Estimating relative distances for star clusters

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Discussion Overview

The discussion revolves around methods for estimating the relative distances of star clusters, focusing on geometric and photometric approaches. Participants explore the implications of assuming star clusters have similar physical sizes and the challenges associated with different measurement techniques.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that if star clusters are of similar physical size, relative distances could be estimated.
  • Another participant proposes that distances can be measured through angular size or apparent brightness.
  • A question is raised about whether geometric distance measurements would yield the same results as photometric measurements based on stellar brightness relations.
  • It is noted that measuring angular diameter has the advantage of being unaffected by external factors, provided the cluster is large enough to be detected above atmospheric seeing.
  • Concerns are expressed regarding photometric measurements, highlighting the need for assumptions and corrections related to interstellar reddening and absorption effects.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the effectiveness of the different methods for measuring distances, and multiple competing views remain regarding the reliability of geometric versus photometric approaches.

Contextual Notes

Limitations include assumptions about the physical size of star clusters, the impact of atmospheric conditions on angular measurements, and the complexities involved in correcting for interstellar effects in photometric measurements.

randa177
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If star clusters were all about the same physics size, how could one estimate their relative distances?
 
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Either by measuring their angular size or apparent brightness.
 
would the distances determined geometrically give the same result as those determined photometrically (using stellar brightness relation)?
 
If they were really the same physical diameter then the advantage of measuring their angular diamter is that it isn't affected by anything else ( assuming it is large enough to be detected above atmospheric seeing)
The problem with measuring brightness is that you have to make assumptions and correct for the absorption and re-emmision from the space in between (Interstellar reddening).
 

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