Astronomy - The Science of Astronomy - Quick Guides

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Study GuideAstronomy–The Science of Astronomy1. Measurement MethodsAstronomy deals with objects that areextremely large(like galaxies) andextremely small(likeparticles of light). Because of this, astronomers need special ways to measure and describe what theyobserve. To keep numbers clear and manageable, they usescientific notation, themetric system,andangular measurements.1.1ScienƟfic NotaƟon: Working with Very Big and Very Small NumbersIn astronomy, numbers can quickly become too long to write easily. To solve this problem,astronomers usescientific notation, also calledexponential notation.In scientific notation:•A number is written as a valuebetween 1 and 10•It is multiplied by apower of 10For example:•1,000 = 1 × 10³•1,000,000 = 1 × 10⁶•0.01 = 1 × 10⁻²This method makes it easier to compare, calculate, and understand very large or very smallmeasurements.

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Study Guide1.2The Metric System: A Common Language for MeasurementAstronomers use themetric system, which is a decimal-based system used worldwide in science. Itis 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 volumeTo 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:•Akilometeris 1,000 meters•Amillimeteris 1/1,000 of a meterAstronomers use these units to measure everything from the thickness of a pencil to the distanceacross the universe.

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Study Guide1.3Measuring the Sky: Understanding AnglesDistances alone are not enough in astronomy. Astronomers also measureanglesto describe theposition and movementof objects in the sky.Anangleis formed when two lines meet at a single point.•Angles are measured indegrees (°)•Aright anglemeasures90°•Acomplete circlemeasures360°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 theMoon.

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Study Guide1.4Puƫng It All TogetherBy using:•Scientific notationfor very large and very small numbers•Themetric systemfor consistent measurements•Angles and arc unitsto track positions in the skyastronomers can accurately describe the universe in a clear and organized way. These tools help turncomplex observations into understandable measurements that scientists around the world can shareand compare.2. Basic PhysicsDuring the16th and 17th centuries, scientists discovered important laws that describe how objectsmove. These laws help usexplain and predict the motion of planets, moons, stars, and otherobjects in space. Two scientists played a major role in this discovery:Johannes KeplerandIsaacNewton.

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Study Guide2.1Kepler’s Laws of Planetary MoƟonJohannes Kepler studied the motion of planets and proposedthree lawsthat explain how planetsmove around the Sun.2.2Kepler’s First Law: The Law of EllipsesTo understand the first law, we must first understand what anellipseis.What Is an Ellipse?Anellipseis a stretched circle. It has:•Two fixed pointscalledfoci•Amajor axis(the longest diameter)•Aminor axis(the shortest diameter)•Acenter, where the two axes intersectA special property of an ellipse is that thesum of the distances from any point on the ellipse tothe two foci is constant.

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Study Guide2.3Kepler’s First Law ExplainedKepler’s First Law states:Each planet moves in an elliptical orbit, with the Sun located at one focus of the ellipse.Thesizeof a planet’s orbit is described by thesemi-major axis (a), which ishalf the length of themajor axis.This value is also the planet’saverage distance from the Sun.Eccentricity: How Stretched Is the Orbit?Theshapeof an ellipse is described by itseccentricity (e).•e = 0→perfect circle•0 < e < 1→ellipse•e = 1→straight lineIf thefoci are close together, the ellipse looks more like a circle (small eccentricity).If thefoci are far apart, the ellipse is more stretched (large eccentricity).Perihelion and Aphelion•Perihelion: the point where a planet isclosest to the SunoDistance =a(1−e)•Aphelion: the point where a planet isfarthest from the SunoDistance =a(1 + e)

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