Most of us who peer through our telescopes at the vast and awe-inspiring beauty of our universe do so at night. This makes a lot of sense as you are viewing distant objects with faint traces of light. But a nice compliment to your astronomical experience (one which most people ignore) is the daytime viewing of our sun.
Almost any refracting telescope can be used to safely view the sun, but you need to be properly prepared. Most telescope sets come with a simple eyepiece filter, but these should not be used. If you plan to take solar observations, you should invest a little money on quality solar filters.
But before you make your purchase, you should know about the differing types of filters (as well as their observational effects).
HYDROGEN-ALPHA FILTERS
H-alpha (or H-A) filters block all light except for the H-A wavelength. This type of filter allows you to view solar flares, prominences, surface details (such as granulation) and the corona. They are meant for use on refracting telescopes only. These filters are attached to the front of the telescope, as well as to the eyepiece. These filters must be used together, they cannot be used independently. The surface of the sun is rendered in an orange, almost reddish color with these filters. This allows you to view all of the action, with exception of occurrences which happen on the disk of the sun (these are normally heading toward the observer and become Doppler-shifted). Most quality filters however, will include a “tuner” (which fits between the filter and its adapter plate). This tuner lets you to change the passband of the filter, allowing you to possibly view these objects as well. The foremost producer of H-alpha filters is Coronado Instruments. In fact, besides producing solar filters, this company also manufactures dedicated solar telescopes. In addition to Coronado, companies such as Lunt Solar Systems and Solarscope Filters also provide quality H-alpha filter systems.
WHITE-LIGHT FILTERS
These durable, inexpensive filters reject over 99.9 percent of the sun’s spectrum, allowing you to view the sun in a yellowish-orange color. After attaching this lens to the front end of your telescope (refractors only), you will be able to view sunspots, convection-cell granulation, eclipses, and dimples caused by the Wilson Effect. An added advantage with this type of filter is that (with an extra attachment) you are able to take photographs of your observations. There are a few companies that produce white-light filters – Thousand Oaks Optical and Baader Planetarium produce the best. Actually, in addition to producing the normal filter type, Baader also produces a solar prism wedge which is said to produce the finest detailed white-light views available.
CALCIUM-K FILTERS
The Calcium-K filter acts much as an H-alpha filter does, but it filters out all light except for the Calcium-K spectral line. Since Calcium makes up only a small portion of the mass of the sun, the images you get from this type of filter shows you phenomena which are difficult to see. This type of filter allows you to detect coronal holes, as well as the ability to view chromospheric emissions created as calcium ions are swept through the magnetic fields. As a result of the filtering process, the sun can appear from neutral white, to varying shades of blue, and even purple under certain circumstances. This type of filter tends to be less expensive than Hydrogen-alpha filters. Coronado and Lunt (just as with the H-alpha types) are considered to be the best with this type of filter – as well as dedicated solar telescopes of this type. And just as with white-light filters, these allow you to take photographs of the images you view.
OTHER TYPES
If money is an issue, you might want to try the inexpensive Mylar and Polymer types of filters. Although the quality is not as good, they will still give you a natural yellow-orange image of the sun – allowing you to easily view solar eclipses.
Before you use your new filter, there are a few words of warning when viewing the sun.
* First, it is a good idea to remove or cover your finderscope; this prevents crosshair burnout and inadvertent eye damage.
* Next, ALWAYS install the solar filter before aiming it at the sun.
* You should generally aim it toward the sun using its shadow (just as you would a sundial), you should NEVER use the naked eye to manually align it.
* You should always visually inspect the filter for any scratches or pinholes before use. Although there is no real risk of eye damage, these abnormalities can distort the image. These scratches should be touched up (on the inside of the lens) by a fine point black felt-tipped marker.
There are several other means by which to view the sun if you so choose. As mentioned before, you can purchase a dedicated solar telescope. These models come in both H-alpha and Calcium-K models. These are quite expensive however, most people prefer to use filters with their existing telescopes. Another instrument you could use is the SUNSPOTTER. This instrument uses a series of mirrors to project the sun’s image onto a viewing screen. Through its magnification lenses, you are able to easily view sunspots and eclipses.
A cheap thing you can do (you might remember this from elementary school) is the PINHOLE CAMERA. This consists of two sheets of white paper, with a small hole punched in one of them. Using the full sheet as the viewing screen, you hold the piece of paper (with the hole) above to allow the light to shine through to the screen. By moving the piece of paper up and down, you will focus on the best image. What’s important to note here is that you’re not just viewing a dot of light. Because of the intensity of the sun, you are viewing an image of the sun itself (along with its sunspots).
You can also view images from specific solar telescope observatories online. Some websites – such as Mike Rushford’s robotic solar observatory (in Livermore, California) allow you to remotely control the telescope itself. These not only give you extraordinary images, but also provide you with valuable research data.
There are many ways to expand your astronomical experience, this is but one of them.
