In optics experiments we assume that the sun rays are parallel

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Discussion Overview

The discussion revolves around the assumption in optics experiments that sunlight rays are parallel, and the apparent divergence of sunlight observed when it passes through clouds. Participants explore the reasons behind this discrepancy and engage in thought experiments to illustrate their points.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants note that while optics experiments assume parallel sun rays, the sunlight appears to diverge when viewed through clouds, prompting questions about the reasons for this observation.
  • One participant suggests a thought experiment involving drawing nearly parallel lines on paper to illustrate how perspective can affect the perception of angles and convergence.
  • Another participant emphasizes that if lines are exactly parallel, they will never meet, but if they have a small angle, they can appear to converge, drawing a parallel to how light rays from the sun are not perfectly parallel.
  • Some participants challenge the observation of divergence, with one stating they do not perceive any divergence and questioning the interpretation of sunlight angles as divergence.
  • A participant connects the discussion to geometric perspective effects, likening the appearance of diverging rays to how railway tracks or roads seem to converge at a distance.

Areas of Agreement / Disagreement

Participants express differing views on the observation of sunlight divergence, with some agreeing on the perspective explanation while others contest the existence of divergence. The discussion remains unresolved regarding the perception of sunlight behavior.

Contextual Notes

Participants reference geometric perspective effects and the conditions under which light rays are considered parallel, but there are unresolved assumptions about the nature of sunlight and the interpretation of visual observations.

ritwik06
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Even though in optics experiments we assume that the sun rays are parallel, we can clearly see that the sunlight seems to diverge from the sun when coming through the clouds. Whats the reason of this discrepancy?
 
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Take a sheet of paper and draw two straight lines across it that are nearly parallel, but meet near one edge of the paper. Now hold the opposite edge of the paper near your eye, and tilt the paper so you're looking across the width of the paper towards the point where the lines meet. What does the angle between the lines look like now?

Or take a pair of chopsticks (or something similar), hold them together at one end with a small angle between them, and then look along the sticks from the "open" end. (Be careful not to poke your eyes out! )
 
jtbell said:
Take a sheet of paper and draw two straight lines across it that are nearly parallel, but meet near one edge of the paper. Now hold the opposite edge of the paper near your eye, and tilt the paper so you're looking across the width of the paper towards the point where the lines meet. What does the angle between the lines look like now?

Or take a pair of chopsticks (or something similar), hold them together at one end with a small angle between them, and then look along the sticks from the "open" end. (Be careful not to poke your eyes out! )

Well, if the lines are nearly parallel how will they meet ? :eek:
 
If the lines are exactly parallel, they never meet, of course. If they are not exactly parallel, that is, with a small angle between them, then they can meet.

Light rays from the sun are clearly not exactly parallel, because they do meet at the sun!

Have you tried my little experiment yet?

Also note that even lines that are exactly parallel can appear to meet "at infinity" because of geometric perspective effects. Have you ever looked down a long straight road or railroad track that extends to the horizon on a flat plain? The sides of the road or the rails of the track appear to meet at the horizon.
 
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ritwik06 said:
Even though in optics experiments we assume that the sun rays are parallel, we can clearly see that the sunlight seems to diverge from the sun when coming through the clouds. Whats the reason of this discrepancy?

Perhaps you "clearly see that the sunlight seems to diverge" , I do not. What is this divergence you claim to observe. keep in mind that the angle at which the sun's rays come through the clouds is determined by the season and time of day, but that is not the same as divergence of the rays. I do not observe any divergence.
 
Integral, ritwik is referring to something like this: http://www.vagabond-ireland.com/silver_lining.jpg

The answer, ritwik, is in jtbell's post, and it's the same reason that railway tracks or the sides of a straight road appear to converge at a distant point (or diverge as they approach you) - perspective!

PS: For some reason, I missed the last part of jtb's second post, and the similarity of content is purely coincidental!
 
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jtbell said:
If the lines are exactly parallel, they never meet, of course. If they are not exactly parallel, that is, with a small angle between them, then they can meet.

Light rays from the sun are clearly not exactly parallel, because they do meet at the sun!

Have you tried my little experiment yet?

Also note that even lines that are exactly parallel can appear to meet "at infinity" because of geometric perspective effects. Have you ever looked down a long straight road or railroad track that extends to the horizon on a flat plain? The sides of the road or the rails of the track appear to meet at the horizon.

Oh yes, I have understood now. I did the activity with the paper, now what should I do further?
 

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