Neptune Backs Up

Two days in a row! Like the song goes, “slow down you move too fast” – or proofread!!
   Friday June 16th the outermost of the 8 planets, Neptune, ends its westward retrograde motion around the Sun and will resume direct motion, moving eastward will come to an apparent halt in its eastward or direct motion and appear to start moving backward to the west in what is known as retrograde motion. In this graphic the location of the 21.5-day old waning gibbous Moon is shown to be about 2-3o from Neptune. Neptune has an apparent magnitude of nearly 8.0 making it all but only visible with telescopes – and certainly not on this date with -12th magnitude Moon nearby.

   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 monthly observing information, or here to return to bobs-spaces.

1 thought on “Neptune Backs Up

  1. Hey, Bob, need some ed. help for my daughter who teaches m.s. science in STL. She’s in charge of activities for the whole school (300 kids), for eclipse day, Aug. 21. Could you e-mail me at so I can chat at you about ideas? Thanks, Therese Keirsey


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.