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Best auroras in years spotted over parts of Canada



The aurora over Alberta on May 28, 2016. Credit: Theresa and Darlene Tanner

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Scott Sutherland

Meteorologist/Science Writer

Monday, May 29, 2017, 4:57 PM - The brightest and most intense auroras since 2015 were spotted over parts of Canada this past weekend, much to the delight of photographers seeking to capture these amazing displays. See them here!

Aurora photographers Theresa and Darlene Tanner captured some amazing images on Saturday, from Alberta, that they say are the best they've seen since September of 2015!

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So, what happened?

Nearly a week ago, on May 23, the Sun unleashed a relatively small and slow-moving cloud of plasma from its surface, known as a coronal mass ejection, and space weather forecasters were anticipating at least part of this cloud affecting Earth.



The view of the Sun's corona and the May 23 Coronal Mass Ejection, from SOHO's LASCO 3 coronograph. The empty disk is the coronograph shield, to block direct sunlight from entering the detector, and the dark band to the upper right is the arm holding the shield in place. Credit: NASA SOHO/Scott Sutherland

Although this CME was a fairly minor one, compared to some that the Sun blasted out a few years ago, during its more active period, when it finally reached Earth over the weekend, it appeared as through the densest part of it scored a glancing blow on the planet's geomagnetic field.



NOAA's WSA-Enlil Solar Wind Prediction model run, showing the arrival of the CME on May 26. The yellow dot is the Sun, the green dot is Earth, and the red and blue dots are the STEREO A and STEREO B satellites. In the upper panel, which shows the density of the solar wind, the ribbon of the CME is visible intersecting Earth's location in space. Credit: NOAA

When a large amount of solar material sweeps past Earth's geomagnetic field, charged particles from the cloud (electrons and protons) get caught up in the magnetic field lines, and these particles get funneled down towards the ground at the poles. There, they stream into the atmosphere, knocking into atoms and molecules of oxygen and nitrogen, and kicking them into highly energetic excited states. When the atoms and molecules dump that excess energy to return to a normal state, they emit the coloured light that we see (although light emitted due to proton collisions tends to be invisible ultraviolet light).

Atomic oxygen emits red light, nitrogen atoms emit blue light, and the combo of red and blue often shows up as purple. The nitrogen atoms can also kick out an electron, which can then impart energy to a nearby oxygen atom and the oxygen emits green light to get rid of that excess energy. Lastly, high energy electrons can pierce much deeper into the atmosphere and strike nitrogen molecules, and the light these molecules emit shows up as pinkish-white.

This event was a little unusual, as the Sun is entering the quiet phase of its 11 year cycle, and thus solar flares and coronal mass ejections, while they do still happen, tend to be more uncommon.

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Sources: TeamTanner | NOAA Space Weather Prediction Center | NASA | SpaceWeatherLive

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