The constant star and its mountain
Wei is an earthly branch, the goat of the zodiac, the hour from 1 to 3 pm, element earth. It sits in the Kun trigram between Ding at 195, seat of Tianzhu, and Kun at 225, seat of Tianyue. Its opposite is Chou at 30 degrees, seat of Tianchu. On the star ring the name over Wei reads Tianheng. Constancy is a quiet image next to the horse on Wu or the axe on Kun, and that is the point: the school looks here for things that stay put. A long, low, even ridge on Wei fits the name. A sharp, restless outline does not, and the name does not make it fit.
What heaven confirms and what it does not
The rule of this school is heaven confirms earth: the star has nothing to say until the hills have spoken. Lai Buyi's Cui Guan Pian treats dragon, hollow, sand and water in four chapters and sets a star against each; we follow that order. When the dragon enters the head from Wei, when a guarding hill stands on Wei, or when water comes in from 210 degrees, the star ring reads Tianheng and takes it as a sign that the form is steady and lasting. That is all a plain star can do. If the hill on Wei is broken by a quarry, or the water from 210 comes straight and fast, the star confirms a weak site. It never argues the other way.
What this means on the ground
Grave: stand behind the headstone and read along its face, then swing the plate to the hill or the water. House or shop: stand inside the main door, back to it, facing out. Level the luopan, wait for the needle, read three times, no steel nearby. A bearing between 202.5 and 217.5 is Wei; the star ring slot above it says Tianheng. Near 203 you are almost on Ding, near 217 almost on Kun, and the line itself is to be avoided for a stone or a door. For a shop, a long settled row of buildings at this bearing is what the name describes; a junction feeding traffic in from 210 is the opposite, whatever the star is called.
Common mistakes
Reading the name as a forecast. Constant does not mean a family's fortune is fixed; it is the image carried by the bearing. Mixing up the two Tianheng stars. The Constant is over Wei at 210; the Beam is over Geng at 255. Checking the star ring on a phone, which has none and is usually set to true north, so that a Wei reading drifts onto Ding or Kun. Counting stars before walking the dragon and finding the water mouth. Taking bearings from a satellite image instead of from the stone.
Questions people ask
Which star is on Wei mountain in feng shui?
Tianheng, Heaven's Constant, over 202.5 to 217.5 degrees, south south west. An ordinary star: it confirms what a hill or water on that bearing shows and has no rank of its own.
Are there two stars called Tianheng?
In pinyin, yes. Heaven's Constant is written with the character for constancy and sits on Wei at 210. Heaven's Beam is a different character and sits on Geng at 255. Check the character, not the sound.
Does Tai Sui on Wei in 2027 change the reading?
The star does not change. In the Ding Wei year of 2027 Tai Sui sits on Wei, and the custom is to avoid breaking ground or setting a stone on that side that year. That is a timing rule, separate from the star ring.
Ask Master Zhang to read the hills behind your plot, or learn to do it yourself on a field course in Ganzhou.