Astronomy & Astrology - Astronomy Introduction & Index

Astronomy: Introduction & Index

II Amateur Astronomy
III How Astronomers Work	A. Observation	1. Optical Astronomy
		2. Gamma-Ray and X-Ray Astronomy
		3. Ultraviolet Astronomy
		4. Infrared Astronomy
		5. Radio Astronomy
		6. Study of Other Emissions
	B. Analysis and Theory
IV Earth's Night Sky	A. Earth's Relative Motion	1. Night, Day, and Seasons
		2. Phases of the Moon
		3. Eclipses
	B. Meteors
	C. Mapping the Sky	1. The Constellations
		2. Coordinate Systems
V The Solar System	A. Objects in Our Solar System	1. Planets and Their Satellites
		2. Comets and Asteroids
		3. The Sun
	B. Studying the Solar System
	C. Solar System Formation
	D. Detecting Other Solar Systems
VI Stars	A. Kinds of Stars	1. Main-Sequence Stars
		2. Giant and Supergiant Stars
		3. White Dwarf Stars
		4. Variable Stars
		5. Novas
		6. Supernovas
		7. Neutron Stars and Pulsars
		8. Black Holes
	B. Star Locations
	C. Starlight
VII Galaxies	A. The Milky Way
	B. Characteristics of Galaxies	1. Interstellar Matter
		2. Galactic Black Holes
	C. Types of Galaxies	1. Spiral
		2. Elliptical
		3. Irregular
	D. Movement of Galaxies	Hubble's law
VIII The Universe

I. Introduction

Astronomy, study of the universe and the celestial bodies, gas, and dust within it. Astronomy includes observations and theories about the solar system, the stars, the galaxies, and the general structure of space. Astronomy also includes cosmology, the study of the universe and its past and future. People who study astronomy are called astronomers, and they use a wide variety of methods to perform their research. These methods usually involve ideas of physics, so most astronomers are also astrophysicists, and the terms astronomer and astrophysicist are basically identical. Some areas of astronomy also use techniques of chemistry, geology, and biology.

Astronomy is the oldest science, dating back thousands of years to when primitive people noticed objects in the sky overhead and watched the way the objects moved. Advertisement In ancient Egypt, the visibility of certain stars for the first time each year marked the onset of the seasonal flood, an important event for agriculture. In 17th-century England, astronomy provided methods of keeping track of time that were especially useful for accurate navigation. Astronomy has a long tradition of practical results, such as our current understanding of the stars, day and night, the seasons, and the phases of the Moon. Much of today's research in astronomy does not address immediate practical problems. Instead, it involves basic research to satisfy our curiosity about the universe and the objects in it. One day such knowledge may well be of practical use to humans.