TL;DR: For people born in a leap month or the Tý hour, the books differ on which month and which day to use when casting a Purple Star chart. Tử Vi tổng hợp (Nguyễn Phát Lộc) casts by the exact month number and considers advancing by one month to be wrong; Tử Vi đẩu số tinh thành takes the following month; Từ Tăng Sinh records a split at the 15th day. For the Tý hour, Tử Vi đẩu số tinh thành changes the day at midnight, while Tử Vi tổng hợp writes the day as beginning from the Tý hour. The Purple Star tool of Nhật Nguyệt keeps the original leap month number and uses exactly the solar date that was entered.
Why are leap months and the hour of Tý the hard spots in a Tử Vi chart?
This article compares two Vietnamese Tử Vi books, Tử Vi đẩu số tân biên by Vân Đằng Thái Thứ Lang and Tử Vi tổng hợp by Nguyễn Phát Lộc, with two books translated from Chinese, Tử Vi đẩu số tinh thành and Tử vi đẩu số Mệnh vận phân tích by Từ Tăng Sinh. Tử Vi Đẩu Số places stars by the lunar calendar. Từ Tăng Sinh writes that Tứ Trụ and Western astrology both use the solar calendar, and that Tử Vi Đẩu Số alone uses the lunar calendar[4]. Because it holds to the Moon's calendar, the discipline has to deal with two spots: leap months, and the day of a person born in the hour of Tý.
Leap months exist to make up the gap between the lunar year and the solar year: every 19 years a lunisolar calendar inserts 7 leap months, a figure that the translator's note in Từ Tăng Sinh's book also mentions[4]. A leap month repeats the number of the month before it, so when stars are placed by birth month the chart-maker has to decide which month it counts as. Every dispute starts here.
The hour of Tý is the same. The hour of Tý runs from 23:00 the previous day to 1:00 the next day, that is, it straddles the day boundary. Vân Đằng Thái Thứ Lang's book Tử Vi đẩu số tân biên defines the hour of Tý as the period from 23:00 to 1:00. But a birth date has only one day, so the question arises: a person born at 23:30 on the 5th is counted as the 5th or the 6th? The two answers give two different birth dates, and with them the whole day pillar and all stars placed by day change.
What do the books say about leap months?
Tử Vi đẩu số tân biên and counting months to place palaces
Vân Đằng Thái Thứ Lang's Tử Vi đẩu số tân biên sets out the procedure for placing the Mệnh and Thân palaces by counting the birth month[1]. The method: take the Dần palace as the first month, count forward by birth month, and whichever palace you stop at is called the "hour of Tý"; from that palace, count backward to the birth hour to place Mệnh, and count forward to the birth hour to place Thân. The book also notes that the Thân palace can only fall in six fixed palaces, namely Mệnh Viên, Phúc Đức, Quan Lộc, Thiên Di, Tài Bạch, Thê Thiếp or Phu Quân; if Thân lands in another palace it is wrong and must be checked again.
For leap months, this book devotes no separate section, but its whole method of counting months assumes each year has exactly twelve months corresponding to the twelve branches from Dần to Sửu. That means a leap month must be reduced to one of those twelve positions.
The two methods in Tử Vi đẩu số tinh thành
Tử Vi đẩu số tinh thành (紫微斗数精成), a Chinese book with a Vietnamese translation, gives two ways of handling a leap month. The first is used when casting the chart: for a person born in a leap month, take the following month. A birth in a leap first month is reckoned by the second month, a birth in a leap fifth month by the sixth month[3]. The consequence is that one month is doubled: a person born in a leap first month and a person born in the second month both have their stars placed by the second month[3].
The second way is reserved by the book for calculating Đẩu Quân lưu nguyệt: split the leap month in two, from the 1st to the hour of Hợi on the 15th belonging to the previous month, and from the 16th to the end of the month belonging to the following month[3]. The book notes that some schools also use this way to cast the chart. On the author's own choice the two versions do not match: the Vietnamese translation has the author finding the first way more reasonable, while the Chinese sentence printed alongside says that when the first way does not fit the facts one may try the second[3].
