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Old Nov 7th 2017, 11:15 PM   #1
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How can stars be fixed?

Newton believed that a frame of reference fixed with respect to the stars is an inertial frame. But why fixed stars, when we know stars arent fixed they move as observed from redshift and we know universe is expanding?

Also tell me why newton used fixed stars as frame of reference?
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Old Nov 8th 2017, 02:15 AM   #2
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Simply because the observation techniques available in Newtons time
were not accurate enough to detect the movements of the Stars.
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Old Nov 8th 2017, 04:30 AM   #3
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Originally Posted by avito009 View Post
Newton believed that a frame of reference fixed with respect to the stars is an inertial frame. But why fixed stars, when we know stars arent fixed they move as observed from redshift and we know universe is expanding?

Also tell me why newton used fixed stars as frame of reference?
Back in the day, there was a lot of talk about the absolute frame of reference, which is the frame of reference that encompasses all other possible frames of reference and, consequently, affects the choices for how we treat the laws of physics observed in a local environment. However, that line of reasoning was ruined by relativity.
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Old Nov 8th 2017, 04:50 AM   #4
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However, that line of reasoning was ruined by relativity.
That line of reasoning was shown to be fallacious,
and relativity was developed to model the corrected view.
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Old Nov 8th 2017, 04:26 PM   #5
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Originally Posted by avito009 View Post
... tell me why newton used fixed stars as frame of reference?
Because in all practical terms they were , and still are fixed.

Observing the night sky their movement is so slow they appear not to move except for the movement due to the rotation of the earth ....

They form the backdrop which the 'wandering stars' , the planets move against..

The word planet is derived from the Greek for "wanderer."
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Old Nov 9th 2017, 09:23 AM   #6
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Even with better telescopes, etc. it is only the changing of the position of the earth in its orbit that would make stars appear to move over the period of a year. And that is only moving as compared to stars that are so far away that they appear to be "fixed" relative to each other.
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Old Nov 9th 2017, 09:57 AM   #7
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It is a question of the geometry of the viewing angle (trigonometry) that makes some of the closer stars appear to move depending on the position of the Earth in its orbit.

There are a very few relatively close stars that are moving across our line of sight at super high speeds where an actual speed for the star can be directly observed (using super accurate telescopic measurements).

see <Wikipedia:Hipparcos>
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Old Nov 9th 2017, 11:57 AM   #8
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Don't forget that a visible star will achieve transit once a night due to the rotation of the Earth.

This is the principal 'movement' observed.
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