⊕ Free Coalescent Relationship Chart Calculator
Umbriel computes the coalescent chart — a relationship chart built from the harmonic mean rather than the midpoint, which makes it a genuinely different construction from a composite. Free, with the composite and Davison alongside.
- What you'll needBirth date, time and place for both people
- What you getThe coalescent chart, and the composite and Davison beside it so three methods can be compared
- CostFree — no account required
Runs in your browser. Nothing to install, nothing to set up.
What it actually is
A coalescent chart combines two charts using the harmonic mean of their positions rather than the arithmetic midpoint a composite uses. Because those are different operations, it produces a genuinely different chart rather than a variation on the composite.
It is the least known of the three relationship-chart methods and the most recent. There is far less written about reading it than about composites, which is worth knowing before you lean on one — the technique is well defined and the interpretive tradition is thin.
The reason to compute it is comparison. Three constructions built on different arithmetic that nonetheless agree about something is a stronger signal than any one of them alone — and where they disagree tells you the agreement elsewhere was not automatic.
⚠️ With the same caution that applies to composites: outer-planet agreement between any two of these methods is largely arithmetic for any two people, and is not a finding about a relationship.
How Umbriel computes it
The coalescent is built from the harmonic mean of the two charts rather than the arithmetic midpoint a composite uses — a genuinely different operation that gives a different chart, not a variation on the same one. Umbriel computes it alongside the composite and the Davison so all three relationship methods can be seen together, since where three constructions built on different arithmetic agree is more interesting than any one of them.
What's in your result
- The coalescent chartBuilt from the harmonic mean, drawn as a wheel.
- Composite and Davison alongsideAll three relationship methods, side by side.
- Where the three agreeWhich is the only reason to compute more than one.
- Angles and housesBoth birth times required, as with the others.
- Aspects within the chartRead as the internal structure of the relationship.
Common questions
What is a coalescent chart?
A relationship chart built from the harmonic mean of two charts' positions, rather than the arithmetic midpoint used by a composite. It is a different calculation, not a variant.
How is it different from a composite?
The composite averages positions; the coalescent takes a harmonic mean. They give different charts. The composite has a much larger interpretive literature behind it.
Should I read the coalescent instead of the composite?
Probably not instead — there is far less written about reading it. Its value is mostly in comparison: three methods agreeing is more interesting than one method asserting.
Do both people need birth times?
Yes, for the angles and houses, exactly as with the composite and Davison.
Which relationship chart should I actually use?
The composite has by far the largest literature and is the usual starting point. The Davison appeals to people who want a real sky. The coalescent is the least written about. Umbriel computes all three because comparing them is more informative than trusting one.
Is the coalescent chart traditional?
No — it is a modern construction, and a recent one even by modern standards. That is worth saying plainly rather than letting it sit alongside Hellenistic techniques as though it had the same pedigree.
Is the coalescent calculator free?
Yes — all three relationship charts and the comparison between them, with no account.
Go deeper
Each of these is a free tool in its own right.
Umbriel offers every system here as a set of prompts to think with, never as a statement of fact about who you are. Take what's useful, leave the rest.