Star date: 10:26:98

The Closest Star

There are around 400 billion stars in our galaxy, and perhaps 100 billion other galaxies. The number of stars in the known universe is almost staggering. But throughout most of the course of 2,000 years of the history of astronomy, we were never able to observe the surface of any of these stars, except one. Only in the last few yards have space borne telescopes and ground based telescopes equiped with adaptive optics been able to resolve detail on even the closest stars.

The one star we have been able to see the surface of for at least a few decades is, of course, the Sun. In ancient Greece, the Sun was first believed to be perhaps the size of a shield, and just barely higher than the mountains. This theory was largely dismissed by the realization that climing to the top of a mountain does not bring you any closer to the Sun. Next, it was believed that the Sun was maybe the size of a town, or perhaps a few dozen miles across, and just barely further than the Moon (how else would you explain eclipses?).

Democritus of Abdera was the first person we know of to argue that the Moon was much larger than the Peloponasia, which is about 1/3 the size of Greece. His answer was considered ridiculously large, and not worthy of consideration by many people of his time.

The first person to make any useful telescopic measurements of the Sun was Galileo (who did the first telescopic observations of many other objects as well). He was the first to identify sunspots, flares, and prominances. Galileo, in fact, went blind from viewing the Sun without using proper precautions.

This was not as trivial of a discovery as it might seem today. These discoveries were the first concrete evidence the human race had that the Sun, long thought to be perfect and unchanging, was not. For the first time, we had recorded imperfections on the Sun, which made us see the universe as much more like our dynamic, changing Earth.

The Sun is one of the only two objects which can be seen year round by people around the world. The other is, of course, the Moon. The Sun is, however, the only object in the sky which can be dangerous to view. This is why you must always use a proper filter when making telescopic observations of the Sun. The only safe types of solar filters fit over the front of a telescope, NEVER allowing sunlight to enter even a single lens.

There are two major designs of these, one made of mylar and another constructed of glass coated with aluminum or another metal. Also remember to cap the front of your finderscope. The image of the Sun magnified even modestly by a finderscope can be dangerous. Besides, you shouldn't need a finderscope to find the Sun! Also, never project a magnified image of the Sun onto a piece of paper. This is dangerous for both your eyesight and your telescope.

Line your telescope up easily on the Sun by finding moving your scope until it is projecting a round shadow on the ground. Sunspots appear as dark areas on the Sun, looking like ink blots against the yellow surface of the Sun. They are cooler than the surronding area, and thus appear black. In fact, they are still radiating most of their energy in the form of visible light, but are radiating less of it than the surronding medium, and appear black.

But what causes sunspots? It turns out that it has to due with the magnetic field of the Sun. The Sun rotates faster at the equator than it does at the poles This is known as differential rotation. Magnetic lines of force (like the familar lines formed by iron on a sheet of paper covering a bar magnet) form between the north and south poles of the Sun. These lines of force are then streched by the differential rotation of the Sun until they break. These then form sunspots, which always form in pairs, one of them rotating around the Sun north side first, and the other one rotating around the Sun south side first.

Next week, more on the Sun.

Clear skies, and good viewing.


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