How to measure the tangential component of velocity of receding starsor quasars?

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SUMMARY

The discussion focuses on measuring the tangential component of velocity for receding stars or quasars, emphasizing that redshift measurements only provide the radial component of velocity. It is established that nearby stars exhibit both radial and tangential motion, with the tangential velocity measurable through positional comparisons over time. The method involves determining the distance to the star and calculating the angular movement using trigonometry. The distinction between recession speed, which is purely radial due to cosmic expansion, and individual proper motion is also clarified.

PREREQUISITES
  • Understanding of redshift and its implications in astrophysics
  • Familiarity with trigonometry for angular measurements
  • Knowledge of General Relativity and its impact on cosmic expansion
  • Experience with astrometric techniques for measuring stellar positions
NEXT STEPS
  • Research methods for measuring stellar proper motion using astrometry
  • Explore the principles of General Relativity and its effects on cosmic velocities
  • Learn about the techniques for calculating distances to stars, such as parallax
  • Investigate the use of telescopes and imaging software for long-term positional tracking
USEFUL FOR

Astronomers, astrophysicists, and students interested in stellar dynamics and the measurement of cosmic velocities will benefit from this discussion.

aniketp
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Hi all,
How to measure the tangential component of velocity of receding starsor quasars?
I ask this because the velocity determined by observing the red shift will give only the radial component...
Thnx for replying...
 
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aniketp said:
Hi all,
How to measure the tangential component of velocity of receding starsor quasars?
I ask this because the velocity determined by observing the red shift will give only the radial component...
Thnx for replying...

nearby stars, like in our galaxy, are not receding from us as part of the general expansion. they just have their own individual motion, with radial and tangential components

tangential velocity of nearby stars in our galaxy can be measured by comparing positions over the course of many years
one figures out the distance to the thing, and one measures the tiny angle it moves per year, and uses trig. (multiply the distance times the angle in radians rate of change)

recession speed----that due to the expansion of distances a la General Relativity----is different from usual velocity. It only has a radial component. There is no tangential component to measure

a distant receding object can also have some individual proper motion. But this is often small compared with recession speed and may even be neglected.
 

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