Why is infrared called the heat signature?

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Discussion Overview

The discussion revolves around the terminology of infrared radiation as a "heat signature," exploring the relationship between infrared radiation, temperature, and energy transfer. It touches on concepts from physics and thermodynamics, particularly in the context of blackbody radiation and molecular interactions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants inquire about the relationship between infrared radiation and the term "heat signature," suggesting that searching for related terms may yield insights.
  • One participant notes that the energy of infrared photons corresponds to rovibrational transitions in molecules, making it effective for transferring energy as heat.
  • Another participant mentions that objects at typical temperatures predominantly emit infrared radiation, indicating that measuring this emission can serve as a temperature indicator.
  • It is pointed out that very hot objects, such as stars, emit radiation primarily in the visible spectrum but still produce significant infrared radiation, with an estimated 40% from the sun.

Areas of Agreement / Disagreement

Participants express various viewpoints regarding the relationship between infrared radiation and heat signatures, but there is no consensus on a singular explanation or understanding of the terminology.

Contextual Notes

The discussion does not resolve the underlying assumptions about the definitions of "heat signature" and "infrared radiation," nor does it clarify the extent to which these concepts are interrelated.

justinpod
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Why exactly is infrared radiation called the heat signature?
 
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justinpod said:
Why exactly is infrared radiation called the heat signature?

Welcome to the PF.

When you do some searching on those two terms on google and on wikipedia.org, what kind of relationships do you find? If you add the search term "blackbody radiation", do you get more focused hits?
 
The energy of a photon in the infrared spectrum corresponds to many of the rovibrational transitions in abundant molecules, so it is very effective at being transferred to internal energy, or heat.
 
At temperatures normally held by many objects, the radiation is predominately in the infrared. So measuring the infrared emission is an indicator of temperature.

For very hot objects like stars, much of the radiation is in the visible, though there is still a lot of infrared emitted (of order 40% or so in the case of our sun, iirc).
 

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