Spring Time Aurora in Calgary
By Dr. Robert Berdan
April 26, 2012
The Aurora from directly below called a corona, photographed north of Calgary on April 24 around 12:30 am.
The sun undergoes a 22 year cycle where the magnetic poles switch from north to south. Following this cycle the number of sunspots varies from a maximum number of several hundred to no spots in an 11 year cycle. As the number of sunspots increases so does the frequency of the Aurora. The earliest records of sunspots seen with the naked eye dates back 3,000 years ago. These spots were usually seen around sunrise and sunset. Around 1610 Galileo (and other astronomers) reported seeing sunspots through the newly developed telescopes. We have been observing and counting sunspots ever since. The sunspots are cooler regions on the surface of the sun that represent regions of intense magnetic fields. These fields twist and turn and can lead to an ejection of electrons and protons that form the Solar Wind. As the solar wind interacts with the earths magnetic field these particles interact high in our atmosphere with atomic oxygen and nitrogen in the Ionosphere. The interaction of these particles with Oxygen and nitrogen result in the emission of light which is most often green, but can include violet and reds that can be seen on clear nights.
Aurora north of Calgary in the Bearspaw region taken from highway 1A on April 24th. The aurora is forming a band in the north and also moved up high overhead. The main colors are green with a tinge of violet near the top. The orange-red clouds are caused by light from the city of Calgary reflecting off of them.
The Aurora is seen almost nightly on clear skies in the north in a region called the auroral oval. Yellowknife, my favorite place to photograph the aurora, sits directly beneath the auroral oval. Locations further south can also view the Aurora when the sun produces a solar storm that ejects more protons and electrons than normal. Solar storms are constantly monitored because they can potential destroy satellites and electrical transformers. When there is a solar storm or solar flare we have between 8 minutes to two days notice depending on how fast these highly charged particles are travelling. The earth is protected in large part from the solar wind by a magnetic barrier, however the barrier channels the charged particles towards the poles. When the solar wind is particularly strong and the earths and suns magnetic fields intertwine this can result in an Auroral display that can be seen as far south as the equator.
Chart showing the disturbance of the Earth's magnetic field by the solar wind. When the disturbance reaches orange and red there is strong probability of an Aurora around Edmonton and Calgary - this is the chart for April 23, 2012.
On April 23, I received an Aurora alert by email from aurorawatch at the University of Edmonton. Anyone can subscribe to this free service and receive an alert when there might be a chance to observee the Aurora. There are also several other sites including spaceweather.com and the Canadian Space weather forecast that you can check for the probability of an aurora. The best time to view the Aurora is usually around midnight on a clear dark night. This means when the moon isn't full and there are few clouds in the sky. For the conditions to be just right also takes some luck, but when the display is spectacular there are few natural phenomena that can match it.
11:30 pm a friend (Kamal Varma) stands in front of a vacant field north of Calgary while photographing the Aurora.
Most of the lights on the ground are due to oil rigs. The aurora formed a green and purple band in the north.
Around 11 pm looking West on Glendale Road. The bright star is Venus and the glow around it is from clouds
and moisture in the air. The aurora is just starting and is pale green. To the human eye the bands are sometimes barely discernible, but to the digital camera a 10-30 second exposure (ISO 1600, F1.4 to F4 lens) makes the color and bands more easily visible due to the longer exposure. The human eye has an equivalent shutter speed of 1\30 of a second so the camera is much better at seeing dim colors.
A car streaks by on highway 1 A with the Aurora and Bearspaw in the background.
The best time to see the Aurora is in the Spring and Fall because at these times the earths magnetic field and that of the sun are connected through magnetic ropes that channel the solar wind toward the earth. Also this year and next will be particularly good because we are heading into Solar Max a time when the greatest number of sun spots appears. Solar max is predicted to be around June, 2013. So far the next 2-3 years the aurora will be more common especially in regions south of the Aurora oval. However keep in mind the further south you live, the fewer chances you are likely to have and even if you do live further north most of the time you need to get away from city lights to observe them. To photograph the Aurora you need a single lens reflex camera, a tripod and wide angle lens with F4 or faster lens at ISO setting of 800-1600. Exposure times can vary depending on your equipment and how bright the Aurora is. I often use from 1 sec to 60 seconds and it is easy to take a few pictures with your camera and view the optimum exposures on your LCD screen. Remember to focus your lens on infinity, if possible use manual focusing, and no filters. If your camera offers Live View you can point your camera at a bright star, zoom in on it and then adjust the lens so the star is as small as possible this will provide perfect infinity focus so the stars are sharp. See my other articles on Aurora photography, time-lapse photography and photographing star trails for more details on photographing the Aurora Borealis. RB
Online version of the Calgary Herald featured some of these photos on April 24th.