Would you see the stars in the day if blue were filtered?

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Discussion Overview

The discussion revolves around the question of whether filtering out blue light from the sky would allow visibility of stars during the day. Participants explore the implications of using optical filters and the nature of scattered light in the atmosphere, considering both theoretical and practical aspects of astronomical observation in daylight.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that using optical filters could enable visibility of stars during the day by removing the brighter blue light scattered in the atmosphere.
  • Another participant argues that while a blue filter might help, it would be limited since scattered light is not exclusively blue but rather a full spectrum weighted towards blue.
  • Some participants note that planets can be viewed during the day without filters, but galaxies are too faint for visibility in daylight.
  • There is a proposal to filter out all colors from violet to green, with mixed opinions on its effectiveness for casual sky gazing versus astronomical observations.
  • Repeated questions about why ground-based astronomers observe at night suggest a belief that nighttime conditions are superior for visibility, although this does not directly address the original question.
  • One participant emphasizes that filtering out colors would also attenuate the light from the stars, potentially negating the benefits of the filter.
  • Another participant references a source discussing the spectrum of blue sky, indicating that the peak is above 500nm and is more of a blue-tinted white.
  • A suggestion is made to experiment with filters while ensuring eye protection from stray light to adapt to lower intensity.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness of optical filters for daytime star visibility, with no consensus reached on the best approach or the potential outcomes of using such filters.

Contextual Notes

Participants acknowledge the complexity of the light spectrum and the limitations of filters, but do not resolve the implications of these factors on visibility.

Vriska
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Would you be able to see stars in the day if the blue of the sky was filtered through an optical filter ? Can I make myself glasses using optical filters that'll enable me to look at the stars even in the day ? If the reason for the fact that we are unable to see stars in the day be the scattered blue light is brighter than the light of the stars , surely filtering out the blue light would enable me to see the stars even during the day .
 
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A blue filter would allow you to see the other scattered wavelengths more clearly. Why do you suppose ground-based astronomers only go out at night?
 
Just one point, while it might possibly help, a filter is of limited use since the scattered light is not blue - if I am not mistaken it as a full spectrum, weighted towards the blue end but not limited to a small range of wavelengths, so you wouldn't be able to cleanly remove the scattered light.

You can view some planets in daylight though (no need for a filter) but galaxies are far too faint and I doubt a filter would be of significant help. Also you do want to observe as much of the spectrum of the galaxy or star as you can.
 
Last edited:
wabbit said:
Just one point, while it might possibly help, a filter is of limited use since the scattered light is not blue - if I am not mistaken it as a full spectrum, weighted towards the blue end but not limited to a small range of wavelengths, so you wouldn't be able to cleanly remove the scattered light.

You can view some planets in daylight though (no need for a filter) but galaxies are far too faint and I doubt a filter would be of significant help. Also you do want to observe as much of the spectrum of the galaxy or star as you can.
What if I filtered all the colours from violet to green ? Yes , you'd want to observe as much of the spectrum of the various stars as possible to make astronomical observations but for casual sky gazing , I think , filtering colours from violet to green won't make a huge difference .
 
I'll ask you again, why do you suppose ground-based astronomers only go out at night?
 
phinds said:
I'll ask you again, why do you suppose ground-based astronomers only go out at night?
I think the answer to this could have gone without saying but apparently not. The answer is because it's much better at night. Except that is not the OP's question.
 
DaveC426913 said:
I think the answer to this could have gone without saying but apparently not. The answer is because it's much better at night. Except that is not the OP's question.
Fair enough.
 
Vriska said:
What if I filtered all the colours from violet to green ? Yes , you'd want to observe as much of the spectrum of the various stars as possible to make astronomical observations but for casual sky gazing , I think , filtering colours from violet to green won't make a huge difference .
It will make a big difference as you are attenuating the light from the stars too.
Looking at https://en.wikipedia.org/wiki/File:Spectrum_of_blue_sky.svg from https://en.wikipedia.org/wiki/Diffuse_sky_radiation, the peak is above 500nm - it's more blue-tinted white that blue really.
But the best thing to do I think is just try looking through some filters and see. You will need to protect your eyes from stray light though, so your pupils adapt to the lower intensity.
 

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