Why Was The Aurora Out Last Night?

The sun is nearly blank around 8:30 a.m. (CDT) today with only one obvious sunspot group to the lower left. With few spots, don’t expect much much auroral activity … then again, you never know. Credit: SDO/NASA

I will never figure out the aurora. Most of the time there’s a clear connection and forecast indicating that a flare or coronal hole on the sun will have a certain probability of zinging the Earth’s magnetic field. That might precipitate a display of the northern lights anywhere from the high Arctic to as far south as Arizona.

Like the weather forecast, sometimes space meteorologists get it wrong though not for lack of trying. Nature does not always follow expected pathways despite the best available data and computer modeling.

Around 12:30 this morning (June 25) the northern sky was  aglow with a very low green arc and faint, streaky rays. Details: 35mm lens, f/2.8, ISO 2000 and 30-second exposure. Photo: Bob King

Last night northern lights were not in the forecast. The Kp index slumbered around 2 and space weather experts predicted quiet conditions. I even checked the POES satellite map to gauge the extent of the auroral oval and found it nestled far to the north above Hudson Bay. So why did the aurora make an appearance?

The low green arc shows up well in this 30-second exposure with the camera pointed due north around 1:30 this morning. Photo: Bob King

The northern sky up to about 20 degrees (two fists) glowed with colorless, amorphous light punctuated by occasional faint rays that rose like wisps of smoke from a smouldering campfire. This went on until at least 2 0’clock.

The Earth “wears” a crown of aurora borealis centered on magnetic north and south called the auroral oval. This photograph from space shows the southern oval over Antarctica. Credit: NASA

After scratching my head about the matter this morning, I decided to call Joe Kunches, a space scientist at NOAA’s Space Weather Prediction Center. He boiled it down to this: even though aurora wasn’t in the forecast, the constant wind of electrons and protons streaming off the sun (solar wind) “always causes some level of activity in Earth’ s polar atmosphere.”

Electrons in the wind excite the atoms of the upper atmosphere to give off characteristic auroral greens, reds and purples.

This permanent aurora is called the auroral oval; it normally resides in the high Arctic (and Antarctic) but expands further south over the U.S. during periods of enhanced solar activity.

Given dark skies and no moon, conditions were ideal to see even a minor aurora last night. Still, we both remained puzzled as to why the aurora was visible as far south as Duluth when magnetic indicators and satellite maps showed it residing far to the north in the oval.

“You shouldn’t have seen it,” Kunches joked. With that, we both had a good laugh.

6 Responses

    1. astrobob

      Hi Mike,
      I was just out and saw a suspicious glow in the north. It was very late, and as displays go, this one was pretty minor.

  1. Kim Breimeier

    Well darn it! We thought we saw them last night but after looking at the forecast and the oval decided it was just fog or low clouds and went to bed!

  2. Andrew Kirk

    Living too far south for Aurora, I settle for brilliant Venus and bright Jupiter at dawn. Around 5AM they’re awesome. Venus has traveled a long way since its transit of Sol.

    1. astrobob

      Andrew,
      Glad to hear you’re keeping an eye on those two. I plan a morning jaunt soon for a look.

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