SOLAR OBSERVING & IMAGING
With today’s filter technology, it is easy to convert your night time regular telescope in to a safe and effective solar observation instrument. A variety of choices exists to pre filter the huge amount of light entering your instrument from the sun. Whichever choice you make you should be aware that for safe visual observing, the filter should reduce the incoming light by 99.9% or a factor of 1/1000 of the raw sunlight. There a several different ways to do this but in the last ten years two types of filters are the most popular and effective ways to observe the sun in a safe manner.
Glass pre-filter:
Most natural coloration of image usually a warm yellow
Constructed of a plane parallel optical grade glass coated with a nickel-steel compound in a vacuum chamber.
For larger apertures (greater than 4 inch) it yields a smooth highly detailed image of sunspots, faculae and plages.
Mylar film (Baader Film):
A European product consisting of multi layered mylar films that yield a bright white light image with very good resolution.
Usually works best in smaller scopes (4 inch or less) or in an off-axis mask for larger scopes especially large Newtonians and Dobsonians.
The key element is to place a filter before the objective or any other element in the optical train in order to prevent heat from entering the instrument especially in compound and refractor telescopes with closed tubes.
Under no circumstances use an internal sun filter that fits on an eyepiece as supplied with older imported scopes and as these sit right at the point of highest heat and will crack sending a laser like beam of concentrated light into your eye instantly destroying your retina and causing permanent blindness.
If you have any doubt about the power of the sun through a telescope, point your scope at the sun with no eyepiece in the holder and place a sheet of paper at the focus, it should smolder and burst into flame almost immediately.
What can be seen?
At first the sun appears fairly smooth when seen through a telescope with perhaps a few dark spots. Closer examination will reveal that the spots themselves are usually composed of a complex series of two or more spot structures, each surrounded by a penumbra or lighter region. On days when the atmosphere is relatively quiet, great detail can be discerned with each of these sunspot groupings. Filamentary structure and bright bridges across the dark umbra can be discerned, sometimes if you are very fortunate, you will see a momentary flare or brightening in these areas…a solar flare or expulsion of material in progress. Faculae are whitish patches seen surrounding active areas especially toward the solar limb. Contrast on the Sun is observation of areas of different temperatures. Pores are small black dark areas without structure like sunspots. Granulation is tiny fine grain structure visible in good to excellent seeing.
One of the biggest obstacles to good resolution in solar observing is the state of the atmosphere. It is usually a good idea to observe fairly early in the day before the air has had a chance to heat up and form turbulent cells that will reduce resolution and the perception of fine detail. Larger apertures can be used to resolve finer detail. I usually like to observe before noon. If observing in warm conditions smaller apertures (60 – 100mm) will normally be more effective.
Recording your observations:
Recording what you see is an excellent way to maintain a record over the years of the solar cycles for your own edification and enjoyment.
Drawing either whole disk drawings or active region detail drawings is a great way to see more as you search out each detail in order to record it. A combination of both with the whole disk drawing with the details plotted at their solar coordinate positions allows a continuous record over the years of solar activity and rotations as the solar cycles wax and wane. Counting of sunspots is an activity which many enjoy and an opportunity to contribute to real science.
Film photography:
While not as convenient as digital photography, worthwhile work can be done using color and black & white films in the 100 to 400 iso speed categories, remembering that the faster the film the coarser the grain resulting in lower resolutions. For daily or weekly shooting, shoot lots of pictures at varying exposures because you are going to throw away a lot of pictures. Exposures are generally fast and either prime focus or eyepiece projection techniques are used with a single lens reflex 35mm camera with removable lenses.
Digital imaging:
Two methods are worthwhile and they are digital cameras either SLR with the same methods as for film cameras or fixed lens models using afocal projection with an eyepiece…in the 30 to 40mm range for whole disk to close-up zoom-ins of sunspot details.
Either auto setting can be used for acceptable exposures or the camera can be set on manual settings and the iso, exposure and sensitivity can be experimented with, remember to shoot in an uncompressed mode such as tiff or raw to record the most detail.
If exposure is over 1/1000 sec, consider using a neutral density filter either ND25(25% transmission) or an ND13 (13% transmission) to lower exposure time.
The other method is webcam/computer which works very well for individual sunspots.
Which ever method you prefer, you will shoot lots of frames and throw away all but the best shots. Experiment, combine imaging methods and when the sun is active you will find that you have more than enough to do and wonder at a spectacle that you will never tire of.
Baader Solar Continuum Filter:
A new filter from Baader Planetarium that is extremely narrowband, (540nm) that allows views and images of the solar surface features and incredible sunspot detail.
Coronado Personal Solar Telescope:
The PST allows viewing of the Solar disk in Hydrogen Alpha light to facilitate observation of prominences, plages, flares and active regions of the chromosphere as opposed to white light observing which shows the photosphere. When nothing is visible in white light, there is still considerable activity in H-A that can be seen, especialy filaments and prominences. One is able to enjoy the sight of huge amounts of material being flung into space and even the magnetic loops become visible from the materail trapped within. If the PST is piggy backed onto your regular scope, you can enjoy both views as well as share it with others.
