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I've many times heard expressions such "cold, starry nights". It's apparently poetic to describe star-lit night skies as being "cold".

Is this based on reality in some way? Is there something about cold weather which would make the stars more visible from Earth?

I've been taking many nightly walks and, maybe, I'd say that the stars seem to be more visible when it's cold/winter. But I'm far from sure about that; it's useless as "evidence". I don't really see why this would be. Seems like it would have more to do with how cloudy it is.

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  • $\begingroup$ If you can locate an infrared thermometer (point it at something and it reports the thing's temperature) that reads down to low temperatures, you can point it at the sky on a very cloudy night and again on a very clear night, and you'll see a big difference. Roughly speaking the clear sky will read surprisingly cold, since in some thermal IR wavelengths it's fairly transparent and you're seeing the "cold of space" where as clouds will be much more opaque and you'll read something like their temperature. $\endgroup$
    – uhoh
    Nov 28, 2020 at 0:56

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Yes. Clear skies allow the Earth to cool more effectively at night. If there are clouds, these re-radiate some portion of the infrared flux from the Earth back towards the ground, keeping it warmer.

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To add to Rob Jeffries answer, there are a couple of other factors.

  1. Meteorology: when a cold front passes over a location, relatively warm cloudy conditions are followed by rain, and the cooler clearer skies. It may also be windier, which can lead to the brighter stars twinking more, which probably emphaises the clearness. It is also thought that the preceeding rain helps wash out dust from the atmosphere. This is the case in the mid latitude western Europe. I'm not sure about other parts of the world.

  2. Seasonality: winter nights are longer than summer nights. This is particularly noticeable at mid to higher latitudes. Longer nights mean more chance to see the stars, and it's colder in the winter. In fact, at mid and high latitudes, it may never get completely dark in the summer. Even if it does, hotter days may mean there is more dust to be swept up into the atmosphere, reducing clarity.

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    $\begingroup$ Also, the dew point is lower for colder temperatures, so the atmosphere can hold less humidity. This probably doesn't matter much for observing in dry climates. $\endgroup$
    – Connor Garcia ♦
    Nov 27, 2020 at 18:38
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I live far out in the country under very dark skies. I walk my dogs every night after midnight. Summer temps in the 90's. Winter temps get down to -40 deg. I have been doing this for over twenty years. As an amateur astronomer I do pay close attention to the sky whenever I am outside at night.

No romance in the seasons. If anything the skies are the darkest in the spring when the Milky Way is below the horizon. The rare clearest observing nights can occur any time during the year.

As science is devoted to finding the truth I suggest we make the poets sit outside for a few hours every winter night. We might get more references to hemorrhoids than romance in their prose, but at least we will know they are being honest. :)

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