How and why is the big dipper changing?

[judge fear]

Hi everyone, I write this due to in the program called Stellarium I noticed something odd when looking at the big dipper constelation:

In this program you can see the sky how it is today but also in the past and in the future and how the stars will have moved and such.

When I looked at todays date and then forwarded to the year 900000 I saw the big dipper now looks different than it does now and is now trying to find out why and what is causing that to happen?

Looked in my astronomy book and came up to these theories:
- stars located nearer the milky way galaxy center moves faster than the stars near the border, a so called differential motion, when I look on big dippers stars I see alkaid and dubhe is further away than the other 5 stars in it, could that be the reason for it? I dont think so since those stars and earth is located pretty near in our area of milky way so the effect shouldnt be that apparent but I could be wrong.

- Stars move in their own orbits and travels in different directions and after a long time the star signs will start to change as the stars is moving closer/farther away from each other and in this case dubhe and alkaid belongs to a different cluster of stars than the other 5 and is travelling a different way.
Note: According to a friend of me says this is wrong and the stars are orbiting in the same direction in the milky way of the gravitation and something else is doing this.

- Proper motion is the cause of this and why we on earth seems to see stars moving from each other, this is an effect one can see with the closer stars in comparison to stars farther away.
But isnt this still that stars are moving or how does proper motion work?

Or could someone explain how this work and why the big dipper looks like its stars are moving and what is the cause of it and how?


Here is a good picture showing what I see in stellarium.

This website explains it a bit but not much how proper motion work and why some stars more in one direction and the others in the opposite:
http://www.lunarplanner.com/StarsProperMotion/UrsaMajor/index.html
But in the text they say the stars are moving when the person who works as a teacher in astronomy says othervise :S

Asking here for help to understand whats happening?

[Owmuchonomy]

Alkaid and Dubhe are moving in a different direction to the other 5 main stars. Ultimately this will change the appearance of the Big Dipper. The asterism is purely for our convenience and as is common the stars comprising it are not related to each other.

[ronin]

Some of the stars started out in the same cluster so are slightly bound, others are nothing to do with it and just happen to be where they are to make the pattern we see.

Over time they will both drift along and drift apart, those not part of the original cluster will amble off some other way. Also we are circling the centre of the Milky Way, and over time will be at a different position, just takes a while.

In effect and simplest it is all moving and the includes us, nothing is fixed.

[Tinker1947]

Around 40,000 years I think its Vega becomes the pole star, stuff moves, while not in your life time many are travelling  very fast 100's of miles per second, you won't notice any change.....

[Kropster]

All the stars are moving, each at a different speed. Over time the patterns we call 'Constellations' change due this movement.

Constellations are just the pattern of stars that we see from Earth at our particular moment in time. The stars themselves are not linked in a fixed pattern as they travel through space.

[judge fear]

Around 40,000 years I think its Vega becomes the pole star, stuff moves, while not in your life time many are travelling  very fast 100's of miles per second, you won't notice any change.....

That is due to earths precession, due to the sun and the moons gravity pull earth making it to wobble like a top and the pole makes an circle on the celestial sphere which takes 26000 years to make a complete circle, hence the polaris star wont be in the north and vega star will be, its not that the star polaris move but earth in this case.

Thanks for the replies but I suggested that before: that the stars moves in the galaxy, in the case of Big dipper the 5 stars are in a cluster while Alkaid and Dubhe isnt and has a different orbit and with time those 5 stars will be moving away hence changing the constelation.

But that dont answer why some of these stars moves faster than the others, shouldnt they move equally fast? A person I know mentioned that these stars dont travel in the galaxy but has slightly different orbits as they rotate around in the galaxy as out sun does.

According to that and some sites I found proper motion is one reason behind this and why stars from our viewpoint on earth looks like changing:

http://www.astro.virginia.edu/class/majewski/astr551/lectures/VELOCITIES/velocities.html

But I dont manage to grasp how proper motion works and is completey.

[Kropster]

It would be surprising if stars traveled at the same speed and in the same direction as each other. 

Gravity acts between all objects and any given star has gravity acting on it from lots of different directions and at different strengths to other stars.

They may swirl around with roughly the same speed as neighbouring stars, but in the mix there will be variation...especially after a galaxy collision or near miss.

[judge fear]

Very true and after some research I only find prof for them moving in different directions and varying speeds, but its not huge differences but they do as you say.

Oh you are from oxfordshire?

[Kropster]

Very true and after some research I only find prof for them moving in different directions and varying speeds, but its not huge differences but they do as you say.

Oh you are from oxfordshire?

Yes, Oxfordshire.... but we aren't all University Professors here!!

[judge fear]

Yes, Oxfordshire.... but we aren't all University Professors here!!

Hahaha xD I react due to I lived there for some time and been there on some visits and have some friends who lives there So yeah I am aware not all are professors there xD They have an excellent geology group and interesting science things there