Beautiful Rays Of Aurora Dapple The Dawn Sky

At 4:45 a.m. CDT this morning (Aug. 27) spectacular rays erupted from a low, bright green arc and paraded across the northern sky. Credit: Bob King

Maybe it’s because of the name aurora, which means ‘dawn’, but that’s exactly when the northern lights put on one great show this morning. With clouds constantly a bother this late summer, many of us have been thwarted in viewing all manner of conjunctions, comets and moonrises. Not this morning. I was determined to see Comet Oukaimeden near Orion just before dawn. And that’s exactly how I happened to be up to catch a surprisingly fine aurora.

A striking green arc perforated by many needle-like rays. Credit: Bob King

One of the keys to maximizing enjoyment of the aurora is to have a place you can get to with a low northern horizon. At least from mid-northern latitudes, lots of activity often occurs very low in the northern sky.

High speed electrons from the sun spiral down individual magnetic field lines in Earth’s magnetic bubble called the magnetosphere to create multiple parallel rays when they strike oxygen and nitrogen atoms in the upper atmosphere. Credit: Bob King

We were already primed for northern lights because of the NOAA space weather forecast, so when I looked out the window at 4 a.m., there they were.

I jumped in the car and sped to a country road not far from home. Arriving around 4:30 a.m. several pale green arcs snaked across the north, and within minutes they erupted with massive parallel rays. To the eye, the tall rays were colorless, but they loved the time exposure afforded them by the camera.

The pictures were taken using a 17mm lens at f/2.8, ISO 800 and exposure times around 15 seconds.

While I did get to see my comet in the nick of time, the northern lights made it more than worth my while. I hope you got to see them, too.

Jupiter (lower left next to the star Delta in Cancer) and Orion (upper right) sparkle in the dawn sky over Duluth, Minn. Wednesday morning. Credit: Bob King

The display continued deep into twilight and no doubt carried into darker skies farther west of my location. There’s still a possibility for minor auroras early tonight. I hope so. Two 4 a.m. stints in a row would kill me.

11 Responses

  1. Mistahbue

    These are breathtaking!!! How far north of the cities were you? I’m down just a smidge past Hinckley – hope they are visible this far south tonight!!!

    1. astrobob

      Hi Mistahbue,
      I was about 10 miles north of Duluth. These would have been visible from Hinckley no problem.

  2. Dominik

    Hello Bob,

    just a short question, do you know why blue/violet auroras are so relatively rare even though the atmosphere is made up off 78% nitrogen which basically emits blue/violet light when excited?

    1. astrobob

      Good question. It’s a combination of factors. Oxygen atoms, which emit red light in the high atmosphere, dominate over nitrogen in the upper atmosphere. Most of the atmospheric nitrogen is in molecular form (N2) and very stable, so it doesn’t get excited like oxygen atoms. Also, in general, the nitrogen that does get excited by incoming solar electrons (nitrogen molecular ions in the high upper atmosphere and molecular nitrogen in the lower atmosphere during exceptionally intense auroras), emits in the blue and red end of the spectrum, where our eyes are less sensitive. Oxygen emits a lot of green light in exactly the part of the spectrum our eyes are most sensitive to, so that emission dominates.

      1. Dominik


        thanks a lot for the answer. That was a very good explanation. The more I think about this topic the more complicated it seems.
        Like that oxygen which exists in the upper atmosphere emits low energy red photons compared to low level oxygen which emits higher energy green photons. Even though the radiation at higher altitudes is greater and so the electromagnetic energy.
        Anyway blue is my favorite color and so seeing a beautiful blue aurora is one of my dreams

        1. astrobob

          You’re welcome. Much has to do with the quantum levels in the oxygen atoms. To emit red light, oxygen has to be ‘left alone’ from collisions of other molecules and atoms, so it can take the 110 seconds for its electrons to drop to the lowest level and emit a red photon. In the lower atmosphere, there’s too much jostling from other molecules and consequent energy absorption for oxygen to emit red. It needs the rarified environment of the high atmosphere.

          1. Dominik

            Can’t reply to your last comment so I’ll have to reply to this one.
            Anyway, yes it’s indeed quite complicated.
            But that’s the fun about physics. There’s always more to learn, deeper knowledge of the universe to uncover.
            That’s why I love physics.
            I’m just not too friendly with the mathematical aspect of it all, I still have to get used to that haha.

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