Aurora Watch: A Mighty Wind Comes Our Way

This large coronal hole in the sun's atmosphere and its extension to the south are responsible for the forecasted uptick in auroral activity in the next few nights. We can't see coronal holes in visible light, but they show up clearly in far ultaviolet as in this photo taken by NASA's orbiting Solar Dynamics Observatory. Credit: NASA/SDO
This large coronal hole in the sun’s atmosphere and its extension to the south are responsible for an expected uptick in auroral activity the next few nights. We can’t see coronal holes in visible light, but they show up clearly in far ultaviolet as in this photo taken by NASA’s orbiting Solar Dynamics Observatory. Credit: NASA/SDO

Call it a gale of subatomic proportions. Once again, a gaping hole in the sun’s corona has unleashed a wind of electrons and protons bundled with magnetic energy toward the Earth. The blast touched off a minor geomagnetic storm earlier this morning with spillover expected tonight. After a lull, storming is expected to resume tomorrow morning (Sept. 28) and continue straight into the night. We can expect the best of it — a moderate or G2 storm — Wednesday evening, Sept. 28 from nightfall through 1 a.m. Thursday morning (Central Daylight time). Here’s the official forecast.

This is a view of the back a digital SLR camera that shows the location of the live view button that you can use to see bright stars on your back viewing screen and focus on them for sharp nighttime photos. The magnifying glass enlarges the live view, making focusing even easier and more precise. Credit: Bob King
This is a view of the back a digital SLR camera that shows the location of the live view button that you can use to see bright stars on your back viewing screen and focus on them for sharp nighttime photos. The magnifying glass enlarges the live view, making focusing even easier and more precise. Credit: Bob King

Basically, the next three nights look ripe for displays of northern lights. As long as the weather’s clear, conditions are ideal for viewing with no moon to brighten the sky. Get your cameras ready! You’ll need a tripod to use as a steady mount and a camera that can take time exposure photos up to 30 seconds long. Since autofocus cameras struggle to focus on stars, set both the lens and camera in manual mode. Then, either pre-focus on a distant cloud earlier in the day and leave the lens set at that position or use the live view option button on the camera back to directly focus on a bright star using the back viewing screen.

Many DSLRs have a B (bulb) setting for exposures longer than 30 seconds. When using the B setting, consider buying a cable release device that locks the camera shutter open without needing to use your fingers. Credit: Bob King
Many DSLRs have a B (bulb) setting for exposures longer than 30 seconds. When using the B setting, consider buying a cable release device (right) that locks the camera shutter open without needing to use your fingers. Credit: Bob King

Set the camera’s light sensitivity to ISO 800 or 1600, the lens to its widest setting (something like f/2.8, 3.5 or 4) and compose the scene. Wide angle lenses are best for covering the the large auroral forms. You can either select the length of the exposure on your camera’s display or using a dial. If you have a “B” setting, that stands for “bulb”. In “B”, you can hold the shutter button down for as long or as little as you like. As soon as you let up, the exposure is over. Better, purchase a cable release-type device on Amazon or eBay or your local camera store that will do the pressing for you without having to worry about shaking the camera.

Auroras are caused when particles in a strong solar wind, like the one blowing from this week's coronal hole, link up with Earth's magnetic field
Auroras are caused when the solar wind (yellow and green lines), like the one blowing from this week’s coronal hole, connect with Earth’s magnetic field (blue loops). The green spot represents the connection.  The bond snaps the field line and allows solar particles (green sparkles) to stream down to the polar regions to create the daytime aurora. The nighttime aurora occurs when the gusty solar wind pushes the snapped field line(s) to the shadowed side of our planet, where they fold back and reconnect (see below). The energy of the reconnection propels particles into the nightside atmosphere to spark the familiar aurora. Credit: NASA

I like to start exposing at f/2.8 with an ISO of 1600 and exposure around 15 seconds then decrease or increase the length depending on what I see on the replay. At that ISO I rarely go longer than 25 seconds.  If the image looks too dim, increase the exposure. If too bright, cut it back. Since electrons are cheap, shoot lots of photos to get something you like!

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The green arcs represent the Earth’s snapped magnetic field lines that carry along particles from the solar wind. When they pinch back together on the nightside of the planet, the reconnection (green blob) generates the energy that shoots solar wind particles both toward the Earth, to create the northern and southern lights, and outward to the right into space. Credit: NASA