shyam Posted May 21, 2017 Share Posted May 21, 2017 Hi i ve been haunted with may be a foolish question, but never understood and may be feel a bit comfortable sharing my doubts. Forgive if its childish or foolish. Now let me come to the point. que: As understood Polaris is always stable as its on the center or axis so the rotation of earth dont deflect polaris away but earth also revolves around sun taking 365 day so does this so called north star remains constant . The earth is speed = 2×π×(149,600,000 km)/(1 year) thats the KM or AU travelled by earth in one year so does Polaris also travelling along with earth ? regareds shyam menon Link to comment Share on other sites More sharing options...
Mr niall Posted May 21, 2017 Share Posted May 21, 2017 No it's not foolish I wondered this a few years ago - the answer is that Polaris does move but it's like 400 light years away or something, so if you compare the total diameter of the path the earth takes around the sun and then compare it to a light source 400 light years away then you see that, in perspective terms, the movement appears so negligible that we don't really notice it. Sorry, if that's not a very good explanation it might be easier if you drew it. Think of standing on a harbour and looking at a ship on the horizon, the ship could really be zooming along but for you on the harbour it would take a few mins to be able to tell right? Now imagine that ship was just moving from side to side a bit, it'd be hard to tell right? Then extrapolate that a million million times! Link to comment Share on other sites More sharing options...
rockystar Posted May 21, 2017 Share Posted May 21, 2017 Mr Niall had hit the nail on the head, It's too far away for earth orbit to detect a shift. It's like the way we work out distance parallax - measurements are taken 6 months apart, and the shift is measured, but this only works for the closest few stars, and even then it's a very small shift Link to comment Share on other sites More sharing options...
Peter Drew Posted May 21, 2017 Share Posted May 21, 2017 It's been my understanding that Polaris is not central to the axis of the Earth's rotation and this is why you have to place polaris in a circle defining the offset when polar aligning with a polar alignment graticule. Link to comment Share on other sites More sharing options...
LightBucket Posted May 21, 2017 Share Posted May 21, 2017 12 minutes ago, Peter Drew said: It's been my understanding that Polaris is not central to the axis of the Earth's rotation and this is why you have to place polaris in a circle defining the offset when polar aligning with a polar alignment graticule. Absolutely correct, Link to comment Share on other sites More sharing options...
Stu Posted May 21, 2017 Share Posted May 21, 2017 The only thing to add is that over the long term Polaris is not constant. The Earth wobbles on its axis over a period of 26,000 years I believe, so in future Polaris will no longer be the Pole star. Link to comment Share on other sites More sharing options...
Saganite Posted May 21, 2017 Share Posted May 21, 2017 27 minutes ago, Stu said: The only thing to add is that over the long term Polaris is not constant. The Earth wobbles on its axis over a period of 26,000 years I believe, so in future Polaris will no longer be the Pole star. I won't waste my time aligning then Link to comment Share on other sites More sharing options...
Peter Drew Posted May 21, 2017 Share Posted May 21, 2017 1 hour ago, Saganite said: I won't waste my time aligning then That's the point, you don't align on Polaris, just the point in the sky near it, Polaris is just the best guide. Link to comment Share on other sites More sharing options...
Stu Posted May 21, 2017 Share Posted May 21, 2017 3 hours ago, Saganite said: I won't waste my time aligning then It will probably be around that time before the skies clear!! Link to comment Share on other sites More sharing options...
ronin Posted May 21, 2017 Share Posted May 21, 2017 4 hours ago, Stu said: The only thing to add is that over the long term Polaris is not constant. The Earth wobbles on its axis over a period of 26,000 years I believe, so in future Polaris will no longer be the Pole star. It will take that long before Synta get StarSense to operate and that just means they will have to start all over again. Seems Gamma Cephi is going to be the next Pole Star. at around 3000 AD (I think AD) it will be closer to the rotational axis the Polaris is at present. That will cause the IAU a problem as what will they call it ? Thuban appears to have been the previous good one. Past and future ones are indicated here as a simple diagram: http://earthsky.org/brightest-stars/thuban-past-north-star Link to comment Share on other sites More sharing options...
rockystar Posted May 21, 2017 Share Posted May 21, 2017 I believe Vega is a future pole star too. https://en.m.wikipedia.org/wiki/Category:Northern_pole_stars Link to comment Share on other sites More sharing options...
TareqPhoto Posted May 23, 2017 Share Posted May 23, 2017 On 5/21/2017 at 18:39, rockystar said: I believe Vega is a future pole star too. https://en.m.wikipedia.org/wiki/Category:Northern_pole_stars Should i align my mount with Vega just as future proof? It will be exciting to watch stars war for the pole throne, who will win, Polaris or Vega or maybe Arcturus? Link to comment Share on other sites More sharing options...
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