* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download motionofobjects
Survey
Document related concepts
Earth's rotation wikipedia , lookup
Formation and evolution of the Solar System wikipedia , lookup
Planets in astrology wikipedia , lookup
Definition of planet wikipedia , lookup
History of Solar System formation and evolution hypotheses wikipedia , lookup
Late Heavy Bombardment wikipedia , lookup
Transcript
Motions of the Night Sky Stars, Sun, Moon, Planets Motions of the Stars • Objects rise in the east move across the sky, and set in the west. • Motion is known as daily or diurnal motion. Motions of the Stars (2) • Stars appear to rotate around the North Celestial Pole, earth’s axis of rotation projected out into space. • The points of sunrise and sunset change with the seasons • During the summer, the sun rises far to the north of east, sets far to the north of west, and spends up to 15 hours above the horizon. Compare these 3 sunrise points for the summer solstice, fall equinox, and winter solstice. Photos by Rick Pirko http://analyzer.depaul.edu/paperplate/Sunrise%20Sunset.htm This change in the sun’s apparent behavior is due to the 23.5o tilt of the earth’s axis, and is also the cause of our seasonal weather changes. The hyperlinks below illustrates further. http://www.scienceu.com/observatory/articles/seasons/seasons.html http://www.suntrek.org/earth-beyond/spinning-orbiting-earth/what-causes-seasons/watch-tilt.shtml Motions of the Moon • You can make 4 observations if you watch the moon move through the sky over several months: • First, the apparent size of the full moon varies from month to month. Motions of the Moon • From the different sizes of the full moon, we can conclude that the moon’s orbit is quite elliptical. • In fact it varies by 13.3% of the average distance. • Perigee or closest approach is 356,000 km. Apogee or farthest approach is 407,000 km, with an average of 384,000 km. Motions of the Moon 2nd Observation • The moon doesn’t orbit the earth on the ecliptic, but rather spends half its time above and half its time below the ecliptic. • The moon’s orbit is tilted or inclined http://www.mmscrusaders.com/newscirocks/eclipse/eclipses.htm Motions of the Moon 3rd Observation • The moon moves eastward against the background of stars and the moon lags behind the stars, rising 53 minutes later every evening. • The orbital motion results in the changing lunar phases. http://www.sumanasinc.com/webchttp://www.sumanasinc.com/webcontent/animations/content/moonphase.htmlontent/anisamples/astronomy/moonphase.html The hyperlink above illustrates the changing lunar phases as the moon orbits the earth. Motions of the Moon The 4th observation • The same side of the moon always faces the earth. This means that the moon rotates on its axis at exactly the same rate at which it orbits the earth. We call this “locked” rotation synchronous rotation. http://www.sckans.edu/~gangwere/LAS170a2/_27.html Synchronous Rotation of the Moon Retrograde Motion You’re going the wrong way! Motions of the Planets • The planets rise on the eastern horizon and set in the west, due to the earth’s rotation. However, like the moon, the planets usually move eastward against the background of stars. • How fast they move depends on their distance from the earth and their orbital distance from the sun. Motions of the Planets • Once or more each year the planets do something strange. They pause in their normal eastward (or prograde) motion, and begin moving westward (or retrograde) for a few weeks, pause again, then resume their normal eastward prograde motion. History of Retrograde Motion • Ancient Greeks noticed that certain celestial objects changed their locations from time to time • They called them “wanderers”; ‘planet’ comes from that Greek word • Greeks charted stars and planets, noticed that planets seemed to stop and change direction sometimes Retrograde Motion • On Earth, planets appear to move from east to west due to our rotation (prograde motion) • Once in a while, planets appear to stop and move west to east (retrograde motion) Time lapse of Mars Retrograde Motion • For planets further from the Sun than Earth – Earth orbit is faster than these planets – Earth catches up to a planet in its orbit – Planet appears to stop and move backwards (West to East) • YouTube “Retrograde Motion and the Opposition of Mars” http://www.youtube.com/watch?v=72FrZz_zJFU Motions of the Planets • More than any other motion of objects in space, this retrograde motion of the planets confused the ancient peoples and seriously affected the development of astronomy as a science.