By Eamonn Keyes

September 6th. The Orkney Distillery, Kirkwall.

Physics Distilled was once more a combination of two very different lectures- no bad thing- and the second of these, Forensics by Dr. Kat Tennick, I have previously covered as it was essentially the same lecture given by her partner Adam Wilcox on the opening night of the Festival. 

The talks took place upstairs in the Orkney Distillery, the home of my favourite gin Kirkjuvagr Orkney Gin.

The opening talk was given by Charlotte Proverbs, current completing a PhD at the University of Central Lancashire in Astrophysics on Sunspot Analysis. The topic of her talk was The Aurora, a subject many Orcadians will be very familiar with given the frequency of this phenomenon in our skies, particularly recently.

The aurora is conspicuous in Norse mythology, giving rise to several interpretations, from the Bifrost Bridge and the reflection of the armour of the Valkyries to the last breaths of dying warriors. Scientifically, it is the interaction of charged particles from the Sun with the magnetosphere surrounding Earth. These charged particles are ejected from the Sun by events such as a Coronal Mass Ejection (CME)   or the Solar Wind causing geomagnetic storms as it slams into Earth’s ionosphere. The particles are deflected towards the poles of Earth by our planet’s magnetic field and interact with our atmosphere, depositing energy and causing the atmosphere to fluoresce. 

In the northern hemisphere it is called the Aurora Borealis, and in the southern hemisphere it is the Aurora Australis. The aurora has now been seen to take place on other planets such as Jupiter, Saturn and Uranus.

The bright colours of the aurora are dictated by the chemical composition of Earth’s atmosphere. 

Green aurorae are typically produced when charged particles collide with high concentrations of oxygen molecules in Earth’s atmosphere at altitudes of around 60 to 190 miles (100 to 300 km).

Red aurorae are comparatively less frequent and are usually associated with intense solar activity, occurring when solar particles react with oxygen at higher altitudes, generally around 180 to 250 miles (300 to 400 km). At this height, oxygen is less concentrated and is excited at a higher frequency or wavelength, making reds visible. Red auroras are often seen at the higher edges of the display.

Blue and purple aurorae are even less common and also tend to appear during periods of high solar activity. They are produced when solar particles collide with nitrogen in Earth’s atmosphere at an altitude of 60 miles (100 km) or less and tend to be visible toward the lower parts of the display. 

Yellow and pink aurorae are rare and are typically associated with high solar activity, with their colours resulting from a mixture of red aurorae with green or blue aurorae. 

Some may remember the geomagnetic storm of 10-13 May 2024 that resulted in an exceptional auroral display. Three CMEs originating from solar active region 13664 erupted, reaching Earth on May 10^th,  causing severe to extreme geomagnetic storms with bright and very long-lasting aurorae.

The geomagnetic storm was so intense that the Aurora Borealis was seen as far south as Hawaii, China and Africa, and the Aurora Australis was seen as far north as Australia, Chile and South Africa. GPS signals were disrupted and some satellites temporarily stopped functioning.

This still falls short of the most intense geomagnetic storm recorded, known as the Carrington Event, which took place in September 1859. In August 1859, astronomers around the world watched with fascination as the number of sunspots on the solar disk grew. Among them was Richard Carrington, an amateur astronomer in a small town called Redhill near London in England.

On Sep. 1, as Carrington was sketching the sunspots, he was blinded by a sudden flash of light. Carrington described it as a “white light flare”. The whole event lasted about five minutes.  Usually it takes 2-3 days for a CME to reach the Earth, but this was so energetic hit our planet in 17.5 hours.

The day after Carrington observed the impressive flare, Earth experienced an unprecedented geomagnetic storm, with telegraph systems going haywire and auroral displays — normally confined to polar latitudes — visible in the tropics. Magnetometers frequently went off their scales and telegraph systems became inoperable. Despite being disconnected, the current induced by the storm enabled a conversation to take place via telegraph for two hours between Boston and Portland Maine. The damage a Carrington Event type storm would cause today would be massive given the ubiquity of electrically powered and otherwise sensitive equipment that now exists in our society. Currently during major storms astronauts in space have to hide in radiation proof shelters, pilots in aircraft are advised to fly lower and there is the possibility that satellites in low earth orbit might begin the re-entry process.A daily brief on the state of solar activity is available on www.spaceweather.com.

Sunspot activity rises and falls on an 11-year cycle, and we are currently approaching the next solar maximum in 2025. So now is a very good time to look at the worst solar storms and the marvellous aurorae they can generate. Photos taken even on camera-phones will show the colours of the phenomenon, as the photos below, taken by me in Kirkwall during the geomagnetic storm of May 10^th 2024 show.