What Does "sr" Stand For in Cosmic Ray Flux Units?

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    Flux Ray Sr Units
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Discussion Overview

The discussion revolves around the meaning of "sr" in the context of cosmic ray flux units, specifically its definition as steradian, a unit of solid angle. Participants explore how to calculate steradians in various scenarios, particularly in outer space, and the implications for cosmic ray detection.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants identify "sr" as steradian, a unit of solid angle, noting that a sphere encompasses 4π steradians.
  • One participant questions how to calculate steradians for a piece of board in outer space, asking for clarification on the reference point.
  • Another participant provides a formula for calculating area in steradians, indicating that it depends on the distance from the observer to the source.
  • There is a discussion about the geometry factor of detectors measuring cosmic rays and how to determine steradians and reference points in outer space.
  • A participant expresses confusion regarding the concept of a "reference point in outer space," suggesting that the detector's aperture defines its solid-angular resolution.

Areas of Agreement / Disagreement

Participants generally agree on the definition of steradian but express differing views on how to apply this concept in the context of cosmic ray detection and the calculation of solid angles in space. The discussion remains unresolved regarding the specifics of reference points and calculations.

Contextual Notes

Limitations include unclear assumptions about the geometry of detectors and the definition of reference points in outer space, which may affect the interpretation of steradian calculations.

toadehep
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the unit of cosmic ray flux is expressed as flux /(m^2.sr.s.GeV), so what does sr stand for?
Thanks.
 
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steradian
 
steradian = unit of solid angle. 4\pi steradians in a sphere.
 
humanino said:
steradian

thanks.
suppose there is a piece of board in outer space, how to calculate its steradian?
what is the reference point?
 
Area(S)=R^2 \int_S\sin\theta~d\theta d\phi

So it depends on your origin (the value of R, since the area is obviously invariant). The same goes for arc length in one less dimension.
 
I voted for blechman in the 2009 PF member physics award. :approve:
 
as to your flux calculation you mentioned: R is the distance from you to the source, so YOU are the reference point. Is that what you meant?
 
humanino said:
I voted for blechman in the 2009 PF member physics award. :approve:

Thanks humanino, I definitely appreciate your support. :biggrin:
 
many experiments are designed to measure the cosmic ray spectrum, including space probes. what confues me most is that, when considering the geometry factor of the
detector, how can we decide the steradan and what is the reference point in outerspace?
 
  • #10
I'm not sure I understand the phrase, "reference point in outerspace". The detector has an aperture that covers a fixed solid-angular resolution in the sky along its line of sight. Maybe I misunderstand your question??
 

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