Astronomy 101 week one notes
Astronomy 101 week one notes ASTR 101
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This 5 page Class Notes was uploaded by Breanab on Saturday January 9, 2016. The Class Notes belongs to ASTR 101 at University of New Mexico taught by Trace Tessier in Spring 2016. Since its upload, it has received 24 views. For similar materials see Introduction to Astronomy in Astronomy at University of New Mexico.
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Date Created: 01/09/16
Astronomy 101 lecture one Kepler’s Laws • What are the shapes and important properties of the planetary orbits? o They are elliptical § Some times the orbit is closer and others its farther away • How does the speed of a planet vary as it orbits the sun? o As the planet moves closer to the sun, its orbit speeds up • How does the period of a planets orbit depend on its distance form the sun? o It grows longer the further the planet is from the sun Tycho Brahe • Collected vast amounts of astronomical data (positions of different bodies at certain times) without a telescope • Had a gold nose and a moose that couldn’t hold his liquor Kepler (1571-1630) • Used Tycho Brahe’s precise data on apparent planet motions and relative distances • Deduced three laws of planetary motion • Took him the last 30 years of his life Kepler’s first law • The orbits of the planets are elliptical (not circular) with the sun at one focus of the ellipse • ‘a’ is the semi major axis, the average distance between the sun and planet • ‘e’ is how much it deviates • a(1-e) Kepler’s second law • A line connecting the sun and a planet sweeps out equal areas in equal times, aka planets move faster when closer to the sun Kepler’s third law • The square of a planets orbital period is proportional to the cube of its semi major axis. Aka the further the planet is from the sun the longer the period Newton (1642-1727) • Newton’s laws are fundamental principles that govern the motions of all astronomical bodies • The natural state of motion of a body with no forces action on it is constantly at rest Newton’s first law of motion • Every object continues in a state of rest or a state of uniform motion in a straight line unless acted on by a force Inertia • Resistance to change in motion of object – is related to its mass Newton’s second law (f=ma) • When a force, F, acts on an object with a mass, m, it produces an acceleration , a, equal to the force divided by the mass (a=f/m) • Acceleration is a change in velocity or a change in direction of velocity • Newton’s laws classify objects as accelerating or non-accelerating, not as moving or stationary. Newton’s third law of motion • To every action there is an equal and opposite reaction • or when one object exerts a force on a second object, the second exerts an equal and opposite force on first what force governs the motions of astronomical objects, and what factors determine how strong the force is? • Gravity and mass Newton’s law of gravity • For two objects of mass m1 and m2, separated by a distance R, the force of their gravitational attraction is given by F= (Gm1m2)/R^2 • Weight is the gravitational force between the earth and the object • G is the gravitational constant 6.67384x10^-11 m^3 kg^-1 s^-2 Gravitational force • The gravitational force is always attractive • The strength of the attraction decreases with increasing distance Gravity and orbits • Throwing an object fast enough will put the object into orbit, neglecting air resistance • Moon is continually falling towards the earth in its orbit, gravity vs. inertia • Action- Reaction Correction to Kepler’s third law • Earth and sun actually rotate about their common center of mass • Corresponds to a point inside the sun • Used to detect extra solar planets 1/9/16 12:51 PM 1/9/16 12:51 PM
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