Transcript Retrograde Motion
Retrograde Motion You’re going the wrong way! 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 superior 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 The Ecliptic Line The Ecliptic Apparent path of the Sun and planets through the night sky The Ecliptic Q: How far (in degrees) would the Sun move along the Ecliptic each day over the course of 1 year? Hint: There are 360º in a circle and 365 days in a year A: about 1 degree (width of your baby finger at arm’s length) The Zodiac 16 degree wide band centered on the Ecliptic is called the zodiac Broken into 12 constellations (groups of stars) or signs each covering 30 degrees of sky What’s your ‘sign’? What’s your sign? Sign Symbol Dates Aries Ram March 21 - April 19 Taurus Bull April 20 - May 20 Gemini Twins May 21 - June 20 Cancer Crab June 21 - July 22 Leo Lion July 23 - August 22 Virgo Virgin August 23 - September 22 Libra Balance September 23 - October 22 Scorpio Scorpion October 23 - November 21 Sagittarius Archer November 22 - December 21 Capricorn Goat December 22 - January 19 Aquarius Water Bearer January 20 - February 18 Pisces Fish February 19 - March 20 Star Charts Let’s check out the star charts!