Labor Day Weekend Auroras / Volcanoes Turn Sunsets Purple

An aurora during a previous G2 storm that made for a nice show in northern Minnesota. Bob King

With the moon only the thinnest of crescents at dusk this weekend, the stage is set for a possible auroral display. Space weather forecasters predict a moderate or what’s called a G2 storm for Saturday night, Aug. 31. The storm will be strongest — at least according to the forecast — before midnight Central Time. It will continue into the wee hours of Sunday morning (Sept. 1) and possibly spill over into Sunday night. Canada, northern Europe and the northern half of the U.S. are favored.

The keyhole-shaped coronal hole partially responsible for this week’s happy forecast. Photo taken by NASA’s orbiting Solar Dynamics Observatory late on Aug. 28. NASA

G2 storms usually feature both arcs and active rays that expand and swirl in the lower half of the northern sky. Watch the forecast and if it’s clear, keep an eye out both nights for activity. The sun hasn’t sported a sunspot for 21 days and although we’re approaching the minimum of its 11-year cycle, the time when it’s least active, our star never stops blowing a steady stream of subatomic particles into space called the solar wind.

It’s these particles that are headed toward Earth right now. They flow from an opening in the sun’s otherwise buckled-down magnetic canopy called a coronal hole. A big one has been facing us this week. It and a CIR (Co-rotating Interactive Region) — a fancy name for a compressed region that forms when a faster wind slams into an earlier slower wind — are behind the exciting forecast. Material can pile up in a CIR and produce intense magnetic fields that excite auroras when it breezes by the Earth.

People often ask me where the best place to go is to see the aurora. Mostly, it anywhere out of town. But your best best is travel north of the most intense city light pollution to a darker, more rural location. Find a spot with a good view of the northern horizon. Some auroras are extremely active but only in the bottom 20° of the sky. 20° is equal to two fists held one atop the other at arm’s length.

I highly recommend using this Light Pollution Map to help your identify an “aurora refuge.” Red, orange and yellow indicate areas of intense to moderate light pollution. Green and gray areas are much darker. I try to find a quiet country road, pullout, field or parking lot. Bring a friend for a sense of security if you’re not familiar with the area.

Astronauts on the International Space Station took this photo on June 22, 2019 when the Raikoke volcano erupted on the Kuril Islands, sending a plume of volcanic ash and sulfurous aerosols into the stratosphere that are behind recent colorful sunsets. NASA

There’s more than just the aurora lighting up the atmosphere these days. Several evenings ago I noticed a richly-colored purple-pink glow in the western sky about 15 minutes past sunset. I hadn’t seen that color for a long, long time and immediately thought volcanoes. Big ones can shoot ash-laden plumes of sulfurous gas high into the stratosphere. The material scatters blue light which mixes with the red of sunset to produce a purple pall in the west.

I hope this translates on your screen. On mine it’s a close match to the color I saw with my eyes. I took the photo during the peak of the “purple light” in the western sky about 15 minutes after sunset Aug. 28, 2019. Bob King

Checking, I discovered that the Raikoke volcano in the Kirul Islands and the Ulawun volcano in New Guinea blasted gases and dust more than 11 miles (18 km) high on June 22 and Aug. 3rd, respectively. So it was volcanoes!

On Wednesday night (Aug. 28) I drove to an open field and watched the western sky starting at sunset. I first noticed a pale, pinkish-orange blush about 30° high (three fists) over the sunset point 10 minutes after sundown. It deepened into a vivid, rosy-purple glow about 30° across that reached greatest intensity about 15 minutes after sunset. Closer to the horizon the sky glowed the color of cantaloupe. Straining my eyes, I could see faint striations or bands nearer the horizon which may have been volcanic dust. Next time I’ll bring binoculars!

Later, about 25 minutes past sunset, the purple light had disappeared, but the area above the horizon glow an intense cantaloupe. Bob King

20-25 minutes after sunset, the purple glow had disappeared, but the orange-pink twilight light lingered within 15° of the horizon. Totally gorgeous! I encourage you to have a look — the sight is also easy to capture on a mobile phone.

3 Responses

  1. Edward M Boll

    What a way to start September. There are also a number of comets getting well placed in our Hemisphere. And although 168 has not been seen yet, T2 Panstasrs may be a binocular comet next Spring.

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