retrograde motion you’re going the wrong way!. history of retrograde motion ancient greeks noticed...
TRANSCRIPT
History of Retrograde MotionHistory of Retrograde Motion
Ancient Greeks noticed that certain Ancient Greeks noticed that certain celestial objects changed their celestial objects changed their locations from time to timelocations from time to time
They called them “wanderers”; They called them “wanderers”; ‘planet’ comes from that Greek word ‘planet’ comes from that Greek word
Greeks charted stars and planets, Greeks charted stars and planets, noticed that planets seemed to stop noticed that planets seemed to stop and change direction sometimesand change direction sometimes
Retrograde MotionRetrograde Motion
On Earth, planets appear to move from On Earth, planets appear to move from east to west due to our rotation (prograde east to west due to our rotation (prograde motion)motion)
Once in a while, planets appear to stop and Once in a while, planets appear to stop and move west to east (retrograde motion)move west to east (retrograde motion)
Retrograde MotionRetrograde Motion
For superior planets (further from the For superior planets (further from the Sun than Earth)Sun than Earth)
Earth orbit is faster than these Earth orbit is faster than these planetsplanets
Earth catches up to a planet in its Earth catches up to a planet in its orbitorbit
Planet appears to stop and move Planet appears to stop and move backwards (West to East)backwards (West to East)
YouTube “Retrograde Motion and the YouTube “Retrograde Motion and the Opposition of Mars”Opposition of Mars”http://http://www.youtube.com/watch?vwww.youtube.com/watch?v=72FrZz_zJFU=72FrZz_zJFU
The EclipticThe Ecliptic
Apparent path of the Sun and planets Apparent path of the Sun and planets through the night skythrough the night sky
The EclipticThe Ecliptic
Q: How far (in degrees) would the Q: How far (in degrees) would the Sun move along the Ecliptic each day Sun move along the Ecliptic each day over the course of 1 year?over the course of 1 year?
Hint: There are 360Hint: There are 360º in a circle and º in a circle and 365 days in a year365 days in a year
A: about 1 degree (width of your A: about 1 degree (width of your baby finger at arm’s length)baby finger at arm’s length)
The ZodiacThe Zodiac
16 degree wide band centered on the 16 degree wide band centered on the Ecliptic is called the Ecliptic is called the zodiaczodiac
Broken into 12 constellations (groups Broken into 12 constellations (groups of stars) or of stars) or signssigns each covering 30 each covering 30 degrees of skydegrees 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
What’s your sign?What’s your sign?