airglow – The Amazing Sky

August 13, 2016August 13, 2016

The Perseids Perform

Radiant of the Perseid Meteor Shower (2016)

It was a great night for shooting meteors as the annual Perseids put on a show.

For the Perseid meteor shower I went to one of the darkest sites in Canada, Grasslands National Park in southern Saskatchewan, a dark sky preserve and home to several rare species requiring dark nights to flourish – similar to astronomers!

This year a boost in activity was predicted and the predictions seemed to hold true. The lead image records 33 meteors in a series of stacked 30-second exposures taken over an hour.

It shows only one area of sky, looking east toward the radiant point in the constellation Perseus – thus the name of the shower.

Extrapolating the count to the whole sky, I think it’s safe to say there would have been 100 or more meteors an hour zipping about, not bad for my latitude of 49° North.

Lone Perseid in the Moonlight — A lone Perseid meteor streaking down below the radiant point in Perseus, with the sky and landscape lit by the waxing gibbous Moon, August 11, 2016. Perseus is rising in the northeast, Andromeda is at right, with the Andromeda Galaxy right of centre. Cassiopeia is at top. Taken from the 70 Mile Butte trailhead in Grasslands National Park, Saskatchewan.

The early part of the evening was lit by moonlight, which lent itself to some nice nightscapes scenes but fewer meteors.

Perseid Meteor Shower Looking North (2016) — The 2016 Perseid meteor shower, in a view looking north to the Big Dipper and with the radiant point in Perseus at upper right, the point where the meteors appear to be streaking from. This is a stack of 10 frames, shot over one hour from 1:38 a.m. to 2:37 a.m. CST. The camera was on the Star Adventurer tracker so all the sky frames aligned. The ground is from a stack of four frames, mean combined to smooth noise, and taken with the tracker motor off to minimize ground blurring, and taken at the start of the sequence. All exposures 40 seconds at f/3.2 with the 16-35mm lens and Canon 6D at ISO 6400.

But once the Moon set and the sky darkened the show really began. Competing with the meteors was some dim aurora, but also the brightest display of airglow I have even seen.

It was bright enough to be visible to the eye as grey bands, unusual. Airglow is normally sub-visual.

But the camera revealed the airglow bands as green, red, and yellow, from fluorescing oxygen and sodium atoms. The bands slowly rippled across the sky from south to north.

Airglow is something you can see only from dark sites. It is one of the wonders of the night sky, that can make a dark sky not dark!

TECHNICAL:

The lead image is stack of 31 frames containing meteors (two frames had 2 meteors), shot from 1:13 am to 2:08 a.m. CST, so over 55 minutes. The camera was not tracking the sky but was on a fixed tripod. I choose one frame with the best visibility of the airglow as the base layer. For every other meteor layer, I used Free Transform to rotate each frame around a point far off frame at upper left, close to where the celestial pole would be and then nudged each frame to bring the stars into close alignment with the base layer, especially near the meteor being layered in.

This placed each meteor in its correct position in the sky in relation to the stars, essential for showing the effect of the radiant point accurately.

Each layer above the base sky layer is masked to show just the meteor and is blended with Lighten mode. If I had not manually aligned the sky for each frame, the meteors would have ended up positioned where they appeared in relation to the ground but the radiant point would have been smeared — the meteors would have been in the wrong place.

Unfortunately, it’s what I see in a lot of composited meteor shower shots.

It would have been much easier if I had had this camera on a tracker so all frames would have been aligned coming out of the camera. But the other camera was on the tracker! It took the other composite image, the one looking north.

The ground is a mean combined stack of 4 frames to smooth noise in the ground. Each frame is 30 seconds at f/2 with the wonderful Sigma 20mm Art lens and Nikon D750 at ISO 5000. The waxing Moon had set by the time this sequence started, leaving the sky dark and the airglow much more visible.

May 29, 2016May 29, 2016

Glows and Streaks in the Spring Sky

The Spring Sky over the Pioneer Farmstead

How many sources of skyglow can you pick out here?

There are at least five:

• the Milky Way (at left),

• green airglow (below the Milky Way),

• all too prevalent light pollution (especially reflected off the clouds coming in from the west at right),

• lingering blue twilight across the north (at left and right), common in May and June from my northern latitude,

• and even a touch of aurora right at the northern horizon at far left.

In this scene from May 28, the Milky Way arches over an abandoned pioneer farmstead from the 1930s and 40s near my home in southern Alberta.

Mars (very bright and in some clouds) and Saturn shine at lower centre, while Jupiter is the bright object in clouds at right just above the old house.

Arcturus is the brightest star here at upper right of centre, made more obvious here by shining through the clouds. The Big Dipper, distorted by the map projection used in the this panorama, is at upper right.

