Position and approximate dates
Twenty to thirty degrees is the final third of the sign. A placement here is described as late Taurus, and in traditional practice a planet in the last degrees of any sign is already partly oriented towards the next one.
The Sun passes through in about ten days, roughly 10 May to 20 May. As with every decan boundary, that shifts by up to a day and a half from year to year, because the calendar and the tropical year drift against each other and the leap day resets the drift.
Because the closing boundary is the start of Gemini rather than a solstice or an equinox, it drifts with the calendar in the ordinary way, without the extra anchoring that the cardinal points give to the decans that begin the seasons.
Two schemes, one answer
Counting the Chaldean order from zero degrees of Aries, the sequence Mars, Sun, Venus, Mercury, Moon, Saturn, Jupiter repeats through the thirty six faces. The sixth face, which is the last of Taurus, lands on Saturn.
The triplicity scheme takes a different route. Earth decans go to Taurus, then Virgo, then Capricorn in order, so the closing decan of Taurus is given to Capricorn. Capricorn's ruler is also Saturn.
Agreement of this kind is not the norm. Across the zodiac the schemes contradict each other more often than they match, and articles that name neither leave the reader with no way to tell whether a stated ruler is contested. Here it is not.
Capricorn material and the Saturn face
The Capricorn colouring is read as the Taurus concern with material security turned into something structured. Taurus alone is described as accumulating and keeping; with Capricorn mixed in, the tradition describes the same instinct organised into arrangements that outlast the moment, such as contracts, long employment or property held for decades rather than goods enjoyed now.
Saturn as face ruler is taken to add a specific quality of delay. Results are read as arriving late and then holding, which sources tend to phrase as slow to build, hard to dislodge. The stated cost is a reluctance to move on a decision until the ground has been tested more thoroughly than the situation requires, so opportunities with short windows can be lost.
Read this as the tradition's claim rather than as a prediction. What would change it in an actual chart is the condition of Saturn itself, its house and its aspects, none of which a decan page can know.
The saturnine reading is also applied to timing rather than to character alone. Traditional sources use faces when judging when a matter will resolve, and a Saturn face is taken to indicate later rather than sooner, which is a claim about pace and not about outcome.
Other placements, and checking the boundary
The technique is not restricted to the Sun. An Ascendant at twenty five degrees of Taurus sits in this face, and a Moon at twenty two degrees does too. Because the Ascendant advances by roughly a degree every four minutes, it is the placement where decan divisions do most to separate one chart from another.
Honest framing matters here. Decans descend from Egyptian star lists that once marked hours of the night, so the system is genuinely ancient, but in a working chart reading it sits well below the sign, the house and the aspects in importance. It refines a description that already exists.
Since a boundary is a degree rather than a date, the check above computes where your Sun actually stood. Anyone born near 10 May or 20 May will find that a published date range cannot answer the question and a computed degree can.
Questions people ask about this
What are the dates for the third decan of Taurus?
Roughly 10 May to 20 May. Boundaries move by as much as a day and a half between years, so a birth date at either edge needs a calculated degree rather than a table.
Who is the ruler of late Taurus?
Saturn, under both methods. The Chaldean count reaches Saturn on this face, and the triplicity scheme gives the last earth decan of Taurus to Capricorn, which Saturn rules.
Does Saturn here mean a hard life?
No, and the tradition does not claim that. It reads Saturn as slowing and consolidating, which is described as a delay in results rather than a verdict. Saturn's house and aspects in the actual chart change the reading considerably.
What is a decan?
A ten degree slice of a sign. Each sign holds three, giving thirty six across the zodiac. The divisions came from Egyptian star groups long before they were assigned planetary rulers.
Is this the same as the Taurus and Capricorn combination in a chart?
Not quite. The triplicity decan borrows Capricorn's flavour without placing anything in Capricorn. It is a colouring of a Taurus placement, not a second placement.
Do decans work for the Ascendant?
Yes. Any degree in the chart falls in a decan, and the rising degree is a common place to apply the technique because it changes fastest across the day.