The Sun in Halpha - September 2013



About the image…

Image title – The Sun in H-alpha.
Taken at – Instituto de Astrofisica de Canarias - Main headquarters (La Laguna, Tenerife – Spain).
Telescope Telescope Lunt solar H alpha 100 with bandwidth <0.7 Angstrom.
Instrument – Digital SLR.
Instrument – 800mm plus focal doubler; 1600mm.
Exposure –
400 stacked photos.
Image size 30' x 30'.
Images taken and reduced by –
Daniel López.
Text – Daniel López and Pablo Rodríguez-Gil.

H-alpha image of the Sun, our parent star, obtained with a 0.1-m solar telescope of the SolarLab project at the Astrophysics Institute of the Canary Islands (IAC) and a digital SLR camera. The Sun is a star of spectral type G2 located at an average distance of 149 600 000 km.

The 'photo stacking' technique was used to produce this month's AIM. 400 fast exposures were taken in less than 1 minute. Stacking them to produce a single image produces a significant improvement of signal over noise. Digital SLRs are not the most suitable equipment for solar photography. The Bayer matrix used to obtain colour images, together with a H-apha filter with a narrow bandwidth of < 0.7 Angstrom, work against image definition. However, by adding hundreds of images properly processed a result very similar to that obtained with a monochrome CCD camera can be achieved. This way the SLRs large CMOS sensors are an advantage because the entire solar disc fits in the frame, avoiding the need of mosaics. This also allows to make time lapses of the Sun by taking a stacked picture every minute is an easier way.

H-alpha imaging of the Sun provides a plethora of details. Apart from the intrinsic majesty of the Sun, these images are great to observe the characteristic solar protuberances.

The September AIM was taken from the IAC's headquarters in La Laguna, Tenerife, at ~600 m above sea level. This gives an idea of the quality of the Canary Islands sky, even at low altitude in populated areas.