Stars' motion

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Stars' motion

Postby alright1234 » Thu Apr 11, 2019 12:38 am

Are the stars of the stellar universe including the Sun in motion or are they and the Sun stationary? If they are in motion (stars) then why do the constellation have the same shape?
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Re: Stars' motion

Postby Gfamily2 » Thu Apr 11, 2019 12:47 pm

alright1234 wrote:Are the stars of the stellar universe including the Sun in motion or are they and the Sun stationary? If they are in motion (stars) then why do the constellation have the same shape?


Hi, yes the stars in the galaxy are in relative motion - generally in orbit around the centre (which takes about 250 million years for the Sun), but they may also have their own individual motions on top of that.

The reason they appear in the same locations is that they are generally a long way from us, so their movement across the sky is not generally observable.

There's a great ESA video showing the movement of stars (based on real measurements) over the next 5 million years
https://www.youtube.com/watch?v=87lgSRVUSxM
Each second of the video is about 30,000 years and even then, most of the bright stars are only moving slowly.

The star that is moving fastest across the sky from Earth (Barnard's star - that is so dim you need a telescope to see it) takes about 400 years to move 1 degree across the sky, so its motion would be barely detectable to the eye even over a lifetime.
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Re: Stars' motion

Postby Aratus » Sun Apr 14, 2019 5:45 pm

Yes - you could easily go back 4000 years and the constellations would be indistinguishable from those of today. Go back 6000 years and only someone who knows the constellation shapes well, would notice a slight difference in some of them. You would need to go back 10,000 years to notice any significant changes.
I use an 11" reflector (Celestron CPC 1100) and a 3" refractor, (Sky-Watcher ST80) mounted on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI 120MM, ZWO ASI1600MC and Canon 1300D for imaging.
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