Qi Men Dun Jia in the Southern Hemisphere: Solar Terms and Directions for Australia & NZ

Q: Should Yin Dun and Yang Dun be swapped south of the equator?

The mainstream tradition does not swap them and uses one set of solar terms worldwide. The reformist view that swaps them lacks classical grounding and large-scale testing. Qimena follows the mainstream practice.

Q: Are directions reversed in the Southern Hemisphere?

No. A favorable direction means an absolute compass direction. The noon sun is in the north down under, though, so judging direction by the sun is easy to get wrong. Use a compass.

Q: What longitude do I enter for Sydney?

Sydney is at 151.21° E, so enter the positive value 151.21. Southern latitude does not affect the time calculation.

Three Questions from Down Under

July in Melbourne is mid-winter, yet the Chinese calendar calls it “Minor Heat / Major Heat.” So southern-hemisphere practitioners ask three things: should the solar terms be reversed? Should the Yin/Yang cycles be swapped? Do the direction readings still hold?

Question 1: Reverse the Solar Terms? — Mainstream Answer: No

The “solar terms” used by Qi Men and BaZi are markers of the sun’s position on the ecliptic (Winter Solstice = the sun reaching 270° celestial longitude). They are astronomical events that occur at the same instant worldwide — there is no northern or southern version.

The mainstream traditional school (and virtually every charting tool): one global set of solar terms and Yin/Yang cycle rules. The Stem-Branch calendar records celestial mechanics, not local perceived temperature.
A minority reformist school: argues the seasons are flipped and the Yin/Yang cycles should be swapped south of the equator. An interesting position, but without classical textual basis or large-scale verification.

Qimena follows the mainstream: one global calendar. If your lineage teaches the reformist convention, be aware of the difference.

Question 2: How Are Directions Read? — By the Absolute Compass

“The auspicious sector is Southeast” means the absolute compass direction — unchanged by hemisphere: Sydney’s southeast is wherever the compass says southeast is.

One perceptual trap: in the southern hemisphere the midday sun sits in the north. If you habitually estimate direction by the sun (“sun side = south”), it inverts down under — trust your phone’s compass instead.

Question 3: True Solar Time? — Applies as Usual, Two Notes

The True Solar Time formula is global (full explanation). For southern users:

Enter longitude normally: Sydney at 151.2°E is 151.2, Auckland at 174.8°E is 174.8 (positive east values; latitude does not affect the time math);
DST straddles the new year: south-eastern Australian states observe DST from the first Sunday of October to the first Sunday of April — apply the rollback when manually converting birth times (details); Queensland, WA and NT observe none.

Southern City Longitudes

City	Longitude	City	Longitude
Sydney	151.21	Perth	115.86
Melbourne	144.96	Auckland	174.76
Brisbane	153.03	Wellington	174.78

In Practice

For a present-moment chart: open the charting tool, tap GPS (Sydney is also in the city presets) and let the engine handle the rest. For natal charts: recover standard time using that year’s DST rule first, then correct for longitude. And if you follow the reformist solar-term school, tell the AI mentor your convention in the chat — it can discuss the chart within your framework.