A prominence on the edge of the Sun on the morning of 13 May 2011 (Australian time) photographed in the red light of hydrogen atoms. Image and copyright Monty Leventhal OAM ©, all rights reserved
Monty Leventhal OAM has been observing and imaging the Sun for well over a decade. Here are a few more of his images taken in the first half of 2011 recording the awakening of the Sun from its recent deep minimum of activity.
Two of the images record prominences on the edge of the Sun. These show hot gases flowing along magnetic field lines. As most of the Sun’s gas is hydrogen these atoms radiate in the red light of hydrogen and can only be seen through special filters, known as hydrogen alpha filters, that block all other light except that from hydrogen atoms. Prominences can only be seen like this when they are at the edge of the Sun so that there is no light behind them. If they are not at the edge and they are projected against the bright solar disc than we see them as dark lines called filaments.
A prominence on the edge of the Sun on the morning of 17 March 2011 (Australian time) photographed in the red light of hydrogen atoms. Image and copyright Monty Leventhal OAM ©, all rights reserved
Prominences extend up into the Sun’s outer atmosphere or corona where the temperature is around a million degrees Celsius. In contrast the gas in the prominence is only about 10 thousand degrees Celsius. Why doesn’t the hot corona heat up the gas in prominences? Former CSIRO solar physicist Ronald Giovanelli explains in his 1984 book, Secrets of the Sun, that ‘the flow of heat across a magnetic field is very slow’ so that ‘prominences are then insulated on their extensive sides’.
A flare on the Sun on the morning of 22 April 2011 (Australian time) photographed in the red light of hydrogen atoms. Image and copyright Monty Leventhal OAM ©, all rights reserved
Flares are explosions on the Sun that can be seen as brightenings of the solar surface, especially when viewed through a hydrogen alpha filter. During an explosion high-energy radiation such as X-rays can also be released. Scientists consider that flares are related to magnetic fields: when complex magnetic fields in a region of the Sun reorganise themselves into a simpler, lower energy state then energy is left over that is released in the flare.
Over the next few years the activity on the Sun can be expected to keep increasing until it reaches a maximum. We can look forward to many more images recording solar activity from Monty.