Ancient Solar Observatory at Fajada Butte


Sun over Fajada Butte at Chaco Canyon

Sunlight and shadows at Fajada Butte served to mark the seasons a thousand years ago.

In the distance is Fajada Butte at Chaco Canyon, New Mexico. It is one of the most famous sites in archaeoastronomy. A thousand years ago, people of the Chaco Culture used it to observe the Sun.

Fajada Butte at Chaco Canyon

At a site now off limits to preserve its integrity, a set of three rocks cast shadows and daggers of sunlight onto a carved spiral petroglyph.

Fajada Butte Sign At Chaco Canyon

People used the position of the projected beams of light as a calendar to mark time through the year. In truth, simply watching the changing position of the rising and setting Sun along the horizon, which was also done here at Chaco Canyon, would have worked just as well.

Fajada Butte Viewpoint at Chaco Canyon

I visited the site today, as part of a trek north through New Mexico, Arizona and into Utah. Chaco Canyon is one of the preeminent sites for archaeoastronomy, demonstrating how well people a thousand years ago (the site was occupied from the mid 800s to the mid 1100s) observed the sky.

For example, a half-day hike takes you to a famous pictograph on a rock face showing a bright star near the crescent Moon, a drawing some have interpreted as being an observation of the supernova of 1054 AD.

Grand Kiva at Chetro Ketl, Chaco Canyon

In its height, thousands of people lived in the pueblos at Chaco Canyon and surrounding area. This is the Great Kiva at the Chetro Ketl pueblo. Wood columns used to hold a wood roof over this structure to make a space for ceremony and ritual.

Iridescent Clouds at Chaco Canyon

I did a little solar observing myself while there. While walking through the maze of rooms at Pueblo Bonito I looked up to see iridescent clouds near the Sun, created by diffraction of sunlight from fine ice crystals.

Public Observatory at Chaco Canyon, New Mexico

In keeping with the site’s astronomical heritage, the Visitor Centre at the Chaco Culture Historical Park has a well-equipped observatory with several top-class telescopes (a 25-inch Obsession Dobsonian among them) and an outdoor theatre for regular stargazing sessions each weekend. This is a world-class Dark Sky Preserve and a World Heritage Site.

– Alan, April 2, 2015 / © 2015 Alan Dyer  / www.amazingsky.com

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