The Scientific Magic of Total Solar Eclipses

Atik cameras are proud to have a long-standing relationship with the Institute for Astronomy at the University of Hawaii. Shadia Habbal and her team have been using Atik cameras to photograph total solar eclipses since 2010 with absolutely stunning results. The upcoming eclipse on 20th March seemed like a good excuse to find out a bit more about their pioneering work – we wish them good luck and clear skies as they use the Atik 414EX to photograph it from Norway and look forward to seeing the results!

The Scientific Magic of Total Solar Eclipses

by Shadia Habbal and the Solar Wind Sherpas

Total solar eclipses continue to provide unique opportunities for probing the physical processes controlling the outer atmosphere of the Sun, also known as the solar corona. This is the beautiful halo that appears suddenly during totality when the moon completely blocks the bright solar disk. This is also the source region where the hot ionized plasma coupled with magnetic fields escape from our star in the form of a solar wind. It expands into interplanetary space, impinging on all objects in the Solar System, from planets, asteroids, comets to dust grains, and defining their immediate environment.  The solar wind can adversely impact our telecommunication systems when it entrails large bubbles exploding from the Sun at very high speeds and interacts with the magnetic environment of the Earth.

With the proliferation of space-based and ground-based telescopes observing the Sun, practically around the clock, one wonders why people go through the trouble of launching eclipse expeditions, which occur once a year at best, last for a few minutes, and when the observers are under the mercy of the weather. The answer is simple: it just so happens that what is visible to the eye, cameras and detectors from the ground, is not being exploited by existing observatories. The part of the solar radiation that lies in the visible wavelength range hosts a number of spectral lines (or colors) that enable us to probe the physics of the solar corona that no other instrument at present is capable of doing. One of the advantages of this emission is that it can be captured out to several solar radii from the solar surface, which is precisely where the expansion of the corona and solar wind is the most complex and decisive. To explore this region, one recurs to the use of filters that single out specific wavelengths through which the coronal emission can be analyzed.

Eclipse observations are technically challenging because of their short duration and the need to travel relatively ‘light’. In 2010, we discovered the Atik 314L cameras. They deemed to be ideal for imaging the corona with narrow bandpass filters, each probing a different temperature plasma in the corona. Not only were they lightweight, compact and very affordable, the image download time of less than 2 seconds, as well as the anti-blooming feature of the CCD chip, proved ideal for our applications. It was the first time that any scientific team was able to image the corona in seven different wavelengths simultaneously, almost surpassing what the Solar Dynamic Observatory (SDO) is boosting to achieve from space, albeit in the extreme ultraviolet. Although SDO provides unsurpassed temporal and spatial resolution, the extent of the emission is limited to 1/2 radius above the solar surface, which is not the case for the visible. By observing with multiple cameras and filters we were able to establish, unequivocally, the distribution of electron temperatures in the corona. This is shown in the attached figure, where red corresponds to Fe X, a spectral line formed by electrons at 1 million degrees, and green correspond to Fe XIV, a spectral line formed by electrons at 2 million degrees. Thus the co-existence of different temperature electrons is beautifully mapped over a distance range covering at least one radius above the solar surface. This is just one example of the scientific achievements enabled by the affordability and the technical superiority of the Atik 314L camera. The new model 414EX will be tested at the upcoming total solar eclipse of 20 March 2015. We are hoping for excellent observing conditions.

(The attached figure appeared as Figure 8(b) in the Astrophysical Journal, Vol 734:120, published in June 2010 by Habbal et al.)