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

October skies darker than December skies?

  1. Nov 12, 2015 #1


    User Avatar
    Gold Member

    October skies always seem to be very black, whereas December skies seem blue. I don;t know if anyone else has observed this, or whether it's just my imagination.

    I have some hypotheses, but none of them seem satisfactory.

    - Daylight savings ends in late October. So Oct/Nov skies really are darker than Sept. (but that doesn't explain lighter skies in December)
    - It is often rainy in autumn, so the roads reflect vehicle and street lights. And there's (sometimes) snow on the ground in December (though not around here in recent memory).
    - Moon is typically in a different phase for a given time of night? (Don't know)
  2. jcsd
  3. Nov 12, 2015 #2
    We are talking Northern hemisphere of course, and at middle-ish latitudes, but in many parts October is often cloudier than December with more active weather systems around.
    So although October days are longer they are frequently dull due to lots of cloud, (I wouldn't quite compare that dullness with black though).
    Typically in December there are less active weather systems, so less cloudy days, and there can be extended periods of slow moving high pressure systems leading to calm and cloud free skies.
  4. Nov 16, 2015 #3


    User Avatar
    Gold Member

    To my horror, I do not seem to have actually specified that I am referring to night skies.

    Thanks. That actually a pretty plausible hypothesis.
  5. Nov 17, 2015 #4


    User Avatar
    Gold Member

    Is there any directivity that you have noticed - darker/lighter to the south, north east, west.
    Thinking that with the snow on the ground, the Northern Lights, even if you do not see them directly, may reflect back up into the sky.

    Also, what about the Gegenschein,

    Or the Zodiacal light,

    Both due to dust, and since December has you tilted more inline with the solar plane...

    There is also Airglow, to brighten up the night sky,

    Frankly, how seasonal would any of those be?
  6. Nov 18, 2015 #5
    Whoa! Dave. Your eyes must be a lot different than mine. I don't recall ever (and I'm as old as dirt) seeing blue night-time skies in any month. Blue skies are caused by Rayleigh scattering of sunlight--right? There is no sunlight at night--right? Where does the blue come from? Is it subjective?

    I wonder if you would see the same monthly difference if you live somewhere else?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook