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Observing the Solar System
Observing the Solar System

...  8.4.c. Students know how to use astronomical units and light years as measures of distance between the sun, stars, and Earth.  8.4.d. Students know that stars are the source of light for all bright objects in outer space and that the Moon and planets shine by reflected sunlight, not by their own ...
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... example, section 35.2 is composed of seven paragraphs. Thus this section should be summarized in seven sentences. The first paragraph in section 35.2 could be summarized as follows: 35.2 Birth of the Solar System “ The Solar Nebula Theory, first proposed by Immanuel Kant and Pierre Simon Laplace in ...
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... Evidence of collisions: - cratered surfaces on objects of all sizes - high mass density of Mercury - extremely volatile-poor composition of the Moon - heavy bombardment until 700 My after the Moon was formed - the huge Herschel crater on Mimas - retrograde rotation of Uranus and Pluto - spin axis ti ...
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... He found that the brightest star in each galaxy had almost the same intrinsic brightness. When he knew how far away a galaxy was he looked at the red shift. When he knew the red shift he could calculate the velocity of the galaxy. He found a correlation between the distance from Earth and the veloci ...
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... Besides the nine planets and their moons, there are thousands of other smaller objects in our Solar System. One of which are small chunks of rocks called asteroids. The tiniest asteroids are less than a mile wide. The largest is over 600 miles wide. Small chunks of iron and rock that break away from ...
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... to rotate once on its axis. . (p. 465) Any object that orbits around another object in space. The moon is a natural satellite of Satellite the Earth. An artificial satellite is a device that is launched into orbit around the Earth or another planet. Artificial satellites are designed for many purpos ...
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... Saturn is the first planet known to have rings. The rings exist in a system. These rings are made of pieces of rock and ice. Scientists believe these particles came from shattered comets, asteroids, or moons. The particle sizes range from microscopic to as large as a house. Saturn has thousands of r ...
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Planets around Other Stars

... Reproduced below is a plot of observations of the radial velocity of the star 51 Pegasi, the first star discovered to have a planet. The observed velocity (in meters per second) is plotted vs. the time (in days) when the observation was made. The velocity of the star varies with time because the sta ...
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Definition of planet



The definition of planet, since the word was coined by the ancient Greeks, has included within its scope a wide range of celestial bodies. Greek astronomers employed the term asteres planetai (ἀστέρες πλανῆται), ""wandering stars"", for star-like objects which apparently moved over the sky. Over the millennia, the term has included a variety of different objects, from the Sun and the Moon to satellites and asteroids.By the end of the 19th century the word planet, though it had yet to be defined, had become a working term applied only to a small set of objects in the Solar System. After 1992, however, astronomers began to discover many additional objects beyond the orbit of Neptune, as well as hundreds of objects orbiting other stars. These discoveries not only increased the number of potential planets, but also expanded their variety and peculiarity. Some were nearly large enough to be stars, while others were smaller than Earth's moon. These discoveries challenged long-perceived notions of what a planet could be.The issue of a clear definition for planet came to a head in 2005 with the discovery of the trans-Neptunian object Eris, a body more massive than the smallest then-accepted planet, Pluto. In its 2006 response, the International Astronomical Union (IAU), recognised by astronomers as the world body responsible for resolving issues of nomenclature, released its decision on the matter. This definition, which applies only to the Solar System, states that a planet is a body that orbits the Sun, is massive enough for its own gravity to make it round, and has ""cleared its neighbourhood"" of smaller objects around its orbit. Under this new definition, Pluto and the other trans-Neptunian objects do not qualify as planets. The IAU's decision has not resolved all controversies, and while many scientists have accepted the definition, some in the astronomical community have rejected it outright.
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