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hi im ash from north wales. I've been interested in astronomy for years but never really known anything, im still not convinced. i've recently bought a book called patrick moores teach yourself astronomy which i find quite interesting. I was told that data in astronomy is always changing so it says in my book that the andromeda galaxy is 2000 light years away, would that information still be the same in a few days or the next day from when i read it? ? It also says that polaris is 620 light years from earth. im confused, since i was told that data always changes in astronomy i dont know what books to believe.

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Andromeda is actually about 2.5 million light years away, but that won't change much in the next few years.

I know what you mean though. When I did some astrophysics modules at university we were told that 90% of what he was telling us would be wrong within four years. That was 15 years ago. The trouble is, the science is evolving all the time, both in technique and in results. So some things can change quite quickly. But the distances to well known stars such as Polaris, probably won't change much.

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What changes is the accuracy of the data we have and the conclusions drawn from it.

Andromeda is so far away that changes in its distance caused by its own velocity are insignificant to us, at least in our lifetimes, even in say 1000 years it won't have done much. What may alter is that through new techniques we are able to more accurately determine the distance that it is away. And so the data changes. So perhaps the distance was thought to be 2000 light years and we now think it may be 1800 light years. Just more accurate measurements.

The same holds true for many other things, Hubble Constant being one. Think it started out at about 80 and is a more accurate value is now considered to be around the 71 mark.

Polaris is a star and will have some movement relevant to us. Again over time it will move, again the movement is slow. Think that 2500 years ago another star was the Pole star (Polaris ?) so in 2500 years the stars have altered position. In another 2000 another star will be Polaris, but in 50 years time it will still be Polaris.

Polaris is a star in our galaxy, so closer. Andromeda is another galaxy a lot further away.

The timescales involved are long, very long.

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so distant objects outside our solar system dont move much so their data wont change, so how do i get the current info on how many light years a star is? Do i just accept the data patrick moore gives in his book eventhough the information may be wrong, like andromeda is 2000 light years away or so, and polaris 620 light years away? is there a website to get the right information??

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so distant objects outside our solar system dont move much so their data wont change, so how do i get the current info on how many light years a star is? Do i just accept the data patrick moore gives in his book eventhough the information may be wrong, like andromeda is 2000 light years away or so, and polaris 620 light years away? is there a website to get the right information??

Which Patrick Moore book are you reading ?.

I've got some of his from the 1970's and even then it was clear that the Andromeda galaxy (Messier 31) was over 2 million LY's away :)

Edited by John
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hi im ash from north wales. I've been interested in astronomy for years but never really known anything, im still not convinced. i've recently bought a book called patrick moores teach yourself astronomy which i find quite interesting. I was told that data in astronomy is always changing so it says in my book that the andromeda galaxy is 2000 light years away, would that information still be the same in a few days or the next day from when i read it? ? It also says that polaris is 620 light years from earth. im confused, since i was told that data always changes in astronomy i dont know what books to believe.

FWIW I would say don't get too hung up on the details. All deep space astronomical distances are almost best guess approximations anyway.

If Andromeda is 2 or 2.5 light years away does it really matter. It's still a vast unimaginable distance.

For up to date data the best you can do is stick to recent publications or glean a concensus from a number of good sources on the net. Wikipedia is a good general source to consult first, but good old Google will give you more data than you would ever need.

Edited by nebogipfel
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Hi Ash - as an analogy - if you look at a plane taking off at the airport it's going fast and flys away quickly. If you look a plane when it's 40,000 ft in the air and tens of miles away, it appears to be flying slowly accross the sky.

Well the same is true of objects in space except the scale is ramped up big time to light years. In fact - it's so huge a scale that objects in the sky when you were born will still appear to be in the same place when you pop your cloggs (though in reality they've moved a tiny bit).

I'd say don't worry too much about scientific measurement for observing purposes :)

Edited by brantuk
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I can't agree that 90 percent of what you might learn today will be wrong in four years. I'm sorry but I think that is utterly absurd. In terms of detailed measurements, these can and will change as techniques are refined and cross checked. But in terms of the big picture, no.

Let's think about Andromeda. There was a 'great debate' going back about 150 years as to whether or not the 'spiral nebulae' were really distant objects or relatively local and within the Milky Way. For a long time there was no way of knowing, then in the 1920s Hubble found a way to estimate a distance to M31 Andromeda. He used a type of variable star, a Cepheid, to do this. His distance put the Andromeda nebula way beyond the Milky Way. That has not changed, and it won't change other than that the two galaxies are falling towards each other. But during WW2 Walter Baader found that the stars Hubble had used to get his distance had two different forms and that Hubble's distance was wrong. But how wrong? It did not change the fact that Andromeda was an external galaxy not part of the Milky Way.

There is that joke about the museum attendant who was asked how old a dinosaur skeleton was. 'Why ma'am, it is 70 million and two years, three weeks and six days old.'

'Oh my, how can you be so precise?'

'Well ma'am, it ws 70 million years old when I started this job two years, three weeks and six days ago...'

Anyway, terms like 'wrong' can be naive in science and the serious scientists that you will read would not use those terms. They talk of models that are as good as we can get them. These models are always up for review and nothing pleases a real scientist more than being able to break an established theory because this opens the door to new and exciting ways of describing nature.

Olly

Edited by ollypenrice
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In Star Atlas, such as Nortons, time is measured in an Epoch, and the time span is 50 years. That is how long elapses before they change the coordinates of the stars in their Atlas. It is 50 years, but most of them have changed very little in that time, because their distances are so vast. Plus they are not all moving in the same direction relative to us.

All things in the Universe are moving. All things have a proper motion.

Most of the objects you will see with your naked eye in the night sky, belong in our galaxy. One exception in the Northern hemisphere, is Messier31, the Andromeda Spiral Galaxy, which has been stated here at over 2.2 million light years distant. Andromeda is in fact on a collision course with our own Galaxy, the Milky Way. It is visible with the naked eye as a faint patch of light, top left of the Square of Pegasus.

Don't worry about it though, that event won't happen for millions of years.:)

Ron.

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