Why are nights the darkest in Alaska between...?

Discussion in 'Earth Science' started by pluto2, Jun 12, 2008.

  1. pluto2 Registered Senior Member

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    Why are nights the darkest in Alaska between December-March? What makes nights in some time darker than in the rest of the year?
     
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  3. spidergoat Valued Senior Member

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    The Earth tilts like this in addition to simply rotating around it's axis:

    Please Register or Log in to view the hidden image!

     
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  5. cosmictraveler Be kind to yourself always. Valued Senior Member

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    I would think there would be MORE light during those months for more light reaches that area during that season than any other.
     
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  7. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Spidergoats animation in post 2 can miss lead. That is the view from the sun. There is very little and extremely slow real tilt to the Earth axis of rotation. The seasons and the "tilt" shown in Post 2 are due to fact that the axis of rotation is fixed in space but not perpendicular to the plane the Earth is moving in around the sun.
     
  8. D H Some other guy Valued Senior Member

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    Billy is absolutely correct. Not only can that animation in post 2 be misleading, it obviously is misleading because it misled spidergoat to claim
    So, what is this image? Imagine taking one picture per synodic day of the Earth as seen from the Sun with the Earth centered in each picture. String those pictures together as an animated GIF and tada!, the image in post 2 is what would result. Several things are missing from the picture sequence. The Earth's orbital motion is obscured by the fact that the pictures are centered on the Earth. The Earth's rotation motion is obscured by the fact the the pictures are taken once per synodic day. It is a nice picture if one knows what is being shown. It is also very misleading.

    The Earth's axis dues undergo nutation and precession, but for the most part are very slow processes. The largest in magnitude traces out a cone with half-angle 23.5 degrees every 25,772 years (precession). Nutation involves a much shorter term variations (the largest contributor has an 18.6 year period) but is much, much smaller in magnitude (tens of arcseconds) than precession (tens of degrees). There are some fast nutation terms, but these are extremely tiny.
     
  9. Spud Emperor solanaceous common tater Registered Senior Member

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    I think it's because the sun is at a greater angle from the horizon which lets less light to 'spill' around the horizon. By this I mean the sun goes further behind the Earth in these months.

    Also the darkest nights have no moon and/or heavy cloud cover.
     
  10. D H Some other guy Valued Senior Member

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    This is exactly wrong. Unless you live in the tropics, you have some kind of winter where you live. The sunlit portion of the day is shorter during the winter than it is during the summer. If you live in the northern hemisphere, you are just about to experience the day with the longest period of sunlight. The extremes in length of day versus length of night grows as one moves toward the poles. Winter days are extremely short or even non-existent in the far north; summer nights are equally short or even non-existent.
     
  11. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    to D H:

    Thanks for the help. Sometimes I think I am the only warrier against NONSENSE very active here, but your talents are more and better reserved for mathematic etc. that I can not do, only admire.
     
  12. pluto2 Registered Senior Member

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    Ok, i get it. Thank for your explanation guys.
     

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