Questions on the Movement of Stars

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In summary: I'm looking forward to more theory questions in the future!In summary, it appears that a star's velocity can't be directly measured, but it can be inferred using the Doppler effect. If the star is displaying a redshift or blue-shift, it might be due to gas being expelled or absorbed, or due to gravitational effects. However, if the redshift is cosmological, it might actually mean that the star is at rest.
  • #1
stardrop
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01. Can a star be moving faster than what Doppler effect calculations indicate? This was a discussion question I heard but I'm not sure I understand. Can anyone provide any sort of information about this?

02. Can someone explain this to me, too? "Hydrogen red line is shifted, but other observations make the star appear to be at rest". It's described as an anamoly, but I don't get it. :cry:

Even just seeing links somewhere on the internet would be helpful if you can provide them. I want to understand the concepts behind these questions. Thanks in advance!

I'm sorry if this is the wrong forum to be putting this thread in. These are more theory questions, so I thought it more appropriate to put them here than in the homework help. :blushing:
 
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01. Can a star be moving faster than what Doppler effect calculations indicate? This was a discussion question I heard but I'm not sure I understand. Can anyone provide any sort of information about this?
The Doppler shift is a measure of velocity along the line of sight. Velocity perpendicular to the line of sight is extremely difficult to measure (for anything far away), but it has to be considered for the total velocity (Pythag. theorem).

Question 2 - it is an anomaly.
 
  • #3
stardrop said:
01. Can a star be moving faster than what Doppler effect calculations indicate?

mathman is correct that the tangential component's of the star's velocity can't be measured with the spectrum. Because of this, one expects the star to be moving faster than indicated by the Doppler effect.


02. Can someone explain this to me, too? "Hydrogen red line is shifted, but other observations make the star appear to be at rest". It's described as an anamoly, but I don't get it. :cry:

Sorry, this is hard to address without context. There are stars that display redshifted or blue-shifted lines, despite having negligible motion relative to us. This can happen when the star expels gas that creates emission or absorption lines. In that case, the gas could be moving while the star sat stationary. One can also get a redshift from gravitational effects, but in ordinary stars, this effect isn't measurable. Finally, if the redshift is cosmological, then the star could actually be at rest, but appear to moving due to the expansion of the universe.
 
  • #4
Thanks you two so much! Both of these concepts are a lot clearer to me now.
 

1. What is the theory of "Two Questions on Movement"?

The theory of "Two Questions on Movement" was proposed by biologist John H. Long in 2001. It states that there are two fundamental questions that must be answered in order to understand the evolution and mechanics of movement in animals - how do animals generate motion and how do they control that motion?

2. How does the theory of "Two Questions on Movement" apply to different types of animals?

The theory of "Two Questions on Movement" can be applied to all types of animals, from simple organisms like bacteria to complex organisms like humans. It provides a framework for understanding the mechanics and evolution of movement in a wide range of species.

3. What are some key examples of animal movement that can be explained by the theory of "Two Questions on Movement"?

Examples of animal movement that can be explained by the theory of "Two Questions on Movement" include the flapping of bird wings, the swimming of fish, the crawling of insects, and the running of mammals. Each of these movements can be broken down into the two fundamental questions of how motion is generated and how it is controlled.

4. How does the theory of "Two Questions on Movement" contribute to our understanding of evolution?

The theory of "Two Questions on Movement" helps us understand how different types of movement have evolved in different animal species. By studying how animals generate and control motion, we can gain insights into the selective pressures and adaptations that have shaped the diversity of movement in the animal kingdom.

5. How is the theory of "Two Questions on Movement" relevant in the field of biomechanics?

The theory of "Two Questions on Movement" is highly relevant in the field of biomechanics, as it provides a framework for studying the mechanics of movement in animals. By understanding how animals generate and control motion, we can apply this knowledge to design and improve technologies such as prosthetics and robotics.

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