What is that we’re seeing up in the sky?

July 21, 2015

 

Jordan Smith
Zenith News

Towards the end of June, Northlanders were treated to a view of the Northern Lights. While this spectacular show is a simple pleasure, it is not a simple phenomenon.


The Northern Lights occur only in the Northern Hemisphere, where they are known as Aurora Borealis. Their counterpart in the Southern Hemisphere is the Aurora Australis. Both are most common near their respective poles, and their likelihood of occurrence steadily decreases as you move towards the equator.


Auroras look like a luminous curtain, stretching east and west. In middle latitudes, it appears as a dark red glow near the poleward horizon, but this is uncommon here since we are closer to the North Pole than the equator. Green is the dominant color of auroras in our neighborhood, and, although they most commonly occur in the northern sky, they are known to cross the zenith, extending into our southern sky as well.


Auroras are strongest during sunspot activity arising from magnetic storms. The bottom of the auroral curtain reaches as low as 62 miles above the earth’s surface, while the top stretches as high as 190+ miles above ground level. Satellite images depict them as oval belts surrounding the geomagnetic poles.


Auroras result from large-scale electrical discharge processes fueled by the electromotive force generated by the interaction between solar winds and Earth’s magnetic field. The luminosity comes from atoms and molecules that are excited, or ionized. Energetic electrons carrying the discharges are channeled towards the poles by the magnetic field, colliding with and exciting (ionizing) upper atmosphere atoms and molecules.


The green of energized oxygen atoms is the most common visible manifestation, but oxygen molecules account for reds and yellows. Nitrogen atoms give off a purple light, and nitrogen molecules are responsible for a pinkish hue.


When the electrical field on either side of an auroral curtain is induced by electrons, the result is the common appearance of a curtain like luminosity. North of the “curtain,” the field is directed southward and vice-versa, causing the ionized air on either side to flow rapidly in opposite directions, causing what appear to be folds in the “curtain.”


There are sometimes 27-day intervals between auroral displays because the sun makes a complete turn on its axis approximately every 27 days. A solar wind, generated by a solar flare, can enhance an auroral discharge, causing both Northern and Southern Lights to extend farther from the poles towards the equator.


As the sunspot period declines, a somewhat intense beam of solar wind can blow out from a quiet region on the sun, lasting a few months to two years. So every 27 days, this beam might be aimed at our planet, resulting in the 27-day intervals of auroral activity.


For reasons not fully understood, this activity also has pronounced seasonal variation, reaching a maximum during the equinox months of March and September. Auroral activity is not continuous, repeating a quasi-cyclic display lasting only a few hours.


The Nothern Lights can easily be observed with the naked eye, as can sundogs, or parhelia. When high cirrus clouds move in, the sun or moon may develop a halo—the result of light refracting through lens-like ice crystals in the clouds. If these clouds thicken, sundogs sometimes appear to be as bright as the sun itself. If you see what appears to be part of a rainbow in close proximity to the sun, that would likely be a sundog.


In the hour after dusk or before dawn, there is a higher likelihood of spotting artificial satellites, as this is the time when sunlight can reflect off them. These are not television satellites, which are in a geosynchronous orbit, meaning their orbital speed matches that of the earth, ensuring they remain fixed above the same point on Earth’s surface at all times. Beyond this, however, at 22,300 miles above us, you will not be able to see one with the naked eye anyway.


Finally, if you see a UFO, it’s best not to assume we are being invaded by extraterrestrials. Anything that appears to be flying and cannot be identified is an Unidentified Flying Object. Most UFO reports come from inexperienced sky watchers. The planet Venus, when viewed in the evening sky, has often been mistaken for a UFO. The more familiar you are with observing the sky, the less likely you are to spot a UFO.


And now for the outlook for the next two months, which may turn out a tad warmer than usual: Look for a slight cool-down as July draws to a close. Things should heat back up in August, with a decent amount of showers and thunderstorms, but enough fair weather to get out and enjoy the rest of the summer.

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