Tử Vi tổng hợp and a different view
Tử Vi tổng hợp by Nguyễn Phát Lộc says the opposite. Listing the factors of a chart, the book writes: "Những tháng nhuận ta không kể vì lá số Tử-Vi cứ an theo tháng, bất luận tháng thường hay tháng nhuận" (leap months are not counted separately, because a Tử Vi chart is placed by the month, whether ordinary or leap)[2]. In its section on mistakes in drawing up a chart, the book even names the practice of moving to the next month: "Có người sinh vào tháng nhuận, rồi cứ đôn lên 1 tháng, làm sai lạc tháng sinh" (some people born in a leap month push it up by one month and so get the birth month wrong)[2].
There are thus three ways: keep the month number (Tử Vi tổng hợp), move to the following month (the first way in Tử Vi đẩu số tinh thành), and split at the 15th (the second way in that book, and also the way Từ Tăng Sinh calls common). All three are conventions of the books, not results of calendar computation. Nhật Nguyệt's Tử Vi chart tool follows the first way: a birth in a leap fourth month is placed by the fourth month.
Born in a leap month, which month should the chart use?
There is no common answer; depending on the book, a person born in a leap month is placed by that same month number, by the following month, or by the previous or the following month according to whether the birth falls before or after the 15th.
Take a person born on the 10th of a leap fourth month. Counting from Dần as the first month, the fourth month corresponds to the Tỵ palace and the fifth to the Ngọ palace. By Tử Vi tổng hợp, this person is placed by the fourth month, with the Tỵ palace as the starting point for the hour of Tý[2]. By the first way in Tử Vi đẩu số tinh thành, this person is placed by the fifth month, starting from the Ngọ palace[3]. By the split method, the birth falls before the 15th and so is still placed by the fourth month. From that starting palace one counts backward to the birth hour to place Mệnh and forward to place Thân, so the two ways give Mệnh palaces exactly one palace apart.
Tử Vi đẩu số tân biên prescribes that Tả Phụ starts from the Thìn palace as the first month and counts forward to the birth month, while Hữu Bật starts from the Tuất palace as the first month and counts backward to the birth month[1]. So once the leap month is changed to an ordinary month, all month-based stars shift in a consistent way.
A difference of one month changes the Mệnh palace, the Thân palace, the cục and every star placed by month, so two people with the same leap-month birth date, charted by two books, end up with two different charts.
Born in the hour of Tý, which day counts?
For the hour of Tý, Tử Vi đẩu số tinh thành gives a concrete marker: within one day, the periods from 0:01 to 1:00 and from 23:01 to 24:00 both belong to the hour of Tý of that day[3]. A person born before midnight still counts as the late hour of Tý of the old day, and only after midnight as the early hour of Tý of the new day[3].
In other words, by this book the day changes at midnight, not at 23:00. A person born at 23:30 on the 5th still belongs to the 5th although already in the hour of Tý; a person born at 0:30 belongs to the 6th. The hour of Tý is thereby split into two halves belonging to two days. Nhật Nguyệt's Tử Vi chart tool does the same: the chart takes the lunar date of exactly the solar date entered, even for a birth between 23:00 and midnight.
Tử Vi tổng hợp by Nguyễn Phát Lộc points in another direction. In its section on mistakes in drawing up a chart, the book writes: "Ví dụ như sinh vào 1 giờ rưỡi đêm 18 rạng 19 thì phải lấy ngày 19 làm ngày sinh, vì ngày 19 bắt đầu từ giờ Tý" (a birth at 1:30 in the night of the 18th going into the 19th must take the 19th as the birth day, because the 19th begins from the hour of Tý)[2]. The book's example is the hour of Sửu, after midnight, so it does not touch the period from 23:00 to midnight; but if the day begins from the hour of Tý, that is from 23:00, then a person born at 23:30 already belongs to the next day. The book does not state this case outright.