Technical: This is a 360° horizon to zenith panorama taken with the iPano motorized panning unit, using the 24mm lens at f/2.8 and Nikon D750 at ISO 6400, for a stitch of 28 panels, in 4 tiers of 7 segments each. Stitched with PTGui. South is at centre, north to either end. The original is 25,700 x 7,700 pixels.

Just after I shot the panorama I captured the International Space Station passing directly overhead in one of several passes this night.

ISS Pass #2 (May 28/29, 2016) — The second Space Station pass of May 28/29, 2016, at 1:40 a.m., with cloud moving in adding the glows to all the stars. Taken with the 8mm fish-eye lens from home. The Big Dipper is high in the west at right. Mars is bright at bottom, to the south. Several other satellites are in the sky as well. This is a stack of 3 exposures, each 2.5-minutes with the camera on the Star Adventurer tracker.

At this time of year the ISS is lit all night by the Sun that never sets for the astronauts. We see the ISS cross the sky not once but several times in a night at 90-minute intervals.

While the sky near solstice is never dark at my latitude, it does have its compensations and attractions.

March 15, 2015

The Ghostly Glows of a Truly Dark Sky

A truly dark sky isn’t dark. It is filled with glows both subtle and spectacular.

Last night, March 10, I drove up into the heart of the Gila Wilderness in southern New Mexico, to a viewpoint at 7,900 feet in altitude. I was in search of the darkest skies in the area. I found them! There was not a light in sight.

The featured image is a 180° panorama showing:

– the Zodiacal Light (at right in the west)
– the Milky Way (up from the centre, in the south, to the upper right)
– the Zodiacal Band (faintly visible running from right to left across the frame at top)
– the Gegenschein (a brightening of the Zodiacal Band at left of frame, in the east in Leo)

The Zodiacal Light, Zodiacal Band, and the Gegenschein are all part of the same phenomenon, glows along the ecliptic path – the plane of the solar system – caused by sunlight reflecting off cometary and meteoric dust in the inner solar system.

The Gegenschein, or “counterglow,” can be seen with the naked eye as a large and diffuse brightening of the sky at the spot exactly opposite the Sun. It is caused by sunlight reflecting directly back from comet dust, the scattering effect greatest at the point opposite the Sun.

The Zodiacal Light requires reasonably dark skies to see, but the fainter Zodiacal Band and Gegenschein require very dark skies.

Now is prime season for all of them, with the Moon out of the way, and the Zodiacal Light angled up high in the western as twilight ends. In March, the Gegenschein is now located in a relatively blank area of sky in southern Leo.

The Milky Way is much more obvious. Along the northern winter Milky Way here you can see dark lanes of interstellar dust, particularly in Taurus above and to the right of Orion. Red nebulas of glowing gas also lie along the Milky Way, such as Barnard’s Loop around Orion.

– Orion is at centre, in the south, with Canis Major and the bright star Sirius below and to the left of Orion. Canopus is just setting on the southern horizon at centre. It barely clears the horizon from 32° North latitude.

– To the right of Orion is Taurus and the Pleiades star cluster at the top of the Zodiacal Light pyramid.

– Venus is the bright object in the Zodiacal Light at right, in the west, while fainter Mars is below Venus.

– At far right, in the northwest, is the Andromeda Galaxy, M31.

– Jupiter is the bright object at upper left, in the east, in the Zodiacal Band, and near the Beehive star cluster.

– The Zodiacal Light, Band and Gegenschein all lie along the ecliptic, as do Mars, Venus and Jupiter.

Glows on the horizon are from distant SIlver City, Las Cruces and El Paso. The brighter sky at right is from the last vestiges of evening twilight. Some green and red airglow bands also permeate the sky.

I shot this March 10, 2015 from the summit of Highway 15, The Trail of the Mountain Spirits, that twists and winds through the Gila Wilderness.

It was a stunning night, clear, calm, and silent. Just me under the ghostly glows of a truly dark sky.

NOTE: I first published this March 11 but had to republish this blog March 15 after WordPress deleted the original post in a software bug. Thanks WordPress!

November 23, 2014

Stargazing under the Milky Way

What a wonderful night for stargazing under the Milky Way and amid the rock formations of southern New Mexico.

This was the scene last night, November 22, at a monthly stargazing session hosted by the City of Rocks State Park and the local Silver City Astronomy Club. You couldn’t ask for a better night … and site.

The Milky Way swept overhead, from Sagittarius setting in the west at left, to Taurus rising in the east at right. The faint glow of Zodiacal Light sweeps up from the last glow of western twilight to the left. Some faint green bands of airglow that only the camera can capture are also visible near the horizon.

Matt is doing a laser tour, following which the group convened to the beautiful roll-off roof observatory that houses a Meade 14-inch telescope. It was a fine evening indeed.

