Astronomy 100Lxg Midterm 1 Key Ideas

# Astronomy 100Lxg Midterm 1 Key Ideas - Key Ideas Chapter 1...

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Key Ideas Chapter 1: Astronomy, Science and the Nature of the Universe – The universe is comprehensible. The scientific method is a procedure for formulating hypotheses about the universe. These are tested by observation or experimentation in order to build consistent models or theories that accurately describe phenomena in nature. Observations of the heavens have helped scientists discover some of the fundamental laws of physics. The laws of physics are in turn used by astronomers to interpret their observations. The solar system – Exploration of the planets provides information about the origin and evolution of the solar system, as well as the history and resources of Earth. Stars and Nebulae - Studying the stars and nebulae helps us learn about the origin and history of the sun and the solar system. Galaxies - Observations of galaxies tell us about the origin and history of the universe. Angular Measure - Astronomers use angles to denote the positions and sizes of objects in the sky. The size of an angle is measured in degrees, arc minutes, and arc seconds. Powers-of-Ten Notation is a convenient shorthand system for writing numbers. It allows very large and very small numbers to be expressed in a compact form. Units of Distance – A variety of distance units are used by astronomers. These include the astronomical unit (the average distance from Earth to the Sun), the light-year (the distance that light travels in one year), and the parsec. Chapter 2: Constellations and the Celestial Sphere – It is convenient to imagine the stars fixed to the celestial sphere with the Earth at its center. The surface of the celestial sphere is divided into 88 regions called constellations. Diurnal (Daily) Motion of the Celestial Sphere – The celestial sphere appears to rotate around the Earth once in each 24-hour period. In fact, it is actually the Earth that is rotating. The poles and equator of the celestial sphere are determined by extending the axis of rotation and the equatorial plane of the Earth out to the celestial sphere. The positions of objects on the celestial sphere are described by specifying their right ascension (in time units) and declination (in angular measure.) Season and the Titl of the Earth’s Axis – The earth’s axis of rotation is titled at an angle of about 23.5 degrees from the perpendicular to the plane of the Earth’s orbit. The

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seasons are caused by the tilt of the Earth’s axis. Over the course of a year, the Sun appears to move around the celestial sphere along a path called the ecliptic. The ecliptic is inclined to the celestial equator by about 23.5 degrees. The ecliptic crosses the celestial equator at two points in the sky, the vernal and autumnal equinoxes. The northernmost point that the Sun reaches on the celestial sphere is the Summer Solstice, and the southernmost point is the Winter Solstice.
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