The Great Arc of the Milky Way


Milky Way Panorama (Sept 4, 2013)

The Milky Way sweeps in a great arch of light across the sky.

It’s been a wonderful week for shooting the Milky Way. I had a very clear night on Tuesday but ventured no further than a few hundred feet from home to the harvested canola field next door.

The Milky Way was beautifully placed, as it always is at this time of year, right across the sky from northeast to southwest, with the starclouds of Cygnus passing directly overhead.

The top photo is a panorama of 8 shots, with a camera on a tripod, and each exposure being just 60 seconds with a 14mm lens in portrait orientation. I stitched the segments with PTGui software, rendering the scene with its spherical projection mode which wraps the dome of the sky onto a flat surface in a way that retains the zenith detail as your eye saw it, but greatly distorts the extremities of the scene at either end.

My house is at lower right.

Milky Way over Harvest Field (Sept 4, 2013)

For this image, I used the same lens to take a single view from horizon to well past the zenith. Here the camera was tracking the stars for a set of stacked 5-minute exposures to grab even more detail in the Milky Way.

What stands out as much as the Milky Way are the green fingers of airglow stretching across the sky. These were invisible to the eye but the camera sure picks them up.

Airglow is caused by oxygen atoms, in this case, fluorescing at night as they release some of the energy they absorbed by day. It’s not aurora and generally covers more of the sky, sometimes with a diffuse glow or, as here, with more structured bands that slowly shift over minutes. It varies from night to night and can occur at any latitudes. But usually only cameras pick it up. To the eye, airglow just makes the sky look inexplicably a little less dark than you think it should be on such a clear night.

– Alan, September 7, 2013 / © 2013 Alan Dyer

 

Waterton Lakes by Night


Waterton-Lakes-Panorama-(Aug-29,-2013)

The Milky Way shines over the peaks of Waterton Lakes National Park on a clear summer night.

This was the view last night, August 29, under very clear skies, on the Red Rock Canyon Road in Waterton Lakes National Park, a UN World Heritage Site and a beautiful place for day and nighttime photography.

This is a 7-frame panorama sweeping over about 180° from the southeast at left and into the northwest at right, taking in the autumn constellations rising at left, over to the Milky Way in the south and to the Big Dipper skimming across the northwest horizon at right. Each frame was a 30-second exposure at f/2.2 and ISO 1600.

The green glow at left is from airglow, while the yellow and magenta colours at right are from low-level aurora and from the lights of Pincher Creek and the Crowsnest Pass communities. The bright light at left of centre is from the lights adorning the Prince of Wales Hotel, set amid the general glow of streetlights from the townsite of Waterton Lakes.

The foreground is lit only by starlight.

– Alan, August 30, 2013 / © 2013 Alan Dyer

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

Star Party Panorama


This image depicts a 360° panorama of the field and sky at the Saskatchewan Summer Star Party.

This was my first time shooting a nighttime panorama but it was easy. Just 12 exposures taken at 30° intervals panning around on a levelled tripod, in classic planetarium panorama style. Each exposure was 30 seconds at f/2 and ISO 3200 with the Canon 5D MkII and 24mm lens. It helps to have a high-quality fast lens.

North is at centre, south on either end.

The sky contains some interesting and subtle features that show up well in a wide-angle panorama like this:

– The bright summer Milky Way is setting at left in the southwest while the fainter winter half of the Milky Way is rising opposite, at right in the northeast.

– Jupiter and the Pleiades rise at right just off the Milky Way

– A meteor streaks over the trees at centre

– At centre, to the north, glows a faint yellow and magenta aurora

– The larger green glow left of centre is, I suspect, airglow rather than aurora. It has a striated structure, particularly at right of centre above the trees where it appears as subtle green and red bands arching across the northeast.

The sky this night was dark but did have a brighter than usual background, likely due to the presence of this faint airglow that the camera picks up better than the eye.

Even so, I can see another faint glow:

– A whitish band coming up from the northeast passing through Jupiter and below the Pleaides. That’s the Zodiacal Band, an extension of the brighter Zodiacal Light and caused by sunlight reflecting off cometary dust in the ecliptic plane.

The location of the panorama and star party was the Cypress Hills Interprovincial Park in southwest Saskatchewan, one of the darkest places in southern Canada.

— Alan, August 20, 2012 / © 2012 Alan Dyer