by Robert Bullard

Created on: March 12, 2009

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

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