Tuesday, November 27, 2012


A red sky tonight 
Without moon or stars in sight 
Making my walk bright

What is it that makes the cloudy night sky reddish and the surroundings as bright as if the sky was cloudless with a full moon?


Acolyte of Sagan said...

Assuming that you mean late at night, rather than early evening with the sun low in the sky, the most common cause is simply the clouds catching the artificial light from our towns and cities, etc. and reflecting it back down. This way, the light from a large town can light up the surrounding countryside for many miles. The effect is heightened when the moon is full or near-full as it is effectively back-lighting the clouds and so enhancing the amount of light reaching earth. The colour you see depends on many factors, including the colour of the artificial light hitting the clouds from below, atmospheric dust and gas below and within the clouds absorbing light at different wavelengths and so reflecting only part of the light spectrum back to the viewer(the same reason there are diffferent colours of sunset), and the same above the clouds filtering the sunlight reflected from the moon.
You will probably be experiencing more colourful nights than usual at the moment due to the massive amount of dust blown into the atmosphere by Hurricane Sandy; I'm sure you remember the beautiful colour-schemes bought on by Mt. St. Helens?

Grandmère Mimi said...

So it's light pollution, and last night the moon was full or near so. And the dust. I walk on my street, rather in my street, because we have no sidewalks, and the spaces in between the street lights were quite bright. Well, I hoped the explanation would be more exciting, but now I know. Thanks Acolyte of

Ann said...

Yes -- light pollution. Also keeps one from seeing all the stars when it isn't cloudy -- I am always astounded by the numbers of stars when out on the prairie far from cities. Even here at the coast without much light pollution - the humidity cuts down the view of space.

Grandmère Mimi said...

It's astonishing to the the see the night sky from a place without light pollution. One evening when we were at sea on a cruise, I walked to the stern of the ship where there were no lights, and the sight of the many stars took my breath away.

Acolyte of Sagan said...

You're welcome, Grandmere. I'm sorry it wasn't something more exciting than dust and light pollution. Then again, maybe it's a good thing that the answer was so mundane; exciting doesn't always equal good. There's an ancient Chinese curse that goes "May you live in interesting times"!

Anyway, there's a beautiful moon tonight, with Jupiter chasing it around the sky at the 9 o'clock position, so I'm back off outside to the telescope.

Grandmère Mimi said...

Yes, I've seen the beautiful full moon tonight. At least my walk last night was brightened up by the dust and light pollution. Good thing, because I'd forgotten to wear my reflector vest.

Acolyte of Sagan said...

Come now, with a smile as radiant as yours there's surely no need of a reflective vest.

On a side note, as you tend to walk your dog at night, have you seen those collars that have flashing LED lights on them for high-visibility? There's also a clip-on light unit available that attaches to the dogs existing collar.