There are five planetary ingresses this month. Venus and Mercury move into Scorpio within hours of each other as December begins, Mercury moves into Sagittarius on Dec 12th, The Sun enters Capricorn at the Solstice on December 21st, and Mars enters Aries on the last day of the year, auguring a bombastic New Year’s Eve.
Melting down the zodiac
The passage of Mars through Pisces during the month of December makes for a fitting finale to the calendar year. This is the last sign of the twelve; in a way, it is an amalgam of all the signs that preceded it. Pisces’ job is to melt the zodiac down into a stew, as the cycle gets ready to start again.
This blending together of disparate energies is what Mars in Pisces so elusive.
Take note of what houses are traversed in your chart, and what (if any) aspects formed, by 9°–29° degrees of Pisces. The transit may manifest as a kind of restless irritability, or a sense of floating dreamily through the month.
Softened impulses
It may seem harder to know what we want, because this Mars placement downplays the individuality. This is especially pronounced given that Neptune too is in Pisces, softening our independent impulses.
Pisces seeks a collective sensibility, or even a cosmic 
context, in which to disappear. Positively, this encourages altruistic, spiritual and imaginative activity. Negatively, it promotes passivity; a surrender into the mob mind.
Expect either tendency to peak around the 2nd (Mars square the Sun), the 5th (Sun square Neptune), the 6th and 7th (Mars conjunct Neptune) and the 24th (Mercury square Neptune) of December.
Winter Solstice
The sacred Solstice is a highly charged event. Although the secular world has lost touch with its layered meanings, this annual threshold retains a primordial power that reverberates though our psyches (see this article).
This year, the Sun’s passage from mutable Fire into cardinal Earth takes place on Friday Dec 21st (2:24 pm PST) — just hours before the Full Moon, making it more resonant still.
The mysterious beginning of winter in the Northern Hemisphere is announced by an intangible spark in the darkness. The great irony of the Solstice, and the clue to its esoteric meaning, is the fact that here in 
the deep bowels of winter, with the nights maximally long and the days maximally short, along comes this official announcement of the return of warmth and light.
Starting gun
Sensitive souls may feel another palpable shift at the Mars ingress, just as the old year is morphing into the new (12/31 6:21 pm PST). The mood in the air of vague dreaminess (Pisces) will transform into a fiery surge of forward motion (Aries), like the pop from a starting gun.
Images
The Night Before Christmas by Arthur Rackham
Blackbirds by Ogata Korin
Photo of submerged figure by Gabrielle Wittkop
