T H Murrey provides our first hint in a note he wrote on August 19, 1997. I will quote the first sentence of that message.
My starting day each fall was originally started on the 14th day after the fall equinox . . .
The Fall Equinox occurred at 11:57 pm GMT on September 22, 1997. Fourteen days after the Fall Equinox would occur on late on October 6, 1997. However, T H Murrey started the Fourth Quarter of 1997 on Friday, October 3rd. He did not follow his own rule.
|1993||Wed, Jan 6|
|1994||Wed, Jan 5|
|1995||Tues, Jan 10|
|1996||Tues, Jan 9|
|1997||Tues, Jan 7|
|1998||Tues, Jan 6|
What occurs "early" in January? The Earth reaches perihelion on January 4th of each year. The following table lists the start of the First Quarter, the date and time of the Perihelion, and the Delta between the two dates.
The Delta is positive if the start of the First Quarter occurs after the Perihelion. The Delta is quoted in trading days.
|1993||Wed, Jan 6||+ 2 days||Mon, Jan 4||3:05 am GMT|
|1994||Thu, Jan 5||+3 days||Sun, Jan 2||5:55 am GMT|
|1995||Tues, Jan 10||+3 days||Wed, Jan 5||11:06 am GMT|
|1996||Tues, Jan 9||+3 days||Thu, Jan 4||2:27 am GMT|
|1997||Tues, Jan 7||+4 days||Wed, Jan 1||11:18 pm GMT|
|1998||Tues, Jan 6||+2 days||Sun, Jan 4||9:16 pm GMT|
T H Murrey appears to be starting the First Quarter "close" to the Earth's Perihelion in early January. The Winter Solstice occurs on December 21st, and the Earth's Perihelion occurs 14 days after the Winter Solstice. The Winter Solstice occurs when the Sun enters Capricorn. This astrological event is 90 degrees from the Fall Equinox (when the Sun enters Libra).
The Delta is positive if the start of the Third Quarter occurs after the Perihelion. The Delta is quoted in trading days.
|1993||Fri, July 9||+5 days||Sun, July 4||10:20 pm GMT|
|1994||Fri, July 8||+3 days||Tue, July 5||7:18 pm GMT|
|1995||Fri,July 7||+3 days||Tue, July 4||2:17 am GMT|
|1996||Thu, July 11||+4 days||Fri, July 5||7:01 pm GMT|
|1997||Thu, July 10||+4 days||Fri, July 4||7:21 pm GMT|
|1998||Thu, July 9||+4 days||Fri, July 3||11:51 pm GMT|
The Spring Equinox occurs on March 20th, and April 3rd would be 14 days after the Spring Equinox.
The Delta is positive if the start of the Second Quarter occurs after April 3rd. The Delta is quoted in trading days.
|1993||Wed, Apr 7||+2 days||Sat, April 3|
|1994||Thu, Apr 7||+4 days||Sun, April 3|
|1995||Tue, Apr 11||+6 days||Mon, April 3|
|1996||Wed, Apr 10||+5 days||Wed, April 3|
|1997||Wed, Apr 9||+2 days||Thu, April 3|
|1998||Tue, Apr 7||+2 days||Fri, April 3|
The Fall Equinox occurs on September 22nd, and October 6th would be 14 days after the Fall Equinox.
The Delta is positive if the start of the Fourth Quarter occurs after October 6th. The Delta is quoted in trading days.
|1993||Mon, Oct 4||-2 days||Wed, Oct 6|
|1994||Fri, Oct 7||+1 day||Thu, Oct 6|
|1995||Fri, Oct 6||+0 days||Fri, Oct 6|
|1996||Fri, Oct 4||-1 day||Sun, Oct 6|
|1997||Fri, Oct 3||-1 day||Mon, Oct 6|
|1998||Fri, Oct 2||-2 days||Tue, Oct 6|
|1999||Fri, Oct 8||+2 days||Wed, Oct 6|
|2000||Mon, Oct 9||+1 day||Fri, Oct 6|
|2001||Fri, Oct 5||-0 days||Sat, Oct 6|
|2002||Fri, Oct 4||-0 days||Sun, Oct 6|
|2003||Mon, Oct 6||0 days||Mon, Oct 6|
|2004||Fri, Oct 8||+2 days||Wed, Oct 6|
|2005||Mon, Oct 10||+2 days||Thu, Oct 6|
|2006||Mon, Oct 9||+1 days||Fri, Oct 6|
|2007||Tue, Oct 9||+2 days||Sat, Oct 6|
|2008||??||?? days||Mon, Oct 6|
The next table contains the theoretical and actual number of trading days in the year. The Cumulative Error assumes that the start of the Fourth Quarter was moved back by exactly four trading days. I did not consider any error caused by 2001.
T H Murrey did not shorten the Third Quarter in 1994.
As you can see, the starting dates for the four Quarters are slowly moving forward in time. The start of the First Quarter in 2006 should have been January 5th. However, it was shifted forward four trading days to January 11th.