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I Why can I see the entire sun

  1. May 27, 2016 #1
    According to calculations, only 0.000000724654% of sunlight reach earth, and if we can only see an object if the light bounced off the object hits our retina in the eye, then how can we see the entire Sun through any means (telescope, etc.)?
     
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  3. May 27, 2016 #2

    anorlunda

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  4. May 27, 2016 #3

    mfb

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    We can only see roughly half of its surface, the side that faces Earth at any given moment. We only receive a tiny fraction of the whole light emitted, but we receive light from every place of the surface because it is radiated in all directions from all points on the surface.
     
  5. May 27, 2016 #4
  6. May 27, 2016 #5

    davenn

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    true

    .... mfb gave a better response :smile:

    and as he said, you don't see the whole sun ... cuz there is a significant portion facing away from us we see a little over 1/2 of the suns surface
    the same with the moon or even if you were a metre or so away from a spherical light globe


    Dave
     
  7. May 27, 2016 #6
    Exactly because light is emitted from all directions, only a small part reaches Earth. If only such a small portion reaches earth, what we see through our telescopes should only be that small portion of the sun in the sky. However, when observed in the telescope, we can see the entire Sun such that we can observe solar flares at the top of the sun.
     
  8. May 27, 2016 #7
    What I am trying to ask is that only such small portion of sunlight hits the Earth, we shouldn't even be able to see half of the sun facing us. We should only be able to see a small circular area on the Sun's surface
     
  9. May 27, 2016 #8

    davenn

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    Again ... we CANNOT see the entire sun .... reread mfb and my posts
     
  10. May 27, 2016 #9

    davenn

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    why ? there is nothing obstructing your view of the whole surface facing us

    think about my light globe comment, you can see all of the side facing you aye ?

    when you look at the side of a building, you see the whole side if none is obstructed by other buildings trees etc


    Dave
     
  11. May 27, 2016 #10

    Dale

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    We receive a small portion of the light from every portion of the surface (facing us). You are mixing up portions of light vs portions of objects. You don't need to gather all of the light, just some of the light from all of the surface.
     
  12. May 27, 2016 #11
    Sorry I meant to say the half sphere facing us because clearly we don't see behind a sphere. And from the half sphere we can still see top of the sun and especially any solar flares from it. But I am wondering that we shouldn't be able to even see that half entirely since only a small portion of light hits the Earth.
     
  13. May 27, 2016 #12
    That makes sense. Thank you.
     
  14. May 27, 2016 #13

    davenn

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    Thanks Dale ... that worded it better :smile:
     
  15. May 27, 2016 #14

    phinds

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    The sun is not reflecting any light at all, it is emitting light.

    Is there a light bulb near where you are? Look at it. Can you see it? Do you think all of its light is coming directly to your eye?
     
  16. May 27, 2016 #15
    Only a portion of the light from the sun reaches us, but what does reach us carries most if not all of the information about the visible area of the sun. What we "lose" is the intensity, not the information.
     
  17. May 28, 2016 #16

    PeroK

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    I guess you are imagining something like this:

    images?q=tbn:ANd9GcTKNBBnn8VJyyTszhq78Zb8Ip_D5DuDp26knGn-CqBayK6W8UAU.jpg
    From which you have inferred that each point of the Sun's surface emits light only in the direction normal to the surface. As explained above, that is not the case.
     
  18. May 28, 2016 #17

    mfb

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    @PeroK: Images stick much more than words, a wrong image easily sticks and does the opposite of what you wanted.

    Here is a graphical explanation of my previous post. Every point on the surface radiates in all directions, only a tiny fraction of that reaches our telescopes/eyes - but a tiny fraction from everywhere does. Distances and sizes not to scale ;).

    sun.png

    The fraction reaching a telescope or an eye is even smaller by many orders of magnitude.
     
  19. May 28, 2016 #18

    anorlunda

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    I interpreted the OP as meaning that he wanted to see 100% of the light emitted by the sun. Therefore, my reply about a Dyson Sphere was only partially tongue in cheek.

    @FQVBSina , it sounds like you are somehow confusing the intensity of the light we see from the sun with the fraction of the sun's surface that we see. You must decouple those things in your mind. If I look at a light bulb directly or wearing sunglasses, the percentage of the bulb's light hitting my eyes is very different, but the fraction of the bulb's surface that I see is the same.
     
  20. May 28, 2016 #19

    Janus

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    On a somewhat related note, It was once considered possible that Pluto was larger than it appeared to be. Unlike the Sun, which emits an equal amount of light is all directions from each point of its surface, Pluto is seen by reflected light. The argument was that if Pluto's surface was very icy and smooth, much of the Sun's light hitting it would not be reflected back in a direction where we would see it, and what we were seeing was just a highlight on that smooth surface, making it look smaller than it really was. Of course, this turned out to not be the case (in fact, Pluto turned out to smaller than original estimates when it was discovered that light we thought was just Pluto turned out to being coming from Pluto and Charon combined)
     
  21. May 28, 2016 #20

    sophiecentaur

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    If you were trying to photograph the Earth, it's clear that a fisheye lens facing downwards from a plane would only grab information out as far as its horizon. The higher you went, the more your camera could grab. But there is a limit because lines form the camera will always diverge and you will never quite get the whole hemisphere. It's the same for the Sun. If you wanted to photograph the whole of the spherical surface you would need more than just two photos (from opposite sides). There will be a finite size ring which both photos would miss. Also, of course, the bits round the edge would be very distorted. Depending on how much distortion you could accept, you would need several shots, each one overlapping its neighbours. At least three would be needed just to get the whole of the equatorial region in shot. For the whole surface and to eliminate distortion, you would need, say, pictures separated by less than 60 degrees of latitude and longitude. That would require at least 12 separate pictures. Easy enough for the Earth but a major project for the Sun. Hardly worth while for the Sun because the surface is boiling away an permanently on the move.
     
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