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In the shadow of the Sun

  1. Oct 21, 2013 #1
    Would a nearby Gamma Ray Burst (GRB) cause the Sun to cast a shadow on Earth if it were to shine from behind it?
     
  2. jcsd
  3. Oct 21, 2013 #2

    UltrafastPED

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    What would you expect for the size of this shadow?
     
  4. Oct 21, 2013 #3
    Hi, Ultra. I guess the shadow would be the size of the Sun, right?
     
  5. Oct 21, 2013 #4

    mfb

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    To a very good approximation, indeed.
    What do you know about the relative size of sun and earth?
     
  6. Oct 21, 2013 #5

    UltrafastPED

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    Yes, but what size is the shadow of the sun on the surface of the earth?
     
  7. Oct 21, 2013 #6

    Chronos

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    As a plasma ball, the sun is a very efficient gamma ray shield. The sun moves across the sky an apparent 60 arc minutes per day. It's apparent diameter is about 30 arc minutes. You should be able to figure out from this about how long the sun could shield us from a GRB [a point source] occurring on a line of sight behind the sun.
     
  8. Oct 21, 2013 #7
    The Sun is bigger but farther, and Chronos said it is 30 arc minutes in diameter.

    30 arc minutes?

    Ok. So what I basically want to know is if the visible luminosity of a GRB is powerful enough to cause the Sun to cast a shadow on Earth. I use GRBs as an example, but I guess a supernova could do it, too, right?
     
  9. Oct 21, 2013 #8

    russ_watters

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    How big is the earth in arc minutes? How much of the earth does that cover...?
    Gamma ray bursts aren't very bright visibly. So it wouldn't be much of a "shadow"
    Yes, and much brighter than a GRB. But still not much of a "shadow".
     
    Last edited: Oct 21, 2013
  10. Oct 21, 2013 #9
    I don't know..:redface:

    I'm trying to picture what the sky would look like if the Sun were to 'eclipse' a GRB or a supernova. It seems that the glare from either of those two events could overwhelm the visible brightness of the Sun by several orders of magnitude, no?

    Are you saying the Sun wouldn't cast any shadow on the Earth with that much light in the background?
     
    Last edited by a moderator: Oct 21, 2013
  11. Oct 21, 2013 #10

    Chronos

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    Radiation from a GRB behind the sun would be enormously diminished.
     
  12. Oct 21, 2013 #11

    russ_watters

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    It's a trick question; That doesn't translate into a size on earth. For this situation, the angular diameter of the sun doesn't matter, only the fact that its real diameter is much larger than earth. All of earth will be in "shadow"
    No. Those events are nowhere close to as bright as the sun (er - perhaps a GRB from within our galaxy would be, but they are rare events and so far are only seen from far away). It depends on distance of course, but a supernova in our galaxy might shine as brightly as Venus.
    Not in the normal sense of the word, no.
    [edit] Tionis, I apologize; I accidentally edited your post instead of replying (for moderators, the buttons are right next to each other). I've tried to restore it to its original form.
     
  13. Oct 22, 2013 #12

    mfb

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    Supernovae are bright, but they won't outshine the sun in visible light. The supernova of 1604 was at a distance of 20 000 light years and reached an apparent magnitude of -2.5. Our sun is 10^10 times brighter than that, in order to get the same magnitude a similar supernova would have to be closer by a factor of 100 000, or .2 light years away. There is no star in this distance, and I think all the stars within 10 light years won't explode as supernova.

    Even if there would be some very bright source, the sun has no solid surface. There would be no shadow similar to a cloud, there would be some large (relative to clouds) transition region.
     
  14. Oct 22, 2013 #13
    OK. I'm convinced. Thanks :-)
     
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