Astronomy term paper

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“This world has a diameter of only 3,140 miles, and is the smallest of the old planets. Pursuing our journey, at a distance of 68,000,000 miles from the sun, we cross the orbit of the planet Venus. Her magnitude is nearly equal to that of the earth. Her diameter is 7,700 miles, and the length of her year is nearly 225 of our days. The next planet is the earth, whose mean distance from the sun is 95,000,000 miles. The peculiarities which mark its movements and those of its satellite are well known. Leaving the earth, and continuing journey outward, one may cross the orbit of Mars, at a mean distance from the sun of 142,000,000 miles. This planet is 4,100 miles in diameter, and performs its revolution around the sun in about 687 days, in an orbit but little inclined to the plane of the ecliptic. Its features are more nearly like those of the earth than any other planet. Beyond the orbit of Mars, and at a mean distance from the sun of about 250,000,000 miles, one can encounter a group of small planets, eight in number, presenting an anomaly in the system, and entirely different from anything elsewhere to be found. These little planets are called asteroids. Their orbits are, in general, more eccentric, and more inclined to be ecliptic, than those of the other planets; but the most remarkable fact is this, that their orbits are so nearly equal in size that, when projected on a common plane, they are not enclosed the one within the other, but actually cross each other.”
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“The peculiar importance of Kirchhoff's discovery to astronomy becomes obvious if one considers the position in which we stand to the heavenly bodies. Gravitation and the laws of our being do not permit us to leave the earth; it is, therefore, by means of light alone that we can obtain any knowledge of the grand array of worlds which surround us in space. The starlit heaven is the only chart of the universe we have, and in it each twinkling point is the sign of an immensely vast though distant region of activity. Hitherto the light from the heavenly bodies, even when collected by the largest telescope, has conveyed to us but very meager information, and in some cases only of their form, their size, and their color. The discovery of Kirchhoff enables us to interpret symbols and indications hidden within the light itself, which furnish trustworthy information of the chemical, and also to some extent of the physical, condition of the excessively remote bodies from which the light has emanated. Astronomy is indebted to Newton for the knowledge that the beautiful tints of the rainbow are the common and necessary ingredients of ordinary light. He found that when white light is made to pass through a prism of glass it is decomposed into the beautiful colors which are seen in the rainbow. These colors when in this way separated from each other form the spectrum of the light. Let this white plate represent the transverse section of a beam of white light traveling toward you. Let now a prism be interposed in its path. The beam of white light is not turned aside as a whole, but the colored lights composing it are deflected differently, each in proportion to the rapidity.”
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““…there might be another star or another close pair. It is easy to understand why all the components of a multiple system cannot have comparable mutual separations— such systems are known to be unstable unless the number of components is very large. Rich and very rich systems do exist, and they are known as clusters of stars and galaxies. Various binaries may differ enormously in their extent. There are many pairs of stars touching each other. These are the contact systems of the W Ursae Majoris or SV Centauri type. A whole contact binary is only slightly larger than the sun, some 3 x 10 11 cm in diameter. At the other extreme there is the nearby triple system, a Centauri ABC. The component a Centauri C, also known as Proxima Centauri, is a distant companion to a binary, a Centauri AB. The separation between components A and B is 3 x 10 14 cm, whereas component C is about 10 17 cm away from A and B.

Various binaries populate fairly uniformly a whole range of separations from about 3 x 10" to 3 × 10 17 cm, which corresponds to orbital periods of 1 to 10 9 days (that is, up to about 3 million years). Roughly 10 percent of all stars are binaries with orbital periods between 1 and 10 days, another 10 percent have orbital periods between 10 and 100 days, and so on. There is a rapid cutoff in the number of systems with separations larger than about 3 x 10 17 cm, most likely due to gravitational perturbations caused by other stars belonging to our galaxy and randomly passing by. The average distance between separate stars or stellar systems in the solar neighborhood is about 4 x 10 18 cm.”
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