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This may seem a dumb question but I can't visualize this in my mind. If photons are travelling straight then from our eyes or a telescope we should only see part of the star, for example because our eyes or the opening of our telescopes aren't as big as the diameter of that star. If photons are not travelling in a straight line then we should see a blurry image not the actual shape of those objects. Can someone explain what is really happening?

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    $\begingroup$ The stars are far away, so..... $\endgroup$ – user108787 Jun 6 '16 at 11:12
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    $\begingroup$ Individual light rays travel in straight lines, but two lights rays can be at an angle to one another. So the light rays we see from the left of the sun and the light rays we see from the right of the sun are at a slight angle to each other --- exactly the correct angle so that they meet at our eye. $\endgroup$ – gj255 Jun 6 '16 at 11:26
  • $\begingroup$ Each point on the surface of a star is emitting light in all directions. Draw a picture and you will see that we thus receive light from all points on the star which have direct line-of-sight to us. (Caveats: 'surface' is ill-defined, 'line of sight' is ill-defined, 'straight line' is ill-defined.) $\endgroup$ – tfb Jun 6 '16 at 11:27
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This is what you seem to be imagining as happening:

enter image description here

Whereas this is more accurately what's happening:

enter image description here

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The photons are not radiated only in perpendicular (normal) direction from the star surface. In fact, they are radiated into all available directions (180 degrees) from every point on a star surface. The same applies for galaxies as well. For this reason there are photons sent into all directions (including the Earth direction) from each point of a star / galaxy "surface". And so we can see every point of their surface.

enter image description here

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