The Colour of Dark


Colors of the Dark Sky Panorama

What colour is the dark night sky? Depending on conditions, it can be any colour you want.

I shot this 360° panorama last night from my backyard under what looked like a clear and fairly dark, moonless sky. Looks can certainly be deceiving. The camera picked up all kinds of colours the eye couldn’t see.

Let’s review what’s causing the colours:

• To the north just left of  centre the horizon is rimmed with a bright yellow glow from all-night perpetual twilight present around summer solstice at my mid-northern latitude.

• Above that shines a green and magenta band from a low-level aurora just visible to the naked eye.

• Much of the sky is tinted with bands of green from ever-present airglow, caused by oxygen atoms at the top of the atmosphere giving off at night some of the energy they absorbed by day. I had thought the sky would look blue from the perpetual twilight but the airglow seems to overwhelm that.

• Yellow glows around the horizon at left (west) and right (southeast) are from urban light pollution from towns 50 km away.

• Some strands of remaining cloud from a departing thunderstorm add streams of brown as they reflect lights from below.

• Finally, the Milky Way shows up in shades of yellow and pale blue, punctuated here and there by red patches of glowing hydrogen hundreds of light years away.

The only thing missing this night was a display of electric blue noctilucent clouds.

The sources of most of these colours are an anathema to observers of faint deep-sky objects. Aurora, airglow and certainly light pollution just get in the way and hide the light from the distant deep sky.

A word on technique:
I shot this panorama using an 8mm fish-lens to shoot 8 segments at 45° spacings. I used the excellent software PTGui to stitch the segments together, which it did seamlessly and flawlessly. Each segment was an untracked 1 minute exposure at ISO 3200 and f/3.5. The panorama covers 360° horizontally and nearly 180° vertically, from the ground below to the zenith above. It takes in everything except the tripod and me!

– Alan, June 8, 2013 / © Alan Dyer

A Truly Amazing Sky — A New Year’s Gift


Timor Cottage Panorama #3

As we end 2012 and start a new year, I wish everyone a very happy 2013 and leave you with this view of a very amazing sky.

This is a 360° panorama of the Milky Way over Timor Cottage on a very clear night in mid-December in New South Wales, Australia. May all your skies be as wonderful and as inspiring as this in the coming year.

Indeed, we have some potentially remarkable sights to look forward to, with the prospects of two bright comets in 2013: Comet PANSTARRS in March and Comet ISON in November and December.

Let’s hope for more amazing skies in 2013. Keep looking up!

– Alan, December 31, 2012 / © 2012 Alan Dyer

Australian Sky Panorama


Timor Cottage Panorama #1

This is the southern hemisphere sky in a 360° panorama.

From left to right in the sky, you can see:

– in the South: the two Magellanic Clouds, satellite galaxies of the Milky Way

– in the West: the diagonal glow of Zodiacal Light

– in the North: Orion, Jupiter and the Pleiades above the outline of Timor Rock

– in the East: the southern Milky Way just rising

I shot this last night in the early evening, Sunday, December 9, from my observing site in Australia, Timor Cottage at Coonabarabran, NSW. It’s a panorama of 8 images, each a 1 minute untracked exposure with the 10-22mm lens at 10mm. I’m amazed at how well the sections join together, considering the stars are moving from one frame to the next and about 16 minutes separates the beginning and end frames.

– Alan, December 10, 2012 / © 2012 Alan Dyer

 

Milky Way Mosaic


Centre of the Milky Way Panorama (2011)

It’s taken me a few months to get around to the task, but at last! — my mosaic of the Milky Way I shot in Chile back in May.

The panorama is made up of 6 frames, stitched and blended together, extending from Crux, the Southern Cross (at right) to Aquila the eagle (at left) — a sweep of the Milky Way from Acrux to Altair! The mosaic is centred on the core of the Galaxy in Sagittarius and Scorpius.

Panoramas like this allow you to step back a distance and take in the big picture:

— You can see the large-scale structure of the dust clouds and the odd diagonal sweep of many of the clouds cutting across the plane of the Galaxy. I’ve never heard an explanation of why the dust lanes seem to have that structure and direction. I also see a 3D effect, with the nearby dust clouds hanging in front of and obscuring the bright starclouds of the distant inner spirals arms of our Galaxy.

— Also apparent are the extensive dust clouds at left extending from Ophiuchus (at top) down into Aquila, well below the plane of the Galaxy. Most wide-angle shots of the Milky Way I see tend to process out the subtle brown clouds that extend far off the Galactic plane. And they are brown, not black.

— And what really stands out is the band of bright blue stars from Scorpius (at top centre) to the right above the Milky Way through Lupus, Centaurus then down into Crux. This is a section of Gould’s Belt, a ring of hot blue stars around the sky that runs at an angle of about 20° to the Milky Way. This ring of hot, nearby stars surrounds us in our spiral arm and is thought to be only about 65 million years old, likely caused by some disturbance in our spiral arm which set off a wave of star formation close to us.

— And … as my Australian friends will point out, you can see the entire Dark Emu, made of the dust lanes from the Coal Sack in Crux at right (his head and beak), through the curving lanes in Centaurus (his neck), then sweeping up and over the centre of the Galaxy (his body) then down into Scutum and Aquila (his two feet and his tail).

I took this panorama from the Atacama Lodge in north central Chile, using the Canon 5D MkII and Canon 35mm lens. Each of the 6 segments that went into this pan was itself a stack of 4 x 6 minute exposures, plus a fifth exposure through a soft-focus filter, all at f/4 and ISO 800. The camera was on a Kenko SkyMemo tracking platform. I assembled the pan with Photoshop CS5’s Photomerge command. This is actually only half of the full panorama mosaic, which extends for another 5 segments to the right along the Milky Way to Orion, taking in the entire southern portion of the Milky Way. But this is the best bit!

— Alan, Oct 2, 2011 / Image © 2011 Alan Dyer