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Astronomy - The Science of Astronomy

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    Study Guide Astronomy – The Science of Astronomy 1. Measurement Methods Astronomy deals with objects that are extremely large (like galaxies) and extremely small (like particles of light). Because of this, astronomers need special ways to measure and describe what they observe. To keep numbers clear and manageable, they use scientific notation , the metric system , and angular measurements . 1.1 Scien Ɵfi c Nota Ɵ on: Working with Very Big and Very Small Numbers In astronomy, numbers can quickly become too long to write easily. To solve this problem, astronomers use scientific notation , also called exponential notation . In scientific notation: • A number is written as a value between 1 and 10 • It is multiplied by a power of 10 For example: • 1,000 = 1 × 10³ • 1,000,000 = 1 × 10 ⁶ • 0.01 = 1 × 10 ⁻ ² This method makes it easier to compare, calculate, and understand very large or very small measurements.

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    Study Guide 1.2 The Metric System: A Common Language for Measurement Astronomers use the metric system , which is a decimal - based system used worldwide in science. It is simple because it is based on powers of ten. The basic metric units are: • Meter (m) for length • Kilogram (kg) for mass • Liter (L) for volume To describe larger or smaller measurements, prefixes are added to these units: • kilo - = thousand (1,000) • mega - = million (1,000,000) • giga - = billion (1,000,000,000) • centi - = one - hundredth (1/100) • milli - = one - thousandth (1/1,000) • micro - = one - millionth (1/1,000,000) For example: • A kilometer is 1,000 meters • A millimeter is 1/1,000 of a meter Astronomers use these units to measure everything from the thickness of a pencil to the distance across the universe.

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    Study Guide 1.3 Measuring the Sky: Understanding Angles Distances alone are not enough in astronomy. Astronomers also measure angles to describe the position and movement of objects in the sky. An angle is formed when two lines meet at a single point. • Angles are measured in degrees (°) • A right angle measures 90° • A complete circle measures 360° To make measurements more precise, astronomers divide degrees into smaller units: • 1 degree = 60 arcminutes ( ′ ) • 1 arcminute = 60 arcseconds ( ″ ) These small units are especially useful when measuring tiny objects in the sky, such as stars or the Moon.

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    Study Guide 1.4 Pu ƫ ng It All Together By using: • Scientific notation for very large and very small numbers • The metric system for consistent measurements • Angles and arc units to track positions in the sky astronomers can accurately describe the universe in a clear and organized way. These tools help turn complex observations into understandable measurements that scientists around the world can share and compare. 2. Basic Physics During the 16th and 17th centuries , scientists discovered important laws that describe how objects move. These laws help us explain and predict the motion of planets, moons, stars, and other objects in space . Two scientists played a major role in this discovery: Johannes Kepler and Isaac Newton .

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    Study Guide 2.1 Kepler’s Laws of Planetary Mo Ɵ on Johannes Kepler studied the motion of planets and proposed three laws that explain how planets move around the Sun. 2.2 Kepler’s First Law: The Law of Ellipses To understand the first law, we must first understand what an ellipse is. What Is an Ellipse? An ellipse is a stretched circle. It has: • Two fixed points called foci • A major axis (the longest diameter) • A minor axis (the shortest diameter) • A center , where the two axes intersect A special property of an ellipse is that the sum of the distances from any point on the ellipse to the two foci is constant .

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    Study Guide 2.3 Kepler’s First Law Explained Kepler’s First Law states: Each planet moves in an elliptical orbit, with the Sun located at one focus of the ellipse. The size of a planet’s orbit is described by the semi - major axis (a) , which is half the length of the major axis . This value is also the planet’s average distance from the Sun . Eccentricity: How Stretched Is the Orbit? The shape of an ellipse is described by its eccentricity (e) . • e = 0 → perfect circle • 0 < e < 1 → ellipse • e = 1 → straight line If the foci are close together , the ellipse looks more like a circle (small eccentricity). If the foci are far apart , the ellipse is more stretched (large eccentricity). Perihelion and Aphelion • Perihelion : the point where a planet is closest to the Sun o Distance = a(1 − e) • Aphelion : the point where a planet is farthest from the Sun o Distance = a(1 + e)

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