The arithmetic behind the steadiness
The tropical year, the time the Sun takes to return to the same point relative to the equinox, runs to about three hundred and sixty five days and just under six hours. A common calendar year of three hundred and sixty five days is therefore short, and the Sun arrives at 6 May roughly a quarter of a day further along its circuit each year.
A quarter of a day is close to a quarter of a degree of solar motion. After three common years the position has advanced by about three quarters of a degree, and then February gains a day and the whole accumulated slip is handed back at once. The pattern repeats, so the position oscillates rather than drifting, and the band it oscillates in is about a degree and a half wide.
That is the whole mechanism. There is nothing further to it, and it is the reason a printed table of sign dates works well in the middle of a sign and fails at the edges.
Why it does not slip over centuries
Four quarters of a day are a little more than the shortfall, so the simple leap rule slightly overcorrects. The Gregorian calendar handles that by skipping the leap day in three century years out of four, which trims the excess and keeps the alignment good to a day or so over many centuries.
This is why a range measured across 1930 to 2035 can be quoted as though it applied generally. It is not a snapshot of one era. A birth in 1930 and a birth in 2035 on this date sit within a degree and a half of each other, and the same would hold for births a long way outside that window.
What that position means in the sign
Sixteen degrees of Taurus is comfortably inside the second decan, the band from ten to twenty. The Chaldean order of faces assigns it to the Moon, counting Mars, Sun, Venus, Mercury, Moon, Saturn and Jupiter unbroken from the start of Aries. The triplicity scheme assigns it to Virgo, dealing the earth decans out to Taurus, Virgo and Capricorn in order.
Above the decan sits Venus, the classical ruler of Taurus, and the sign is read as fixed earth: settled, attached to the tangible, slow to be moved. That is the tradition's reading, and it is offered as such. The measurable claim on this page is the position, not the description.
Sixteen degrees also sits several degrees clear of both edges of the decan, so unlike a birthday at the end of April this one needs no calculation to place its band.
Where the precision runs out
Solar positions behave well because the Sun moves slowly and evenly. The Moon does not. It covers about thirteen degrees a day and changes sign every two and a half days, so a 6 May birth has two candidate Moon signs and the date alone cannot choose. The Ascendant moves faster still, all twelve signs in a day, so the date says nothing about it whatsoever. Latitude complicates it further, since the signs rise at markedly uneven rates away from the equator.
The sun sign is the placement a calendar date pins down, and it is also the least individual thing in a chart. The widget above computes your exact degree from your own year and birthplace rather than assuming noon, and reports how far the birth stood from the nearest sign boundary.
Questions people ask about this
What degree is the Sun on 6 May?
Between fifteen and sixteen and a half degrees of Taurus across the last century. Your own value depends on the birth year and hour, and the widget above computes it.
Why does the degree stay so consistent?
Because leap years keep the calendar aligned to the orbit. The Sun slips about a quarter of a day further along each common year, and a leap day returns the accumulated slip, so nothing builds up.
Is 6 May always Taurus?
Yes, at noon in every year from 1930 to 2035, and at every hour. The nearest sign boundary is a fortnight of solar motion away.
Does the century year rule affect my birthday?
Not noticeably. Skipping the leap day in three century years out of four keeps the long term alignment steady, and the effect on any single birthday is a fraction of a degree.
Which decan is this and who rules it?
The second decan of Taurus. The Chaldean order names the Moon, the triplicity scheme names Virgo, and both are traditional, so the scheme should be stated alongside the ruler.
Do the same rules make Moon positions predictable by date?
No. The Moon moves roughly thirteen times faster than the Sun and its cycle does not fit the calendar, so a date narrows the Moon sign to two possibilities at best.