Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The Sun, The Earth, Light.

  1. Mar 17, 2005 #1
    I have a question for you all. I asked my Physics teacher this in school not so long ago. I made an animation of it on a little art thing (which rocks btw, I suggest you all use it for your examples or theoreys)

    http://artpad.art.com/gallery/?idilmbnxbps

    In a nut shell:

    You're on a perfectly flat earth.
    The sun is rising
    What do you see first?
    The planet being illuminated by the light?
    or
    The source of light? (Sun)
    Since light travels faster than anything, as it is an energy, theoretically wouldnt you see it first? But since the object, being the Sun in this case, is not an energy, it does not take time to travel, but instead needs to be bright enough (Think back to light hitting you) or close enough for your eye to recieve. Since it's not close enough for your eyes to recieve it as soon as you look at its heading, you must see the light first, which in turn, is the initial Sun itself.

    My question? Do we see the Sun first? The light first? Or both at the same time.

    EDIT: In my animation, I made a horrid mistake. I blanked out, and forgot the Sun was a star, thus it's a ball of gas, not lava. :rofl:

    My bad. Forgive me?
     
    Last edited: Mar 17, 2005
  2. jcsd
  3. Mar 17, 2005 #2

    selfAdjoint

    User Avatar
    Staff Emeritus
    Gold Member
    Dearly Missed

    You can't see the Sun unless its light reaches you, so you see them both at the same instant!
     
  4. Mar 17, 2005 #3

    Phobos

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    The planet...if your flat Earth has an atmosphere, that is. An atmosphere will refract light from the sun across the planet and to your eyes before the sun rises over the horizon. (consider the twilight of dawn/dusk)

    Like selfAdjoint said, once the sun rises over the horizon, seeing the sun and its direct light is essentially the same thing.
     
  5. Mar 18, 2005 #4
    Light fron the sun takes about 8 minutes to reach the Earth, not 4 minutes. I'd think you'd see the sun first, then the house lighting up; when you see the sun itself, light takes a straight (assuming no atmosphere) path from the sun to your eyes, when you see the house, light goes from the sun to the house, and THEN to your eyes, so the total path of light is longer in this case. Of course this difference would be on the order of a millionths of a second.

    P.S.
    Your animation is mildly amusing.
     
  6. Mar 19, 2005 #5
    i read in your animation that light takes 4 mins to arrive, but i have read also somewhere else that it takes 8 mins and something to reach earth (the ray leaving the sun takes 8 mins and something to arrive to earth)
    any expert can handle it?
     
  7. Mar 19, 2005 #6

    DB

    User Avatar

    the sun takes ~8 mins to reach earth not 4.
     
  8. Mar 19, 2005 #7

    Labguy

    User Avatar
    Science Advisor

    I'm not sure of your question, but the mean light-time to the sun is 499 seconds; 8 minutes, 19 seconds.

    EDIT:
    (1) DB typed faster... :frown:
    (2) With (or even without) an atmosphere, you would see both at the same time as pointed out above.
     
    Last edited: Mar 19, 2005
  9. Mar 19, 2005 #8

    DaveC426913

    User Avatar
    Gold Member

    >You're on a perfectly flat earth.
    The sun is rising
    What do you see first?
    The planet being illuminated by the light?
    or
    The source of light? (Sun)



    This is Simple geometry.

    Pic 1 - Sun is straight overhead.

    The light from the Sun travels 93,000,000 miles in a straight line to reach your eyes. The light from the sun travels 93,000,000 miles to reach the roof of the house next door AND THEN travels a few hundred yards to reach you. The sun travels 93,000,000 miles to reach the roof of the house 100 miles away from you, AND THEN travels AN ADDITIONAL 100 miles to reach you.

    Pic 2 - Sun is rising over the horizon.

    Same thing. While the sunlight is coming from one side, it's light still gets to us first, since it's a straight line. All other light takes a longer path, and thus reaches us later.

    In both cases, the first thing we see is the disc of the Sun, followed by an a circle of light expanding outward from us like spotlight.



    >My question? Do we see the Sun first? The light first? Or both at the same time.

    We do not "see" the Sun. Ever. We can only see the light emitted from the Sun. That is what we mean when we say "we see the Sun".
     
    Last edited: Nov 28, 2006
  10. Mar 19, 2005 #9

    Labguy

    User Avatar
    Science Advisor

    DaveC426913 is more correct, if we are going to measure in billionths of a second.. :yuck:
     
  11. Apr 29, 2005 #10
    Interesting that this question appears on a physics related site, when it is more linguistic or, perhaps philosophical. Dave gave the answer that you do not see the sun ever, you only see the light. Others that you see both at the same time.

    What does it mean to "see". To see is to perceive with the eyes (in this context). Your eyes only see light. Anything you see is only the light it emits or reflections from other light sources. To ask whether you see the sun first or the light it emits is to seperate light emitted from an object from the existence of the object itself. As Dave says, you never see the object with this assumption, whether the object is a table or the sun.

    However, mots of us think that when we see something, we really do see it ie the light is an integral part of the object. We do not seperate what we see as being a table from the table itself. With this standard view, we do not even see the sun and its light at the same time, as this still separates the two. When we see the light, we see the sun. The two are identical.

    Refracted light from the atmosphere was disregarded earlier. How does this fit in with my view? Refraction to me is a from of refelction, like a badly focused mirror. I see myself in a mirror. In a badly cracked mirror I may see myself many times. If the peices are very small I may not be able to recognise myself, but I would expect the little pieces that I see to be part of myself. Is refraction anything more than seeing the sun?

    What is interesting about the sun is that we are seeing a distinct past, whether four or eight minutes ago. People have argued for thousands of years about things like this. Most of us are happy to know that we are seeing the sun even when we know that it is the sun from the past. Would anyone suggest we don't see the stars? It is possible to argue differently, but this is a matter of words.

    I like the philosopher who suggested that words mean what we think they mean. In which case, of course you are right to ask the questions and give the answers you have even though, within my language and mental processes, you are wrong. Truth is, after all, relative.
     
  12. Apr 29, 2005 #11

    Chronos

    User Avatar
    Science Advisor
    Gold Member
    2015 Award

    Oh please, what part of bad science are you referring to? Truth is not relative, nor meaningful in that cowpie argument.
     
  13. Jul 13, 2005 #12

    DaveC426913

    User Avatar
    Gold Member

    While it may appear to smack of philosophy, nothing could be further from the truth.

    The fact that we are seeing only the light emitted by the Sun, and the length of time that light takes to reach us (by straight and/or by crooked path) is directly and concretely relevant to the answer.
     
  14. Jul 13, 2005 #13

    DaveC426913

    User Avatar
    Gold Member

    Well, hundredths of seconds, anyway.

    Light takes 4/100ths of a second to travel the diameter of the Earth - within an order of magnitude of naked-eye visible.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: The Sun, The Earth, Light.
  1. Earth-Sun distance (Replies: 24)

Loading...