Mercury will be retrograde in sidereal Sagittarius from December 26 until January 15, 2010.
When a planet goes retrograde it appears to move backwards relative to our position here on Earth. This backwards motion internalizes its energy, making it more of a psychological factor.
In Vedic astrology this phenomena is called "Chesta bala" which translates to "Motional strength . In Vedic astrology, a retrograde planet gains a certain type of strength, because when the planet is retrograde it is closer to the Earth. When we consider astrology is an observable science, the retrograde planet becomes "closer" to us when it moves backwards.
One way we feel this closeness, is when things related to that planet mess up in our life. These "mess ups" are generally what is discussed when a planet goes retrograde. The things it relates to in our external, worldly life may become frustrating. But this frustration is a catalyst for deeper introspection and greater skill with that thing in the future.
As it relates to Mercury, details and communication issues can be problematic when he goes retrograde. But these problems internalize our relationship with those details, what we say, et cetera - and thereby improve those things in the future.
Using the sidereal zodiac, the zodiac used in Vedic astrology (and by many western astrolgers as well), this retrograde cycle will take place in Sagittarius.
In general, when Mercury is in Sagittarius, there's a little bit of difficulty. This is because Mercury is a practical, rational and neutral influence in our life. You can think of Mercury as an accountant.
Sagittarius is a very hopeful and inspired sign.
What's wrong with that you may ask,... what's wrong with having an inspired or hopeful accountant?
Well, is it better to plan your monthly budget on how much money you actually have or how much money you hope to have? Mercury is a part of us that makes decisions based on the facts as they are - unbiased by hope, pessimism, etc.
Mercury has been in Sagittarius since December 1 and will remain there until February 5, 2010. This entire Mercury cycle is a time where we must be careful overplaying our hands, over expressing ourselves, exaggerating our words, et cetera.
Between December 26, 2009 and January 15, 2010 - these exaggerations in communication may come back to haunt us.
What can you do:
Try to stay practical and realistic in what you say and be careful about overplaying your hand, especially around things that have to do with money. (Christmas gifts anyone?) Mercury is literally related the cash you have - Jupiter is the line of credit you are running.
If you overplay your hand now - you may have no cards to play with between December 26, 2009 and January 15, 2010 - Mercury's retrograde period.