Tag: atmospheric optics

Posted on

Ring Around the Moon


Halo Around the Moon (Dec 1, 2014)

Ice crystals create a ring of light around the waxing Moon.

Clouds have moved in this week in New Mexico but the advancing weather system also brought an atmosphere filled with high altitude ice crystals.

Earlier this week they created a lunar halo – a ring around the Moon. If you look closely you’ll see there are two rings. On the left and right sides (east and west) the halo splits into two. This is an effect of two haloes superimposed: the classic 22° halo and what’s called the “circumscribed halo” which changes shape and size depending on the altitude of the Sun or Moon.

In this case, the Moon was 62° up, and the appearance of the circumscribed halo exactly matches what computer simulations predict for this altitude.

See Les Cowley’s wonderful website on Atmospheric Optics and the page on the shape of the circumscribed halo.

The long 30-second exposure brought out the stars in the moonlit sky.

They say such haloes presage poor weather. This week that proved true as clouds and rain moved in.

– Alan, December 4, 2014 / © 2014 Alan Dyer

 

Posted on

Solar Halo in a Cold Blue Sky


Solar Halo and Sundogs (Dec 19, 2013) #2

A solar halo and sundogs surround the Sun on a cold winter day in Alberta.

I’m back home amid the snow and cold. The one celestial treat to such a clear but cold winter day is the appearance of sundogs and solar halos around the cold Sun.

This was this morning, with the low winter Sun above my snow-covered backyard, and the air filled with tiny ice crystals. You can see them as sparkly “stars” in the sky and in the foreground. Those crystals are refracting the sunlight and making the coloured “rainbows” on either side of the Sun called “parhelia” or sundogs. A faint halo encircles the Sun, topped by an upper tangent arc.

You can read more about halos and their origin at Les Cowley’s AtmosphericOptics website.

Solar Halo and Sundogs (Dec 19, 2013) #1

Here’s another view with a wider-angle lens. I’ve punched up the vibrance to bring out the fact that the shadows on such a day are not black or grey but blue, coloured by the intense blue light streaming down from the sky.

With these winter scenes, I wish all my blog fans and followers a very Merry Christmas, happy holidays and a very happy New Year. Clear skies to all in 2014!

 

– Alan, December 19, 2013 / © 2013 Alan Dyer

 

Posted on

The Colours of Iridescent Clouds


Iridescent Clouds at White Sands #3

High clouds shimmer with iridescent colours near the Sun in an unusual display of atmospheric optics.

As I was getting ready to shoot the sunset at White Sands National Monument last evening, December 10, I looked up at the late afternoon Sun and saw it embedded in thin clouds tinted with iridescent colours. My dark sunglasses helped me see the phenomenon by eye, and underexposing the image helped me capture the colours by camera.

The effect is more common than you might think, but being so close to the blinding Sun iridescent clouds often go unnoticed. The almost metallic-looking colours are caused by clouds made of water droplets of such a uniform size they diffract the sunlight and spread the white light into a stunning range of colours.

Iridescent Clouds at White Sands #1

This image frames the scene in portrait mode. I took several images over the few minutes the effect lasted. But the clouds soon moved off or changed structure and the iridescence faded. Despite the Sun shining through similar looking thin clouds the next evening, December 11, I saw no such iridescence.

For more information see Les Cowley’s excellent page at his Atmospheric Optics website.

It’s just another example of the wonderful phenomena of light and colour that the sky can present to the watchful.

– Alan, December 11, 2013 / © 2013 Alan Dyer