Sky's Up Global Astronomy Magazine Volume II (April 2021) | Page 54

Solar surface features and size of solar system objects against them .
COURTESY OF Debasis Sarkar and Janmejoy Sarkar . ( Sky Watchers Association of North Bengal ) narrower bandpass of even 0.5 Å . Understandably , images formed through an H-Alpha system is essentially monochromatic . Only one colour is there which is predominantly red because of its frequency 6562.8 Å , very close to that of red ( 7000 Å ). Thus , to make them visually pleasing the images are usually false colored instead of keeping monochromatic or black and white .
How to use H-Alpha ? Basic usage of this goes like common refractor telescopes that can be used for either live viewing or photographing . But tuning an H alpha system is a tedious job that demands deep patience . Attachment of a second etalon sharpens the image , but at the cost of brightness and by making it more complicated to handle . Eventually , viewing becomes tougher with an H-Alpha system with a second stack of etalon . As it is with all other optics , the quick movement of the Sun within the field of vision is a major hurdle . A properly polar aligned RA axis motorized mount can keep the system in sync with Earth ’ s movement and thus freeze the Sun ’ s movement in the viewing field .
How to do photography with H-Alpha ? There are different techniques to attach a camera to an H-Alpha system . It can be “ prime focus ” style where the eyepiece of H-Alpha system and
28 camera lens are not used . The main objective of the system works as the camera lens while camera body takes the photo . Or “ afocal ” style where the image formed by the objective is thrown by the eyepiece on the camera lens . Eyepiece projection is also common to “ project ” the image formed by objective through the eyepiece directly on film or electronic image sensing panel inside the camera without its own lens . But whatever be the attachment pattern , filament and other surface details demand grossly different exposure settings of an H-Alpha camera set-up . Thus , multiple shots with different properly calculated exposures are taken . Then specialized image post processing techniques are adopted to blend those images to develop an image with proper replication of surface details consisting of different features .
Is it available ? Now many companies offer H-Alpha systems at affordable price ranging from USD 600 to USD 4000 . But high import duty or shipping cost are factors to escalate its price in India . As it is with almost everything else , ease of using them or other features of different models of different brands vary with the price . And so for the output quality too . Here , in this article , images taken with moderately sized system only have been included .
Fascinating solar features observed through H-Alpha
Prominence : Large , bright , gaseous tongues extending outward from the Sun ’ s surface . Anchored to the Sun ’ s surface in the photosphere , prominences extend outwards into the Sun ’ s corona . Solar filaments : These are dark lines or curves on solar surface . Filaments are actually prominences seen from different perspective . These appear dark over the background of the much brighter solar surface . Sunspots : Dark spots on the solar surface . These are cooler areas compared to its surrounding . Solar Flares : These are sudden explosions of energy due to tangling , crossing or reorganizing of magnetic field lines near sunspots . Solar granulation : Grainy feature visible on the surface of the Sun . Thermal currents in the thermal columns causes formation of granulation .