interstellar dust – The Amazing Sky

“Many a night I saw the Pleiads, rising thro’ the mellow shade,

Glitter like a swarm of fireflies tangled in a silver braid.”

– Alfred, Lord Tennyson

These are the famous Seven Sisters, the Pleiades, caught two nights ago in New Mexico skies. This bright star cluster stands out easily to the unaided eye in the winter sky, shining in the shoulder of Taurus.

What the eye does not see is the “silver braid” – the dim dust that surrounds the Pleiades. The stars light the dust, causing it to shine blue near the stars. Farther out, the dust is much dimmer and glows with pale tints of cyan and red.

The dust clouds were once thought to be what was leftover from the formation of the stars, now estimated to have occurred about 100 million years ago. However, current theory suggests that the natal dust of the Pleiads would have long since dispersed.

Instead, the silvery braids of dust that surround the Seven Sisters are just nearby dust clouds in Taurus that the stars are passing through, and illuminating with their hot blue light.

The Pleiades, as familiar as they are – they have been mentioned in ancient texts and myths dating back thousand of years – remain a source of scientific controversy. Astronomers argue over their distance, with different methods providing different results. But the best recent measurement puts them 440 light years away.

Technical notes: This is a stack of 10 x 12 minute exposures at ISO 400 with the Canon 5D MkII camera and 92mm TMB refractor at f/4.4. I shot the images November 16 from near Silver City, New Mexico.

The stars of the Pleiades sit amid a dusty sky in Taurus.

These are the famous Seven Sisters of Greek legend, known as the Pleiades. They are the daughters of Atlas and Pleione, who are also represented by stars in the cluster. Many cultures around the world tell stories about these stars, but in Greek tradition their appearance signalled the summer sailing season in the Mediterranean. The Pleiades first appear at sunset in the eastern evening sky in autumn and put in their last appearance in the western sky in spring.

One story has it they were placed in the sky to recognize their devotion to their father Atlas and his unending labour in holding up the heavens. They are the half-sisters of the Hyades, another nearby cluster of stars in Taurus. Other stories describe the Pleiades as the Seven Doves that carried ambrosia to the infant Zeus.

A seldom-used name now for this cluster is the Atlantides, from the plural form of Atlas, their father. Thus, these sisters gave their name to the Atlantic Ocean, a vast and uncharted sea until the 16th century. The term “atlas,” first used by Mercator for a book of maps, comes not from the Pleiades’ father but from a real-life king in Morocco who supposedly made one of the first celestial globes.

I shot this portrait of the Sisters a few nights ago, stacking a set of five 15-minute exposures with the TMB 92mm refractor and Canon 5D MkII at ISO 800. I processed the image to bring out the faint clouds of dust that pervade the area.

The Pleiades are passing through dust clouds in Taurus and lighting them up. The stars are embedded in dust, lit blue by the light of the hot stars. But even farther out you can see wisps of dust faintly illuminated by the light of the Pleiades.

The stars are thought to be about 100 million years old, quite young as stars go. They formed together in a massive nebula that has long since dissipated, and will travel together for another few hundred million years until the sister stars go their own way around the Galaxy. The stellar family that gave rise to so many legends around the world will be scattered to the stars.