Where the Sun stands
At noon in every year from 1930 to 2035, the Sun on 7 May falls between sixteen and seventeen point four degrees of Taurus. That places it in the second decan, the band from ten to twenty degrees, with a margin of several degrees at both edges. No year in the range moves it out.
The reason the figure is so stable is the leap year cycle. A common year is about a quarter of a day short of the Sun's return, so the position advances slightly each year and a leap day pulls it back, keeping the drift inside a band roughly a degree and a half wide.
So the sign is settled and the decan is settled. What is not settled is which planet the tradition says governs that decan.
The Chaldean count
The Chaldean order runs Mars, Sun, Venus, Mercury, Moon, Saturn, Jupiter and then repeats. It starts at zero degrees of Aries and continues through all thirty six decans without a break, ignoring sign boundaries entirely.
Counted that way, the three decans of Aries take Mars, Sun and Venus, the first of Taurus takes Mercury, and the second of Taurus takes the Moon. So under this scheme a 7 May Sun sits in a lunar face. The tradition reads that as adding receptivity and a pull towards the familiar to a sign already described as settled.
The sequence is worth checking for yourself rather than accepting: it is a simple repeating cycle of seven planets over thirty six decans, and it produces the same answer whenever it is counted correctly.
The triplicity count
The triplicity scheme is built on a different principle. It gives each decan of a sign to a sign of the same element, taken in order. The earth signs are Taurus, Virgo and Capricorn, so the decans of Taurus go to Taurus, Virgo and Capricorn in that sequence.
The second decan therefore belongs to Virgo and, through Virgo, to Mercury. The reading that follows is quite different: analytical, exacting, and attentive to detail rather than to comfort, which is not obviously compatible with the lunar version. Neither scheme is a corruption of the other. They were built for different purposes and both survived, which is why published decan rulers conflict so often and why a source that names a planet without naming the method has left out the part you needed.
Beneath the argument, the same open questions
Whichever face you accept, the date settles the Sun and nothing more. The Moon changes sign about every two and a half days, so a 7 May birth has two candidate Moon signs and the hour decides. The Ascendant changes sign every couple of hours and depends on latitude as well, so all twelve remain possible.
That ordering is the point. The sun sign is what a birthday gives you and it is the coarsest layer of a chart, shared with everyone born in the same month, while the two placements that would narrow it need an hour and a place. The widget above computes the exact solar degree from your own year and birthplace and reports how far you were born from the nearest sign boundary. It works from an actual position rather than from a table of date ranges, so the figure it returns is the one the decan question turns on.
Questions people ask about this
What is the decan ruler for 7 May?
The Moon under the Chaldean order of faces and Virgo, meaning Mercury, under the triplicity scheme. Both are traditional, so the honest answer names the scheme along with the planet.
Which scheme is correct?
Neither is a mistake. They were constructed on different principles, the Chaldean on a repeating planetary sequence and the triplicity on elemental grouping, and both remained in use.
Is 7 May definitely Taurus?
Yes. The Sun is about seventeen degrees into the sign at noon in every year from 1930 to 2035, well clear of the boundaries on either side.
What degree is the Sun on this date?
Between sixteen and seventeen and a half degrees of Taurus, depending on the year and hour. The widget above returns the exact figure for a given birth.
Do decans change the sun sign?
No. A decan is a subdivision inside a sign, so the sign is unaffected. The decan adds a second ruler on top of the sign ruler in the schemes that use them.
Does everyone use decans?
No. Some schools give them considerable weight, others treat them as an optional refinement, and some ignore them altogether. The measurement is exact regardless of what is made of it.