Tuesday June 14th the outermost of the 8 planets, Neptune, pauses its regular eastward direct motion around the Sun and for the next several months will appear to be moving westward, in retrograde motion, across the constellation Aquarius the Water Bearer. Neptune’s retrograde motion ends on November 20th with Neptune resuming its eastward direct motion.
Retrograde motion is an apparent motion that the outer planets, relative to the Earth, have. It is an apparent motion that looks as if the outer planet stops it normal direct motion to the east and reverses direction to the west. After a period of time the apparent westward motion ends and the planet resumes its normal orbital path to the east. Retrograde motion happens as the faster moving Earth catches up with and then passes by the outer planet. It is during this time that the backward apparent motion happens.
The two inner planets also have retrograde motion but it is a result of their orbit around the Sun and not the Earth passing them by. For approximately one-half of their orbit they move east, from western elongation through superior conjunction to eastern elongation. Then at eastern elongation the inner planet starts moving westward through inferior conjunction to western elongation.
Read a little more about retrograde motion in my February 2012 Scope on the Skies column, drawkcab planets, in Science Scope Magazine.
Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.