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Stardate: 09:21:97
The Sun without a doubt, the brightest object in the sky, is also the first astronomical object most of us see as children.
I am sure that at that tender age, we all gaze towards the Sun and wonder, "what that bright light is in the sky?" Perhaps it brings back quickly fading memories of birth, with rememberences of the first light we see (if we are born in a hospital) of the light above the delivery table.
Ancient people believed the stars were fixed in the sky, except that there were certain objects in the sky which seemed to move against the background stars. They would go on to name seven of them; the Sun and the Moon, Mercury, Venus, Mars, Jupiter, and Saturn.
It seems certain that the Sun was the first object which the ancients noticed moved against the backgrond of the so called "fixed stars". They became known by the Greek word for wanderer; "planet".
The most important thing to remember when viewing the Sun is to never use any kind of optical device such as a telescope or binoculars (or even the small finder telescope on a larger telescope) without a high quaility solar filter.
When you are selecting a solar filter, it is important that you only buy a type of solar filter which goes over the front of your telescope. In order not to destroy our telescope, you must filter out most of the light before it enters the telescope. Many inexpensive telescopes come with so called solar filters which fit into the eyepiece of your telescope. Never use this type of solar filter. The incredible heat generated by the light being magnified through your telescope will quickly melt the fittings for the optics, and could quickly destroy the optics themselves, not to mention your eyes!
Another dangerous type of solar filter is known as a Herschel lens. These look like a diagonal (the 90 degree adapter often found between a telescope and it's eyepiece), except that the back of it has a piece of glass rather than a mirror. The idea is that most of the light will pass through the glass, while reflecting only a small percentage up to the eyepiece for observation. It is true that most of the light passes through the glass, but it reflects up about one percent of the light into the eyepiece. These relect light for the same reason (known as Newtonian relection) that, under the right conditions, you can see your reflection as you look out a window. After magnification, this one percent, however, is far more light than your eye can safely handle.
Most good quality solar filters allow only about one hundredth of one percent of the light to pass through your telescope and into your eye. The highest safe transmission is about one tenth of one percent. There are two basic designs of good, safe, high quality solar filters. There are filters made of mylar, such as those produced by Celestron, but these turn the image an unnatural shade of blue. This can, of course, be corrected by adding a # 23 or #25 red color filter. The other type of good solar filter are glass, and are coated with aluminum. Many of these are made by a company known as Thousands Oak Optical, who frequently advertise in Astronomy magazines such as Sky and Telescope and the monthly magazine Astronomy.
Another important thing to keep in mind once you do have a good quality solar filter, is to never make the mistake of looking through the unfiltered finderscope. After all, looking through a low power telescope at the Sun was exactly how Galileo himself went blind!
Two of the greatest treats to look at through a telescope on the Sun are cool, dark regions known as sunspots, and solar flares exploding from the side of the Sun with the force of millions of hydrogen bombs. It is these objects we shall look at next week, along with the elusive sub-atomic particle the nuetronio, which is the form of most of the Sun's energy. We will also discuss why the Sun is yellow, and why there is reason to believe that the Sun may have already died; perhaps even a million years ago!
Clear skies, and good viewing.
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