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Why We Have Seasons? * tilt of the earth’s rotation axis with respect to the ecliptic (combined with Earth’s revolution around the Sun) * ARNT caused by the changing distance from the Earth to the Sun that results from the shape of Earth’s orbit. – axis is tilted –revolve around the sun The Ecliptic - Straight path on the celestial sphere the sun traces - A plane (described by earths path around the sun)creates 2(plane rep. earths orbit) Kepler (Johannes) – favored the Copernican Model - used Tycho’s data for the motion of mars to figure out the nature of planetary orbits - model was precice and did not require use of epicycles (<- no such thing as) - laws describe orbital shapes, changing speeds and the lengths of planetary years - Law #1~ orbits of planets are ellipses with sun at 2 of the focal points o Explains perihelion and aphelion - Law #2~ (line joining the) Planets sweep out equal areas in equal amounts of time o Explains apparent variable motion of the sun - Law #3 ~ square of a planet’s sidereal period around the sun is directly proptional to the cube of the length of its orbits semi major axis o Explains higher orbital velocities of inner planets Newton - showed Keplers laws can be derived from his 3 - found the formula to express the force of gravity - able to mathematically to describe the orbits of the planets and their satellites, the moon, comets, asteroids - laws were used by friend, Edmond Halley to predict the reappear of a comet - also used by Adams and Leverrier to find a planet beyond the orbit of Uranus, based on slight irregularities in that planets orbital motion: Neptune - Law #1- a body remains at rest or moves in a straight line at a constant speed unless acted upon by a net outside source (the law of inertia) o Planets would leave their orbits if no forced acted on them - Law #2- acceleration of an object is proportional to the force action up it o Force equals mass times acceleration - Law #3- whenever one body exerts a force on the 2nd body the 2nd exerts on equal and opposite force on the 1st o The law of “action and reaction” Retrograde motion – Planets seem to have stop and then back up for the reverse movement to the west relative to the background stars Tycho Brahe ~most accurate observational astronomer (pre-telescope) - observed a new star in Cassiobeia and comets with no parallax - believed the sun revolved around the earth - kept accurate records of the planetary obsercations over a period of about 20 years - hired Kepler as his assistant died because he drank to much and couldn’t go to the bathroom (socially wrong) Copernicus- model is complex and required the use of epicycles - planets closer to the sun move faster - worked out a relative seate(?) for the solar system - earth to the sun distance is one AU (astronomic units) Renaissance Astronomy – Copernicus, Tycho Brahe, Kepler, Galileo, Newton Aristotle – he observed earth centered shadow on the moon during a lunar eclipse - knew that ones view of the sky changed with travel north or south - concluded that earth was a sphere - understood the cause of lunar phases Aristarchus (heliocentric model) - measured the relative distances to the moon and sun - realized that the sun was much larger than the earth - put earth in orbit around the sun even though he had no proof (parallax) Eratosthenes- measured the earth’s circumference - At Alexandria measured the points by using the sun (7 degrees( Hipparchus - Made accurate observations/produced a catalog of 850 plus stars - Revived a magnitude scale to compare star brightnesses - Detected slight change in the norm celesnalpede - Determined the length of the year to within 6 minutes - Recognized the sun’s annual apparent motion was irregular; the sun appeared to move faster new the winter solstice and slower at summer solstice - Explained how planets could move from direct retrograde motion and still orbit earth Ptolemy - earth centered cosmology which remained in favor into the 1400’s - complied the almagest, a collection of material from earlier astronomers - explained retrograde with epicycles and circular planetary orbits - produced one of the earliest accurate maps of the Mediterranean region - though the earth’s circumference was only 19.000 miles Scientific notation- “powers of ten”(much larger or smaller then one)