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Environment

Our recent aurora spectacle

Many of us were thrilled by the recent auroras visible around the world including here in Whitianga. This rare sight is something we might be lucky enough to see again in the coming months and maybe even into next year as the Sun is entering the most active phase in its 11-year cycle.
 |  Alastair Brickell  | 

A pano image taken Saturday night 11 May taken by Tina Macrae.

The auroras were caused by an ejection of the sun’s outer atmosphere called a CME (coronal mass ejection) which is highly charged gas called plasma actually breaking off and travelling through space to interact with the earth’s magnetic field.

These CMEs originate in sunspots which are active areas on the sun, and they become more common during periods of heightened solar activity which occur over the 11-year cycle. The particular sunspot that was responsible for the recent spectacular auroras has now rotated around the sun and came back to face us this past week so there might have been further solar treats.

The heightened solar activity is expected to continue over the next few months as ‘solar max’ of the cycle is reached either this year or next.

This was a rare chance to actually see the earth’s magnetic field. This field is usually invisible to us, but very much in action, protecting us from potentially harmful, solar radiation by diverting the sun’s charged particles towards the poles, where they cause the upper atmosphere to glow. The colours are caused by gases in the atmosphere being turned into a plasma with blues and greens probably caused by oxygen and the reds and purple by nitrogen high in our outer atmosphere. The auroras are often best seen after midnight when we are looking towards the downstream tail of the Earth’s magnetic field where most of the action is occurring.

This magnetic field is very important to us as without a magnetic field of its own the Earth would have suffered the same fate as Mars which has virtually none. As a consequence of eons of geologic time, Mars has had its atmosphere steadily eroded away by solar storms and now has only a very tiny fraction left.

About the Colours: Some of us may have been disappointed that they did not see all these colours which are often very obvious in photos. The trouble is that our eyes are designed to work under daylight conditions and are very insensitive to colours when they are faint as is the case with auroras. Modern digital cameras or phone cameras are much more sensitive to colours at these low light levels and time exposures enhance this effect, producing the dramatic colours often seen in photos. The colours are real as they are caused by the fluorescing atmospheric gases but it’s just that our eyes cannot appreciate them unless the colours are exceptionally bright.

The sun’s varying activity is often considered to affect the earth’s atmosphere and weather and especially the ozone hole. However, it’s effects can even extend to the distant planet Neptune, where it has been linked to the11 year-long cyclic changes to cloudiness in its atmosphere and weather.

Another consequence of being near solar maximum is that the sun’s very active magnetic field deflects potentially harmful cosmic rays from us. These originate largely from exploding stars elsewhere in the Milky Way, our galaxy. This was very obvious to me as I was flying to and from the USA last month.

I often carry a Geiger counter with me on flights to record levels of these cosmic rays. On the most recent flights this level of radiation was about 20-30% less than normal, a very significant reduction.

Fun fact:

When you are flying, you can get 30-40 times the radiation you receive on the ground… but it’s virtually harmless for short periods.

So while the sun, our nearest star, may seem quite tiny in the sky, its changing state cannot only reach and affect us on a daily basis, but also distant planets like Mars and Neptune.

Alastair is the author of our weekly Star Gazers, page two of The Informer. He is a geologist and astronomer and recently went to the US to witness the total eclipse of the sun. Alastair and Harriett host and own Stargazers Astronomy Tours and B & B at Kuaotunu.