving closer?
I thought ALL galaxies showed red shift?
New to me.

[Buenchico]

You'll have to start by defining 'distance'. It's not quite as easy as you might think!
http://curious.astro.cornell.edu/about-us/104-the-universe/cosmology-and-the-big-bang/expansion-of-the-universe/619-how-do-we-define-distance-in-an-expanding-universe-intermediate

Once you've decided on what you mean by 'distance' though, some fairly basic mathematics is all that's needed to keep track of things. (e.g. if I know that a snail that's currently 10m from me is moving away at 1m per hour then in 5 hours time I'll know that it's 15m away. I won't need to get a tape measure out, I can simply calculate the answer I require).

[jim360]

Yeah, TheLand, it's true. Close enough to us, local effects dominate. Some, most, or all of the nearest galaxies are moving closer to us, such as the Large Magellanic Cloud and Andromeda, which will collide with the Milky Way in about 2 and 4 billion years respectively.

[Theland]

Bloody 'ell!
I better not make any long term plans then.

[New Judge]

Indeed. Don't buy any green bananas.

[Theland]

May take out a big bank loan.

[Arksided]

Andromeda is going to collied with the Milkyway... gosh I'd better pack some spare underpants.

[Bazile]

Yes Buenchico .
But i dont want to do any calculations

If i open a text book written today it will say A is x amount of light years away from B

In for example 10 years time that info in the text book will be out of date .
So i want that text book updated or another text book written with the ' current ' information

[jim360]

If I remember correctly, the collision will look spectacular from like 3 million light years out, but close up it would be rather similar to the collision you'd get from two "crowds" of five or so people walking towards each other from either end of a football field.

[mibn2cweus]

Theland
Jim - Some galaxies moving closer?
I thought ALL galaxies showed red shift?
New to me. 17:05 Tue 15th Jan 2019

In addition to galaxies moving with space (due to expansion) galaxies also move through space. The Andromeda galaxy (a relative neighbour) is moving towards us and will eventually collide or merge with our galaxy (the Milky Way), easily overtaking the expansion rate given the relatively short time and distance involved.

[Old_Geezer]

There's so much gap between matter and so little matter, you'd probably not notice the merge were you there.

(Unsure if dark matter changes that.)

I believe the local motion is 'true' motion so can be either away from or towards; whereas expansion on larger scales is more likely to be apparent from space being created between the two 'objects'.

[mibn2cweus]

If we discover the centre of the Andromeda galaxy is headed straight for our Solar System . . . things could get interesting.

[mibn2cweus]

^ ^ ^ Always looking on the bright side.