How we computed them
We did not count birth records: the figures come from the sky. For each body we took its real position from an astronomical ephemeris, the same calculation that draws your chart, as seen from the centre of the Earth in the tropical zodiac of Western astrology. We followed it from 1925 to 2025, and the share in each cell is the fraction of that time it spent in the sign.
For the rising signs we turned the sky through one full rotation at each city and checked the Ascendant every thirty seconds. The time each sign spends on the eastern horizon, as a fraction of the whole rotation, is its share.
The key assumption
A share of time equals a share of births only if births are spread evenly over that time. How close that comes depends on the body.
For the Moon it is nearly exact. The Moon stays in a sign about two and a quarter days and passes through all twelve every month, so any pattern in when people are born, by season or by decade, is shared out evenly among the Moon signs.
The rising sign is nearly exact too. Births are not spread evenly over the clock, but the sky above any given clock hour shifts day by day, so over a year every hour meets every rising sign in turn.
For the Sun and the slow planets the figures are approximate. In many countries births rise and fall with the seasons, in patterns that differ from place to place and have changed over time, so the true share of a Sun sign drifts a little from its time share. The slow planets stay years in one sign, and the number of births per year changed a great deal across the century: a sign that a slow planet occupied in years with many births covers more people than its time share suggests.
Why the Sun signs are not exactly equal
If the Sun moved at an even pace, each sign would hold exactly one twelfth of the year. It does not quite, because the Earth's orbit is slightly oval. The Earth is closest to the Sun and moves fastest in early January, and farthest and slowest in early July, and from here the Sun seems to cross the zodiac faster or slower to match. So the Sun spends the least time in Capricorn, 8.1% of the years, a stay of just under 29 and a half days, and the most in Cancer, 8.6%, close to 31 and a half days. Sagittarius and Aquarius share Capricorn's 8.1%, while Gemini and Leo match Cancer's 8.6%.
Why the planets are uneven
Unlike the Sun and the Moon, the planets come out far from even, because their speed across our sky keeps changing.
Part of it is the shape of their orbits: a planet on a stretched orbit moves slowest on the side farthest from the Sun and lingers in the signs in that direction. Mercury spent 9.3% of the years in Sagittarius and only 7.5% in Gemini. Mars spent 10.0% in Leo and 9.9% in Virgo but hurried through Aquarius and Pisces, at 6.7% and 6.6%. Saturn held 10.8% in Capricorn and 6.4% in Cancer.
The rest comes from retrograde loops, when a planet seems to stop, back up and move on again, spending extra time over the same few degrees. Venus follows an almost round orbit, yet its loops keep returning to nearly the same parts of the zodiac, so it spent 9.8% of the years in Aries and only 7.1% in Libra.
For the outer planets a century is the wrong length to come out even. Uranus went all the way round and then crossed Aries and Taurus a second time, which gives those signs 15.0% and 14.1%. Neptune covered only part of the circle: it never entered Taurus, Gemini or Cancer in these years and reached Aries only at the very end, for 0.6%. Pluto moved from Cancer to Aquarius and was never in Aries, Taurus, Gemini or Pisces. Its orbit is so stretched that it crossed Scorpio, on the stretch nearest the Sun, in 11.4% of the century, and spent 18.6% in Leo.
Why rising signs change with latitude
The zodiac is tilted against the Earth's equator, so it meets the horizon at an angle that keeps changing through the day. Where the angle is shallow, a sign slips over the horizon quickly; where it is steep, the sign takes much longer. The further from the equator, the stronger the effect. In London, Aries rising clears the horizon in about 52 minutes a day and accounts for 3.6% of births, while Virgo rising takes 171 minutes, close to three hours, and accounts for 11.9%. New York lies further south and the range narrows, from 4.9% for Aries to 10.7% for Leo and Scorpio.
South of the equator the pattern reverses. In Sydney, Taurus and Aquarius rise slowest, 145 minutes each and 10.1% of births, while Virgo and Libra rise in about 80 minutes and account for 5.6% each. Aries, the rarest rising sign in London, reaches 9.9% there. The rising sign page explains the mechanism in more depth.
Citing the figures
Anyone may quote these figures, in an article or a lesson, with a link to this page. Keep in mind that they measure the sky, not people: a placement that is rare by these counts says nothing about how rare the person who has it is. To see where your own placements fall, the Big Three calculator finds your Sun, Moon and rising sign.