Where the horse stands on the compass
Wu runs from 172.5 to 187.5 degrees. It is an earthly branch, the horse of the zodiac, the hour from 11 am to 1 pm, the summer solstice. Its element is fire, and it sits in the Li trigram between Bing at 165 and Ding at 195. Its opposite is Zi at 0 degrees, the seat of Tianlei. On the star ring, Tianma is the name in the slot directly above Wu. The neighbours are Taiwei over Bing and Tianzhu over Ding. Both of those mountains are six elegant; Wu is not, and its star carries no rank.
What the school reads from it
Our school uses the star ring to confirm what the hills already show, not to replace them. Lai Buyi's Cui Guan Pian goes through dragon, hollow, sand and water in turn and answers each with a star of the 24. Tianma is an ordinary star, so its job is modest. A clean peak standing on Wu, a road coming in on that bearing, water arriving from the south: the star reads these as movement and says the landform is what it looks like. It does not lift a site. If the hill in front is ragged, or the road on 180 degrees runs straight at the door, Tianma confirms a bad reading.
What this means on the ground
Find it from the site, not from a map. At a grave, stand behind the stone and sight along its face; at a house or shop, stand inside the main door with your back to it and look out. Level the luopan, let the needle settle, take three readings, and keep steel out of reach. If the facing peak reads between 172.5 and 187.5, it stands on Wu, and the slot above it on the star ring is Tianma. Then look at the thing itself. A rounded, whole hill at that bearing is the case hill you want, and in a city a well shaped building plays the same part. A T junction or a straight road aimed in on 180 degrees is the opposite, and the star changes nothing about that.
Common mistakes
A phone compass has no star ring, so there is nothing to read; it also defaults to true north, and overseas the magnetic variation can push a reading into Bing or Ding. Set it to magnetic north and use it only as a rough check. Do not treat the name as a verdict. Horse, movement, speed are the imagery behind the name, not a forecast for the family. Do not count stars before you have walked the dragon and looked at the water mouth. And do not take bearings off a satellite image; stone, door and peak have to be sighted from where you stand.
Questions people ask
What star is on Wu mountain in feng shui?
Tianma, Heaven's Horse. It occupies the star ring slot over Wu, 172.5 to 187.5 degrees, due south. It is an ordinary star, and it is read as confirmation of the landform on that bearing.
Is Tianma a good star?
It has no rank. The four noble stars are Tianhuang, Tianshi, Taiyi and Shaowei; Tianma is not one of them. A fine peak on Wu is fine because of the peak, and the star only agrees with it.
What does Heaven's Horse mean for a south facing house?
A house that sits north and faces south has Wu, and so Tianma, straight out the front door. Read what is there: a clean building or hill is good sand, an oncoming road is not. The star does not change the answer.
Book a site reading with Master Zhang, or join a field course in Ganzhou and learn to sight a peak with the luopan in your own hands.