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First, let's look at that alert. A high-speed stream of solar material from a large coronal hole will arrive overnight July 5-6. When it slams into Earth's magnetic field, space weather experts expect a G1 (minor) geomagnetic storm that could produce auroras visible across the northern U.S. and southern Canada.
The most recent G1 storm, on Friday, July 1, was a doozy, with tall rays that reached halfway up the northern sky and a vibrant, green arc at the horizon. That aurora persisted from dusk till dawn. Let's hope we get lucky again. The current forecast predicts elevated activity between 10 p.m. and 1 a.m. CDT, Tuesday night (July 5), with the G1 storm starting around 1 a.m. and lasting into dawn. No worries from the moon — it's only a half and sets around 12:30 a.m.
This aurora or any aurora for that matter presents an opportunity to do science. Dr. Ryuho Kataoka of the National Institute of Polar Research (Japan) and colleagues described their project to take stereo image pairs of the northern lights from Alaska several years back. They set up Nikon D4 cameras equipped with 8-mm f/2.8 fisheye lenses at two locations 5 miles (8 km) apart and aligned north-south at Poker Flats Research Range and the Aurora Borealis Lodge near Fairbanks, Alaska.
The two cameras operated as an artificial pair of eyes set wide enough apart to see the aurora in three dimensions. Each captured the sight from a slightly different angle. When combined into a stereo pair they show the aurora in true 3D. People used to use stereoscope viewers to merge photographs of natural vistas and portraits taken from slightly different points of view into remarkably realistic 3D scenes. Our generation has taken the next leap with virtual reality.
You probably don't have a stereoscope sitting around the house, but you don't necessarily need one either. With a little practice you can see the 3D effect with just your eyes.
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Sit back in a chair one to two feet (30-60 cm) from your monitor with the aurora-pair photo in front of you. Then relax and stare into the distance. Gradually cross your eyes, and you'll see the two separate images float off the screen and blend into a single image in three dimensions. I perceive the brighter parts as closer, with the stretchy ray tops higher up and farther away. If you're having difficulty, here's a great primer on learning how to "free-view."
Of course, the Japanese team wasn't only interested in creating stereoscopic images to share with the public. They also wanted to use the subtle differences in perspective to measure the height of different types of auroras.
From their study they determined that the typical altitude of the rayed structure common to auroral displays was 62-81 miles (100-130 km) high. The pulsating, patchy aurora, which tends to occur in the early morning hours after the main storm, forms lower at just 50-55 miles (80-90 km) altitude. Why? Electrons that produce the pulsating aurora strike our atmosphere at higher speeds with greater energy and burrow deeper into the atmosphere.
I was intrigued by the study because it wouldn't be difficult for two (or more) amateur photographers with digital SLR cameras to do exactly the same thing: take pictures of the aurora in the same region of the sky with the same lens and settings at the same time. Using an imaging program like Paint or Photoshop they could be placed side-by-side to make stereo pairs. As per the Japanese researchers, the two photographers would be positioned some 5 miles north-south of one another.
Sounds like a great project for the next northern lights show! Find more information on how to make your own stereo pairs at waynesthisandthat.com .
"Astro" Bob King is a freelance writer for the Duluth News Tribune.
