Proton Arc – The Amazing Sky

March 4, 2017March 4, 2017

Auroras from Alberta

Aurora Self-Portrait (March 2 2017)

The solar winds blew some fine auroras our way this past week.

Oh, that I had been in the North last week, where the sky erupted with jaw-dropping displays. I could only watch those vicariously via webcams, such as the Explore.org Northern Lights Cam at the Churchill Northern Studies Centre.

But here in southern Alberta we were still treated to some fine displays across our northern sky. The image below is from March 1, from my rural backyard.

Fish-Eye Aurora (March 1, 2017) — A full-frame fish-eye lens image of the aurora on March 1 with curtains reaching up into the Big Dipper.

The Sun wasn’t particularly active and there were no coronal mass ejections per se. But a hole in the corona let a wind of solar particles through to buffet our magnetosphere, stirring up geomagnetic storms of Level 4 to 5 scale. That’s good enough to light our skies in western Canada.

Aurora over Frozen Pond — A 160° panorama of the main auroral oval to the north on March 2 about 11:40 pm MST.

Above is the display from March 2, taken over a frozen pond near home. I like how the Lights reflect in the ice.

This night, for about 30 minutes, an odd auroral form appeared that we see from time to time at our latitudes. A wider panorama shows this isolated arc well south of the main auroral oval and forming a thin arc stretching across the sky from west to east.

Aurora Panorama with Isolated Arc — A 220° panorama of the isolated arc to the west (left) and east (right) and the main auroral oval to the north.

The panorama above shows just the western and eastern portion of the arc. Overhead (image below) it looked like this briefly.

Isolated Auroral Arc Overhead — The overhead portion of the isolated arc at its peak.

Visually, it appeared colourless. But the camera picks up this isolated arc’s usual pink color, with a fringe of white and sometimes (here very briefly) a “picket-fence” effect of green rays.

Isolated Auroral Arc West — The western portion of the isolated auroral arc at its peak.

This is the view of the isolated arc to the west. Erroneously called “proton arcs,” these are not caused by incoming protons. Those produce a very diffuse, usually sub-visual glow. But the exact nature of these isolated arcs remains a mystery.

As we head into solar minimum in the nest few years, displays of Northern Lights at lower latitudes will become less frequent. But even without major solar activity, last week’s displays demonstrated we can still get good shows.

September 7, 2016September 7, 2016

Sweep of the Auroral Oval

Arc of the Northern Lights

The aurora has been lighting up our skies a lot in recent nights, in a great sweeping arc across the northern sky.

It’s been a good week or so for Northern Lights, with several nights in a row of fine displays. These images are from one night, taken near home in southern Alberta, on September 2.

The lead image at top shows the display at its best, with the arc of curtains reflected in a nearby pond. The green curtains fade to shades of magenta as they tower into the high atmosphere, as one process of glowing oxygen giving off green light transitions to another emitting red light.

Concentric Arcs of the Auroral Oval — A 180° panorama of the Northern Lights exhibiting classic concentric ars across the north, with an isolated arc to the east at far right. This is a stitch of 10 segments, each 2-second exposures with the 20mm Sigma Art lens at f/1.6 and Nikon D750 at ISO 3200. Stitched with PTGui.

A little later the curtains had changed form, into a more homogenous arc above a set of sharper curtains below that are farthest north. People in northern Alberta or the Northwest Territories would have been seeing these curtains dancing above them.

What we are seeing is the classic curving arc of the auroral oval, the ring of light created by electrons raining down into our atmosphere in roughly an oval sweeping across the continent and centred on the magnetic pole in the Canadian Arctic.

However, at right, you can see a odd detached bit of more southerly aurora, with a dominant red colour.

Isolated Auroral Arc #2 (Sept 2, 2016) — An isolated auroral arc to the east on September 2, 2016, shot from near home during a fine display with active curtains to the north at left. A single 8-second exposure with the 20mm lens at f/1.4 and Nikon D750 at ISO 3200.

This is a closeup, showing the characteristic form of these odd “isolated arcs” — usually featureless, often thin, without much motion, and often red.

Isolated Auroral Arc #4 (Sept 2, 2016) — An isolated auroral arc to the west on September 2, 2016, shot from home during a fine display with active curtains to the north. A single 13-second exposure with the 20mm lens at f/1.4 and Nikon D750 at ISO 3200.

Later, the arc had brightened and expanded to cross the sky. The above view is looking west from home, with the arc now displaying a mix of pink, white and green.

Isolated Auroral Arc #3 (Sept 2, 2016) — An isolated overhead auroral arc on September 2, 2016, shot from home during a fine display with active curtains to the north. The Summer Triangle stars stand out here due to high cloud fuzzing their images. A single 13-second exposure with the 20mm lens at f/1.4 and Nikon D750 at ISO 3200.

Here, we are looking up the isolated arc, with the impression of it being a thin sheet seen at an angle, with the bottom green component being closest and the red top being highest and farthest away.

Isolated Auroral Arc #5 (Sept 2, 2016) — An isolated auroral arc to the southeast on September 2, 2016, shot from home during a fine display with active curtains to the north. This one displays the classic picket fence apperarance, with fingers of green aurora that moved along the band during a time-lapse of the scene. A single 13-second exposure with the 20mm lens at f/1.4 and Nikon D750 at ISO 3200.

This is the view looking southeast to the strange aurora. For a time it broke up and displayed a “picket fence” formation. And it moved!

Just what these isolated arcs are is a mystery. They have been called “proton arcs,” under the assumption they are caused by incoming protons, not electrons. But while there are such things as proton arcs and auroras, they are diffuse and invisible to the eye and camera in normal visible light. So these features are not proton arcs.

Nevertheless, these odd arcs are not like the usual auroral curtains, and likely have a different origin. But just what is still the object of research. Images by amateur astronomers such as these can help in the study.

May 11, 2015May 11, 2015

The Red Aurora of May 10

A strange red arc of aurora moved slowly across the sky on May 10.

All indicators looked favourable early in the evening on May 10 for a good auroral display later that night, and sure enough we got one. But it was an unusual display.

From my site in southern Alberta, the northern sky did have a diffuse glow of “normal” green aurora that never did take much form or structure.

But overhead the aurora took the form of an arc across the sky, starting as an isolated ray in the southeast initially, then reaching up to arch across the sky with what looked to the eye like a colourless band.

But the camera showed it as a red arc, with just a fringe of green curtains appearing for a few minutes.

Be sure to click HD and enlarge the video to fill your screen.

The time-lapse movie shows the sequence, over about 90 minutes, with 170 frames playing back at 12 frames per second. You can see the red arc develop, then become more narrow, then exhibit a few green curtains. Then it fades away.

Large-scale pulses also brighten the whole sky momentarily.

The other images are individual frames taken during the evening, showing snapshots of the red arc development, as it became more narrow in structure and gained green curtain-like fringes.

Presumably the red structure was very high in the atmosphere while the green curtains attached to it that did appear hung down from the high-altitude red arc.

I shot all images with an 8mm fish-eye lens to capture most of the sky. The camera is looking north toward Polaris, with the Big Dipper almost directly overhead near the centre of the frames.

The main image at top is a star-trail stack of 80 frames showing the sky’s circumpolar motion around Polaris and the aurora blurred and blended over 45 minutes of motion. I stacked the frames with the Advanced Stacker Actions from StarCircleAcademy.com