Technical notes:

The panorama, which spans about 300° (I cropped the edges a little from the full 360°) consists of 8 segments, shot at 45° spacings, with a 15mm full-frame fish-eye lens at f/2.8, for 1 minute untracked exposures for each frame at ISO 800 with the Canon 6D. I stitched the segments in PTGui software, but processed them in Adobe Camera Raw and Photoshop.

September 26, 2014

Autumn Stars Rising over Dinosaur Park

The autumn constellations rise into a colourful sky at Dinosaur Provincial Park, Alberta.

Last night the sky started out beautifully clear but as it got darker it was apparent even to the eye that the sky wasn’t really dark, despite the lack of any Moon.

The camera captured the culprit – extensive green airglow, to the east at right. A faint aurora also kicked up to the north, at left, adding a red glow. Light pollution from gas plants nearby and from Brooks 50 km away added yellow to the sky scattered off haze and incoming cloud.

The sky colours added to the scene of the autumn constellations of Cassiopeia, Andromeda, Perseus and Pegasus rising in the east. The Andromeda Galaxy is at centre. The Pleiades is (are?) just rising over the hill.

This is a composite of five stacked and tracked exposures for the sky (with the camera on the Star Adventurer tracking mount) and four stacked but untracked exposures I took at the end of the sequence for the sharp ground (I just turned the tracker motor off for these).

July 27, 2014July 27, 2014

Panoramas of the Summer Milky Way

The Milky Way spans the sky on a summer night at a dark-sky star party.

What a fabulous weekend! For the last few nights I’ve enjoyed the skies and hospitality of the Table Mountain Star Party in northern Washington state, near Oroville, just south of the Canada-US border. The site is the Eden Valley Guest Ranch, under superbly dark skies.

About 300 people, mostly from Washington, enjoyed getting under the Milky Way.

As I wandered around the telescope field I heard all kinds of excited comments in the dark: “Wow, look at that!” “Hey, take a look at the Swan Nebula!” “Want to see the Veil Nebula?”

I was impressed with the great mix of ages and demographics at the TMSP – it wasn’t just “old timers.” There were young families, couples, teens, even a pair of grannies pulled in for a look at the starry sky!

The summer Milky Way arches across the sky in these 360-degree “pans.”

But the other main feature is the green fingers of airglow rising out of the east (at left in the circular image above). Only the camera picked these up – the sky looked very dark to the eye. There’s even a faint magenta glow on the northern horizon (at top in the circular image) from aurora.

Both images capture the entire sky, in a panorama set I took using a 14mm Rokinon lens, shooting vertically for 8 segments at 45° spacings. Each frame was a 45-second exposure at f/2.8 and ISO 6400, on a standard tripod, no tracking.

I used PTGui software to stitch and blend the images, then Photoshop CC 2014 to finish them off.

The top image uses “equirectangular” projection; the bottom image “stereographic” projection for a fish-eye effect. Both take in the entire sky from horizon to horizon, plus a lot of ground, filled with red-lighted and happy observers.

December 8, 2013December 10, 2013

Skyglows Galore in the New Mexico Dawn

A mix of sky glows fills the pre-dawn sky in New Mexico.

To the eye the sky looked dark, marred only by some high haze drifting through. But the camera reveals a sky filled with an amazing wealth of colourful glows.

I took this 360° panorama in the pre-dawn hours (4:45 a.m.) this morning (December 8) from the Painted Pony Resort in southwest New Mexico. It reveals a swath of green airglow to the north, the zodiacal light, and the Milky Way. At northern latitudes there was bright aurora visible last night. We might have seen some sign of it here in New Mexico in the form of increased airglow activity.

The panorama takes in, from left to right:
• Arcturus, shining like an ornament on the treetop
• the zodiacal light rising up from the east
• red Mars embedded in the zodiacal light below Leo
• the Milky Way from Puppis and Canis Major at left arching up and across the sky down into Perseus at right
• Sirius the brightest star
• Orion setting over the main house
• Jupiter, the bright object at top centre in Gemini
• Aldebaran and the Pleiades setting right of the main house in Taurus
• Polaris over the smaller house at right
• the Big Dipper at upper right pointing down to Polaris
• a green glow along the northern horizon above the smaller house that is likely intense airglow.
• green and red bands throughout the sky are airglow, caused by atmospheric molecules flourescing at night
• bands of high cloud also permeate the sky adding natural glows around the stars.

I stitched this panorama using PTGui software, from 6 segments, all tracked, taken with the 14mm Rokinon lens at f/2.8 for 2.5 minutes each and with the Canon 5D MkII at ISO 1600.

As a postscript — this is blog post #401 from me.

September 7, 2013

The Great Arc of the Milky Way

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.

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.

August 30, 2013August 30, 2013

Waterton Lakes by Night

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.

June 8, 2013June 9, 2013

The Colour of Dark

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!

August 20, 2012August 21, 2012

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.