Calculating the distance between the clusters

  • Context: Undergrad 
  • Thread starter Thread starter CaptCoonoor
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Discussion Overview

The discussion revolves around calculating the distance to star cluster 1 based on its measured flux compared to a nearby blue star. Participants are exploring the relationship between flux and distance, particularly how flux decreases with distance in an astrophysical context.

Discussion Character

  • Exploratory, Mathematical reasoning, Homework-related

Main Points Raised

  • One participant provides the flux of a blue star and a star in cluster 1, posing a question about how to calculate the distance to the cluster.
  • Another participant notes that flux decreases proportional to \(\frac{1}{r^2}\), suggesting this is a key concept for the calculation.
  • Further requests for clarification indicate that some participants seek more guidance on applying the concept of flux decrease to the problem.
  • A hypothetical scenario involving a light bulb is presented to illustrate the concept of flux decrease with distance, prompting further exploration of the ratio of distances based on flux values.
  • Participants discuss the application of the light bulb analogy to the stars, focusing on the ratio of flux decrease and its implications for calculating distances.

Areas of Agreement / Disagreement

There is no consensus yet; participants are still exploring the problem and seeking clarification on the application of the concepts involved.

Contextual Notes

The discussion relies on the assumption that participants understand the inverse square law related to flux and distance, but specific mathematical steps and definitions are not fully resolved.

CaptCoonoor
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Blue star 1 is 1.36 parsecs from you, and has a measured flux of 9.6×10−9Wm−2.

The similar colour star in star cluster 1 has a measured flux of 9.5×10−21Wm−2.

How far away (in Mega-parsecs) is star cluster 1?

Can anyone tell me how to start off? I'll do the rest
 
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The flux falls off proportional to [itex]\frac{1}{r^2}[/itex]. Is this enough of a hint?
 
a little bit more please
 
Suppose I said the flux from a light bulb 1 meter away is [itex]I_0[/itex] Then I move the light bulb until the flux is [itex]\frac{I_0}{4}[/itex]. How far away is the light bulb now?
 
phyzguy said:
Suppose I said the flux from a light bulb 1 meter away is [itex]I_0[/itex] Then I move the light bulb until the flux is [itex]\frac{I_0}{4}[/itex]. How far away is the light bulb now?
2 m?
 
OK, good. Now apply this same logic to the stars. By what ratio has the flux decreased? So what is the ratio of the distances?
 

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