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Retrograde Shadow Periods

If you have even a passing interest in astrology you have no doubt heard of retrograde planets and Mercury retrograde in particular. When, from our perspective on earth, a planet looks to be going backward, it is said to be retrograde. All the planets (but not the Sun or Moon) are capable of retrograde motion for various amounts of time.

An infographic with details of when the various planets of our solar system appear to be retrograde
Infographic with the frequency and duration of retrograde periods for the various planets.

When Mercury, which rules communications and transport among other things, is retrograde, we are told to act on the words with re as a prefix. Such words as redo, reapply, review, retrace, repair, recheck all apply. This is a time when going back over (just as the planet is going back over where it has just been) is advised, rather than moving forward.

With Mercury, the retrograde period lasts about 3 weeks. After those three weeks, you may think that it is now fine to move ahead with plans you may have put off because of the retrograde period.  However, it may not be smooth sailing just yet, as the retrograde planets have what are called shadow periods.

I have been caught in retrograde shadow periods, as I am sure many others have. You get through the retrograde period with no real mess-ups and breathe a sigh of relief. And then, it happens!

Something that you were worried might happen during the retrograde period happens. It might be an electronic device you purchased that just doesn’t work and you have to return to the store for a refund. Or your car breaks down. You shake your head and wonder why it is happening now; after all the retrograde period has just passed. You’ve likely just been caught in its shadow.

While a planet will only be retrograde for a certain amount of time, it is the degrees of the zodiac that it is travelling along during that retrograde that are relevant here.  When a planet first passes the point in the zodiac that it will retrograde back to, this is the start of the retrograde shadow period. 

When the retrograde period is over, the planet will take a while to catch up to where it was when it started the retrograde period.  It is not until the planet has caught up to where it started its retrograde motion that the retrograde shadow period ends. 

Here is a little visual example I did of retrograde motion on video. When the car (planet) is blue it is in direct motion and out of the retrograde shadow. When it is grey it is in direct motion but in retrograde shadow. When it is red it is in retrograde motion.

Here is another example, on December 4, 2017, Mercury stationed retrograde at 29 degrees Sagittarius. It then retrograded until the 22nd of December when it stationed direct at 13 degrees of Sagittarius.

Mercury last crossed over 13 degrees of Sagittarius on November 14, 2017. So, we can say that the shadow period started on the 14th of November 2017.

Illustration of a retrograde shadow period
Mercury stationed retrograde at 29 degrees and retrograded back to 13 degrees. As Mercury will be retracing its steps back to 13 degrees, the shadow period is considered to have started when Mercury first passed that degree in direct motion. Likewise, the shadow period is said to end when Mercury catches up to where it was when it first stationed retrograde (29° in this example).

When we look to see when Mercury will actually catch up to the degree it was at when it started its retrograde motion (29 degrees Sagittarius) we see that it will not cross that degree again until the 10th of January 2018.

Therefore the shadow period extends the dates that we need to be wary of Mercury being retrograde from November 14th, 2017 to January 10th, 2018. (All dates CST).


Born and bred in Brisbane, Australia, I have had a fascination with astrology since I was a child. I hold the STA’s Practitioners Level Certification in Horary and am currently studying Hellenistic Astrology.