This page uses images from the LASCO coronagraph on board the ESA/NASA SOHO spacecraft.
A coronagraph is a specialised telescope that has a small opaque filter called an occulting disc, in the field of view. This filter is designed to block out the Sun so we can see the details of the solar atmosphere (Called the corona) which are normally washed out by the intense light of the Sun.
Vast explosions of solar plasma called Coronal Mass Ejections can be visible, and if fired towards Earth, can trigger the aurora!
At Dunedin Aurora we have created custom software to allow a computer to identify fast moving CMEs. We also process and save enhanced images for visual analysis. This is currently a "test" version of the software while we try to improve the quality of the detections.
We are awfully fond of our graphs at Dunedin Aurora! This particular chart shows detections of CMEs over the long term.
Figure 1 is a typical coronagraph image. The Sun is represented by the small white circle in the centre. The occulting disc is shown as blue disc. The shadow extending away at either the 2 o'clock or 8 o'clock position is the supporting vane for the occulting disc. The white radial features are streamers of solar plasma. CMEs appear as wave-fronts that billow out from the solar disc. CMEs that appear as a "smoke ring" are called Halo CMEs and indicate something travelling towards or away from Earth.
FIg 1 also is annotated to show the solar poles and the east and west limbs of the Sun. The two green circles mark a zone 2 - 3 solar diameters that is monitored for CMEs. I choose to monitor this area for two main reasons:
Future work will be about improving the balance between reducing noise and improving contrast.
Figure 2 shows the coronagraph image after it has been processed. Even after enhancement, a lot of detail is almost at the level of the noise floor in the image, so some visual "snow" still remains. The image's coordinate system is also changed, from a polar system, to a rectangular system. Radial zones and toroidal sectors in the original image become simple rectangles and make processing for features much simpler.
The last part of CME monitoring at Dunedin Aurora is determining coverage and any potential Earth impact. We monitor a zone between 2 and 3 solar diameters from the edge of the Sun. Sudden changes in the brightness over a set threshold indicate possible CME activity. The computer logs this and updates the website (and hopefully social media) as well as posting a dynamic link to the latest data from STEREO A - this can be used to confirm if a potential CME is heading towards or away from Earth. Eventually this process will be automated.