Tian Yue (moon): a minor star looked up month by month

Two stars with one sound: the moon looks at the month, the axe at the stem

A chart page can show two stars that both read as Tian Yue: the minor star Tian Yue (天月) and the supporting star Tian Yue (天钺), written one character apart. The first has the character for the moon, here the lunar month; the second has the character for an ancient battle-axe and pairs with Tian Kui. This article is about the first.

Two charts that differ by one year show it best. Both birthdays are the tenth day of the sixth lunar month; one chart is a Yin Earth year and the other a Yang Metal year:

The site keeps minor stars and supporting stars in different data groups, so one sound cannot merge them, and its English interface labels them Tian Yue (Ailment) and Tian Yue (Night Patron). The label table's own note says the name of the moon-character star carries the sense of a "sickness charm" and does not refer to the moon. That is the traditional sense of the name, it says nothing about anyone's health, and its classical source is still to be checked. The axe-character star has its own article, Tian Yue: where the supporting star sits and what it does.

Twelve months, eight spots

The verse hands out a spot for each month. The verse below sits in a code comment of iztro, where animals stand in for branches. Our translation:

One is the Dog, two the Snake, three the Dragon; four the Tiger, five the Goat, six the Rabbit. Seven the Pig, eight the Goat, nine the Tiger; ten the Horse, winter the Dog, last month in Tiger.

Open the full-size diagram

Comparison sketch: spots are taken from the site engine for all twelve months and grouped by branch; rows in one color are spots that take more than one month.

Turning animals into branches is direct: the Dog, Snake, Dragon, Tiger, Goat, Rabbit, Pig and Horse are the branches of those names, and the last line names the Tiger branch outright. Not once in the three volumes of the Zi Wei Dou Shu Quan Shu (紫微斗数全书) does Tian Yue appear, so what follows covers only the engine's placement.

Three month-placed stars, three shapes

More minor stars than these follow the lunar month (Tian Yao, Tian Xing and Yin Sha do too); set three of them side by side, Tian Wu, Jie Shen and Tian Yue, and their tables have different shapes: some can be written as a formula and some can only be looked up.

From one month to the next, Tian Yue moves forward by 7, 11, 10, 5, 8, 8, 8, 7, 4, 4 and 4 branches in turn. No fixed step exists, so remainders or half-years will not reproduce it. The other two stars have articles of their own: Tian Wu cycles in groups of four and Jie Shen changes spot every second month.

One month boundary, two of three stars move

A month boundary shows the difference between the tables best. July 5, 2024 was the thirtieth of lunar month five, and the next day, July 6, was the first of month six:

Going from month five to month six moves Tian Yue and Tian Wu but leaves Jie Shen on the Rat, because its verse puts months five and six on one spot. Comparing two charts across a month boundary therefore means looking up each star, not just noting that the month changed. Leap months depend on the setting: the leap fourth month of 2020 shows it: day fifteen (June 6) counts as month four and puts Tian Yue on the Tiger, while day sixteen (June 7) counts as month five and moves it to the Goat. Why one setting can change a whole chart is covered in the leap-month and day-boundary article.

Tian Yao, Tian Xing and Yin Sha also read only the lunar month; their inputs, and those of the remaining minor stars, are listed in the input table of the minor-star overview.