The ongoing Mutable T-Square is the whole of September's planetary transit patterns. Like in past months, there is a fleeting Mutable Grand Cross when the Moon makes its monthly pass through Gemini.
A T-Square is basically a 90-degree triangle, with at minimum 3 planets involved in a square (2 at 180 degrees from one another). This month it is between the North Node, Mercury, and the Sun in Virgo, with Mars and Saturn in Sagittarius, and Neptune and Chiron in Pisces.
Sep 01, 2016
T-Square: North Node in Virgo 12° , Mars in Sagittarius 14° , Sun in Virgo 9° , Saturn in Sagittarius 10° , Neptune in Pisces 10° Moon in Virgo 12°
The month starts off with a super T-Square, as the Moon passes through Virgo and joins the T-Square.
Sep 12, 2016
T-Square: Mercury in Virgo 21° , Chiron in Pisces 23° , Mars in Sagittarius 20° , Sun in Virgo 19°
T-Square: Neptune in Pisces 10° , Saturn in Sagittarius 10° , North Node in Virgo 12°
The T-Square remains strong throughout the month, but around the 12th the Sun begins to move through the later degrees of Virgo as Mercury is retrograding back into Virgo. This causes the T-Square to break off into two Mutable squares.
The Sun, Mercury, and Mars - all fast-moving planets - square with Chiron in Pisces.
Sep 19, 2016
T-Square: Sun in Virgo 26° , Mars in Sagittarius 24° , Chiron in Pisces 22°
T-Square: Mercury in Virgo 15° , North Node in Virgo 11° , Saturn in Sagittarius 10° , Neptune in Pisces 10°
By the 19th, Mercury has retrograded (basically moved backwards) far enough through the sign of Virgo that it joins the T-Square that lies in the earlier degrees - along with the North Node, Saturn and Neptune.
Meanwhile, this is the last day of the first T-Square, as the Sun has progressed far enough through Virgo that it ceases to make a 90 degree angle to Chiron. In astrology, an 8 degree orb (or margin of error) is required to consider the aspect a square. However, the Sun and Mars still remain in a tight square to one another.
Sep 22, 2016
T-Square: Mercury in Virgo 14° , North Node in Virgo 11° , Saturn in Sagittarius 11° , Neptune in Pisces 10°
Grand Cross: Mercury in Virgo 14° , Neptune in Pisces 10° , Moon in Gemini 14° , North Node in Virgo 11° , Saturn in Sagittarius 11°
As was the case in previous months, the Moon completes the Mutable T-Square and creates a Mutable Grand Cross as it passes through the sign of Gemini.
Mercury officially drops from the T-Square around Sept 28th leaving the remaining three planets in the planetary pattern for the remainder of the month.