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16 October 2006
16 October 2006

... Other isotopes of uranium are not found on earth, although some have half-lives in the millions of years. • Elements heavier than uranium do not occur naturally at all on earth. The longest-lived example is an isotope of plutonium with a half-life of 80 million years. • Of the hundreds of isotopes w ...
Unit 7 Astronomy
Unit 7 Astronomy

... and that sustains life on Earth, being the source of ____________________________________________ heat and light. Dark, irregular spots that are cooler than a. sunspots: ___________________________ the surrounding areas on the Sun. ___________________________________________ ...
Sample Final - IUPUI Physics
Sample Final - IUPUI Physics

... D) nothing 48) Which of the following stars will undergo a supernova at the end of its lifetime? A) a star the mass of the sun B) a star at least 10 times the mass of the sun C) a star less than half the mass of the sun D) all of these stars will undergo a supernova at the end of their lifetimes 51) ...
Part 1
Part 1

... (A) the change in Earth’s distance from the Sun. (B) the Sun’s changing brightness during the sunspot cycle. (C) one side of the Sun being cooler than the other. (D) Moon’s shadow on Earth. (E) the Earth’s rotation axis being tipped so that first one hemisphere and then the other receives sunlight m ...
What would life on other planets be like?
What would life on other planets be like?

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Review of "Man`s Place in Nature" by Alfred Russel Wallace
Review of "Man`s Place in Nature" by Alfred Russel Wallace

... therefore in all probability in the center of the whole material universe. This conclusion no doubt is a startling one, and all kinds of objections will be made against it, yet I am not acquainted with any great inductive result of modern science that has been arrived at so gradually, so legitimatel ...
Venus is a rocky planet very similar in size and surface gravity to
Venus is a rocky planet very similar in size and surface gravity to

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FREE Sample Here

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The Motions of Celestial Bodies, and Newton`s Laws of Motion

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Stars and Galaxies

FREE Sample Here
FREE Sample Here

... A. East to west motion of the Sun over many successive nights. B. East to west motion of the Moon relative to the stars over many successive nights. C. Occasional east to west motion of the planets relative to the stars over many successive nights. D. Occasional west to east motion of the planets re ...
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Are we alone? - School of Physics

... the sky several metres away or more, it is impossible to tell how far away it is, or how big.” Is it: •A fire fly—5 metres away? •A balloon —500 metres away? •An aircraft —5 km away? •Venus —50 million km away? ...
The Sun to the Earth - Stanford Solar Center
The Sun to the Earth - Stanford Solar Center

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LETTERS A giant planet orbiting the ‘extreme horizontal

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Chapter 27 Stars and Galaxies

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... Mars has two small moons. A probe found a giant _______________ sea of water there and scientists believe there may be some kind of microbes living in the soil. These four planets - Mercury, Venus, Earth and Mars are known as the inner planets. Next comes a big gap called the _______________ _______ ...
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Unit 6--Astronomy

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Introduction to cosmology I

... Law 1 Every body continues in its state of rest, or uniform motion in a straight line, unless compelleed to change by forces acting on it Law 2: The change in motion is proportional to the force impressed, and in the direction of the force Law 3: To every action there is always an equal and opposite ...
History Test Review Answers - School District of La Crosse
History Test Review Answers - School District of La Crosse

... 11.The__EGYPTIAN____________culture based their planting of the crops on the rising of the star Sirius, because the Nile would flood about this time. 12. ___HELIOCENTRIC__________model suggest the earth is the center of the solar system 13. The problem with ptolemy's model is he used imaginary ___C ...
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Formation of the Solar System Chapter 8

... The idea that the solar system was born from the collapse of a cloud of dust and gas for proposed by Immanuel Kant (1755) and by Pierre Simon Laplace 40 years later. During the first part of the 20th century, some proposed that the solar system was the result of a near collision of the Sun with anot ...
Place in Space
Place in Space

... Q1:The fastest thing that we know of is light which travels at a speed of 186,000 miles or 300,000 kilometres per second in empty space. Light can travel about seven times around Earth in one second. Astronomers use the speed of light to measure how far away things are in space. They use light years ...
Lecture 09a: Habitable zones - Sierra College Astronomy Home Page
Lecture 09a: Habitable zones - Sierra College Astronomy Home Page

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Rare Earth hypothesis



In planetary astronomy and astrobiology, the Rare Earth Hypothesis argues that the origin of life and the evolution of biological complexity such as sexually reproducing, multicellular organisms on Earth (and, subsequently, human intelligence) required an improbable combination of astrophysical and geological events and circumstances. The hypothesis argues that complex extraterrestrial life is a very improbable phenomenon and likely to be extremely rare. The term ""Rare Earth"" originates from Rare Earth: Why Complex Life Is Uncommon in the Universe (2000), a book by Peter Ward, a geologist and paleontologist, and Donald E. Brownlee, an astronomer and astrobiologist, both faculty members at the University of Washington.An alternative view point was argued by Carl Sagan and Frank Drake, among others. It holds that Earth is a typical rocky planet in a typical planetary system, located in a non-exceptional region of a common barred-spiral galaxy. Given the principle of mediocrity (also called the Copernican principle), it is probable that the universe teems with complex life. Ward and Brownlee argue to the contrary: that planets, planetary systems, and galactic regions that are as friendly to complex life as are the Earth, the Solar System, and our region of the Milky Way are very rare.
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