| Birth situation | Tử Vi đẩu số tinh thành | Tử Vi tổng hợp |
|---|---|---|
| 23:01 to 24:00 on the 5th | Belongs to the 5th, late hour of Tý[3] | Not stated separately; by the sentence "the day begins from the hour of Tý" it is already the 6th[2] |
| 0:01 to 1:00 on the 6th | Belongs to the 6th, early hour of Tý[3] | Belongs to the 6th |
| 1:30 in the night of the 18th going into the 19th | Belongs to the 19th | Belongs to the 19th[2] |
Only the period from 23:00 to midnight is where the two ways give two different days. Nhật Nguyệt's Four Pillars tool turns the day at 23:00, as in most Tử Bình texts, so for a birth in this period the Tử Vi chart and the Four Pillars chart on Nhật Nguyệt can give different days; to have the Tử Vi chart follow the rule of turning the day at the start of the hour of Tý, enter the next day's date.
Why do the books disagree?
The deep reason is that Tử Vi Đẩu Số has no single standard text on calendar rules. Từ Tăng Sinh's Tử vi đẩu số Mệnh vận phân tích remarks bluntly: the leap-month problem causes tremendous confusion, and in the end whether a person born in a leap month counts as the previous or the following month is something each person says differently, with no one yet giving reasons that fully convince others. This book records the common practice in Tử Vi Đẩu Số as taking the 15th of the leap month as the dividing point, before the 15th counted by the previous month and after the 15th by the following month. So within one book we already see a rule different from Đẩu số tinh thành's "take the following month".
It should also be noted that the rule using the 15th as the dividing marker for a leap month, which Từ Tăng Sinh mentions, resembles the second method in Đẩu số tinh thành, which that book reserves for calculating Đẩu Quân lưu nguyệt rather than for setting up the birth chart[3]. A rule used for one purpose in one book and another purpose in another shows how discretionary the matter is.
The consequence is that when casting a chart for a person born in a leap month, the caster must state which convention is being followed. For the same person, counting the leap month as the following month can shift the Mệnh palace by one palace compared with counting by the original month, and with it all twelve palaces and a whole series of month-based stars shift. This is not a small margin of error but a structural difference in the chart.
Other errors to check before placing stars
Nguyễn Phát Lộc's Tử Vi tổng hợp lists a series of causes that skew a chart, notably the birth hour problem. The book states that Vietnamese time has changed many times since 1943, rising and falling as many as six times, at one point by up to two hours, so the caster must compensate. This is very practical: a person who reports the hour of Tý by wristwatch may actually have been born in the hour of Hợi or Sửu by solar time, if the time-zone change is not accounted for.
The book also lists other cases such as being born exactly on the boundary of two successive lunar hours, for example 1 p.m. as the boundary between the hour of Ngọ and the hour of Mùi; late registration followed by gradual forgetting of the real birth date and use of the registered date instead; and misplacement of stars. For people born in a leap month, the book notes that some simply push the month up by one, distorting the birth month.
For a person born in the hour of Tý the check matters all the more because the hour sits on the day boundary: one must know whether the birth was before or after midnight, and which day-change rule the chart is following.
In short, what do the books say?
There is no single answer to either question. For leap months, Tử Vi tổng hợp keeps the month number and counts pushing it up a month as a mistake[2]; Tử Vi đẩu số tinh thành takes the following month[3]; Từ Tăng Sinh records splitting at the 15th as the common practice and admits that no one has yet given a fully convincing reason[4]. For the hour of Tý, Tử Vi đẩu số tinh thành changes the day at midnight[3], while Tử Vi tổng hợp writes that the day begins from the hour of Tý[2].
Nhật Nguyệt's suggestion: when casting a chart for a person born in a leap month or between 23:00 and midnight, note which way the chart follows, and when comparing two charts of the same person cast both the same way. Nhật Nguyệt's tool keeps the leap month's number and uses exactly the date entered; to see the chart by another way, enter a solar date that corresponds to the lunar month or lunar day of that way.
