Our nearest star, the Sun, is the brightest object in the sky and amazingly dynamic. This makes solar observing exciting and readily accessible from a White Zone location.
Safety First
The sun is so bright that we must take great care to observe safely. Most importantly, NEVER look directly at the Sun, with your naked eye or through an unfiltered instrument, as this can cause immediate and permanent blindness.
Because of the care needed while solar observing, I would recommend starting first with lunar observing. Once you are ready to move on to solar observing, read on!
What to Look Out For
The Sun’s Structure
Above is a diagram illustrating the basic structure of the Sun.
- Core – Innermost 20-25% of the Sun’s radius. Temperature and pressure sufficient for nuclear fusion to occur. Here, hydrogen fuses into helium, releasing energy.
- Radiative zone – Between about 20-25% of the radius, and 70% of the radius, energy transfer occurs by means of radiation (photons) rather than by convection.
- Convective zone – Between about 70% of the Sun’s radius and a point close to the visible surface, the Sun is cool and diffuse enough for convection to occur, and this becomes the primary means of outward heat transfer.
- Photosphere – Deepest part of the Sun we can directly observe with visible light.
- Atmosphere – A gaseous ‘halo’ surrounding the Sun, comprising the chromosphere, solar transition region, corona and heliosphere. The heliosphere extends far beyond the orbit of Pluto. Hence, we do live within the atmosphere of the Sun!
Observable Features
The image below identifies some features that you can observe with the right eye protection and equipment.
Solar Observing Techniques and Equipment
(Almost) Naked Eye Observing
The sun is close enough that we can see some interesting features with our well-protected naked eyes. These include eclipses and sun spots. In fact, sunspots are detectable when looking at the sun through fog or cloud and were first recorded by the Chinese around 800 B.C.
Solar Viewing Glasses
These glasses are special eye-wear that allow direct observation of the sun. Normal sunglasses do not block enough of the sun’s direct rays to be safe.
When purchasing solar viewing glasses, buy from a reputable retailer and make sure the glasses are ISO 12312-2 certified (they will have a logo printed on them). Solar viewing glasses must allow at most 0.00032% of the sun’s rays to pass to comply with the standard.
Before use, you should ensure that the film is not punctured or creased.
Pinhole Viewer
Another simple and safe way to observe the sun is to build a pinhole viewer. You can find some instructions on building one on this National Geographic page.
Observing with Optical Aids
We can observe more details and finer features of the Sun using optical aids like telescopes. Of course, we must properly filter these optical aids, too. Filters must cover the full aperture of the instrument and must be secure so that they don’t accidentally get knocked or blown off. Do supervise young children as they are curious and may pull off the filter while someone is using the instrument, with dire results. Personally, I prefer to use a camera attached to the instrument to minimise risk – at worst, the camera sensor gets destroyed instead of someone’s vision.
White Light Filters
White light filters pass the whole visible spectrum of light but transmit only a safe fraction of it. Solar filters tend to look like mirrors because so they reflect the bulk of the light.
White light filters make it possible to observe the photosphere or “surface” of the sun, where most of the light is generated. This is also where sunspots occur and makes for exciting viewing. The granulation (texture) of the surface of the Sun can also be seen. The granules are caused by convection currents of plasma in the convective zone of the Sun.
Hydrogen-Alpha Narrowband Filters
Quite the opposite of white light filters, narrowband filters transmit only a very specific wavelength of light. Hydrogen-Alpha filters are among the most common of narrowband filters for solar observing (the Sun is mostly made up of hydrogen which emits light at this wavelength). The bandpass of these filters center around 656.3nm wavelength and typically are only 0.3-0.7Å wide. Other narrowband filters like Calcium K-Line filters enable us to observe different features of the Sun.
This very narrow bandpass allow us to observe even more features, including filaments and prominences, which are impossible to observe in white light.
Narrowband filters are expensive, hence, I would suggest starting first with white light filters until you have had a chance to try observing with narrowband filters.