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The intensity of the Sun and heat on Earth

  1. Apr 8, 2009 #1
    Hi all.

    Is the explanation for the fact that it is hotter at equator than other places at the Earth that the intensity of the Suns waves are greater at equator, since the number of beams per area is larger (since they are not scattered that much because of the lack of curvature)?

    I hope yoou can enlighten me. Thanks in advance.

    - Niles.
    Last edited: Apr 8, 2009
  2. jcsd
  3. Apr 8, 2009 #2
    Is it perhaps even more correct to say that Poyntings vector only has a component normal to the surface of the Earth at equator, and this the intensity is greatest here?
  4. Apr 8, 2009 #3


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    Look at it in terms of absorption and scatter. If the Sun is directly overhead, the light has less atmosphere to traverse, and arrives at the Earth's surface with the least amount of attenuation. Where can the Sun be directly overhead at local noon? The latitude changes with the seasons and can range from the Tropic of Cancer to the tropic of Capricorn and any latitude in between.
  5. Apr 8, 2009 #4
    How do we know that a beam of light that is absorbed by an atom straight above the equator will also be scattered towards the equator, and not in some other direction?

    And also (this is regarding to seasons), when it is summer in the Northern Hemisphere, it says here (http://ksnn.larc.nasa.gov/k2/s_seasons.html [Broken]) that the light of the Sun hits the Northern Hemisphere more "directly". Do they mean the Poynting vector here or what?
    Last edited by a moderator: May 4, 2017
  6. Apr 9, 2009 #5
    As turbo-1 mentioned, it's basically do to the fact that in winter due to the earth's tilt off the earth-sun orbiting axis (I'm sure that has a less retarded name but I don't feel like looking it up). This tilt means that far from the equator in winter the sun's rays have to traverse more atmosphere to reach the surface and thus lose intensity due to scattering.

    Now, scattering of light is a rather complicated subject but as for your question of direction you might find a discussion of Rayleigh Scattering illuminating (just wiki it) but the short answer is that classically we often treat a light scattering event as a new 'source' if you will and the superposition of all these randomly distributed (random because air molecules are randomly spaced) 'sources' results in a net forward propogation.
  7. Apr 9, 2009 #6
    Thank you for your explanation. It is very good.
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