The last true Capricorn was born on 20 January 2024

Key findings

• Only 12.3% of the 309 million births in our data had the Sun in the constellation of their sign. Every Libra in our data had the Sun in Virgo, 99.9% of Geminis had it in Taurus, and 62% of Sagittarians had it in Ophiuchus.
• Almost three times as many people are born under Ophiuchus as under Scorpius. By constellation, 4.9% of births fall in Ophiuchus and 1.7% in Scorpius: the Sun crosses Scorpius in about 6.5 days and Ophiuchus in 18.3. Virgo is the widest, at 44.5 days.
• Four signs have already lost their constellation for good. Libra in 1438, Scorpio in 1926–27, Gemini on 21 June 1989 and Capricorn on 20 January 2024. Aries is next, around 2094. Leo holds out until about 2852, and from about 2854 nobody will be born in the constellation of their sign.
• In 2024 about a hundred to two hundred babies in our data were the last true Capricorns. All were born on 20 January 2024, in the minutes before 14:07 UTC: from 13:55 by the apparent Sun, from 13:47 by the geometric one (see Method). Worldwide, at some 250 births a minute, that is roughly 3,000 to 5,000 people. Ten years earlier Brazil, England and Wales, and France alone had 1,331.
• The signs never matched the constellations exactly. The best fit, by today’s boundaries, was around AD 1: the sign and the constellation agreed 83% of the year. Western astrology stopped tying its signs to the stars about two thousand years ago and counts them from the March equinox. The sidereal zodiac of Indian astrology still agrees with the constellation for 80% of births.

Your three signs

A birthday has three answers: the tropical sign of Western astrology (counted from the March equinox), the sidereal sign of Indian astrology (fixed to the stars, Lahiri), and the constellation the Sun was actually in. Enter a date from 1900 to 2100. The time is optional, but on the days when the Sun changes sign or constellation it decides the answer; pick the clock that was in use, summer time included.

The share of the trio comes from births in France, England and Wales, the USA, Brazil and Japan; the signs and constellations are computed for any date. Nothing leaves your browser.

Where each sign’s Sun really was

Each bar is one tropical sign, split by the constellation the Sun was in on those birthdays. The gold piece is the constellation with the same name. For most signs it is a sliver; for Libra it is nothing.

Thirteen constellations, very unequal

Along the Sun’s path the official boundaries cut thirteen constellations, not twelve, and their widths range from under a week to more than six weeks. Ophiuchus, the serpent-bearer, sits between Scorpius and Sagittarius and takes 18.3 days a year. Scorpius, squeezed in its corner, gets 6.5 days.

The “13th sign” is an old story that returns every few years. In 2016 a NASA page for children explained precession, headlines turned it into “NASA changed the zodiac”, and the agency answered that it had changed nothing and only done the arithmetic. The arithmetic is above. It is not new: Ophiuchus has been on the Sun’s path for as long as these boundaries have existed.

The last true one of each sign

The Earth’s axis wobbles slowly (precession), so every year the constellations slide about 20 minutes later against the signs. Each overlap between a sign and its namesake constellation therefore shrinks at the end of the sign by that much a year, until it closes for good. Here is when.

Two lengths, because there are two Suns to measure with (see Method): within one year the apparent Sun of astrology gives the shorter window, the geometric Sun, which reaches the catalogue line of the constellation about 8 minutes earlier, the longer. For Cancer, Aquarius, Virgo and Leo the geometric Sun keeps the overlap one more year, and the shorter length is that final window; for Scorpio and Aries the earlier of the two years comes from nutation, and both lengths are of the later one. Libra’s date is in the proleptic Gregorian calendar; Europe then used the Julian one, in which it is nine days earlier. Far in the past and after about 2500 the instant is uncertain by hours (the Earth’s rotation is not known that far), but not the year.

On 20 January 2024 the window closed at 14:07 UTC; it had opened at 13:55 by the apparent Sun and at 13:47 by the geometric one, and in Sydney it was already around 1 a.m. on 21 January. In our data that is about 90 in Brazil, 12 in England and Wales, 13 in France, and 12 in Japan by the first count, about 151 in Brazil, 20 in England and Wales, 21 in France, and 21 in Japan by the second: roughly a hundred to two hundred people, the last true Capricorns these countries will ever record. These are estimates. Except in Brazil, which records the hour of birth, we only know the day; Brazil’s window fell around 11 a.m., near the busiest hours of its birth day. The last true Geminis arrived on 21 June 1989: about 12 in France by the apparent Sun, 26 in France by the geometric one (our US series has a gap from 1989 to 1993).

Five thousand years of drift

Run the same boundaries backwards and the signs fit the constellations best around AD 1: 83% of the year. That is close to the time of Ptolemy, whose Tetrabiblos argued for counting the signs from the equinoxes and solstices, almost three centuries after Hipparchus discovered that the equinoxes move. Today the figure is 11%, and it reaches zero around 2854.

Why astrologers are not worried

Western astrology’s signs are twelve equal slices of the year, starting at the March equinox. They were named after the constellations nearby two thousand years ago, and they have followed the seasons, not the stars, ever since: Aries still begins the northern spring. Ptolemy knew about the drift and chose the seasons. Indian astrology made the other choice and keeps its signs fixed to the stars; that is why its sidereal sign matches the constellation for 80% of births in our data, and misses mainly where Ophiuchus and the unequal widths get in the way.

So the tables on this page do not move anyone’s sign. They answer a different question: where in the sky was the Sun when you were born? Your tropical sign answers “what season”, the sidereal sign “which stars, in twelve equal parts”, and the constellation “which official region of the sky”. A natal chart can be drawn in either zodiac.

Method

• The Sun. Swiss Ephemeris (Moshier), apparent position. The tropical sign is counted from the true equinox of date, the sidereal sign with the Lahiri ayanamsa, both as in our rarest-sign study.
• The constellations. The 88 official regions of Delporte (1930), bounded by arcs of right ascension and declination of the equinox B1875.0, looked up with the method and table of Roman (1987) as shipped with astropy. The Sun’s position is referred to the mean equator of date and precessed to B1875. A second precession route, written by hand from the IAU 1976 angles, gives the same constellation at 400 random instants within 30 seconds of a boundary. Between 1900 and 2100 the Sun crosses exactly the 13 constellations above, in order, and never Cetus.
• Births. Each local civil day’s births are split by the share of the day the Sun spent in each sign and constellation, with births uniform over the day; Brazil from 2006 is split by its recorded hours. On Brazil’s recorded hours, the uniform assumption moves a constellation’s share by at most 0.002 percentage points. The tropical counts reproduce our rarest-sign study exactly.
• Last overlaps. For every year from about 2900 BC to AD 2998 we test the Sun’s constellation one minute before it leaves each tropical sign, and report the last year in which it is still the namesake constellation, with the length of that last window. That length has two honest values. The Sun of this page is the apparent one, light-time and aberration included: the Sun of astrology and of the almanacs. The boundaries, though, are catalogue lines drawn on the mean places of the stars, which aberration does not shift, so a geometric Sun measured against them enters every constellation about 8 minutes earlier, and each last window is that much longer: Capricorn’s 12 minutes become 21. The table and the counts print both. Including nutation, or using the geometric instead of the apparent Sun, moves Scorpio, Aries, Cancer, Aquarius, Virgo and Leo by one year; those are printed as two years. Libra, Gemini, Capricorn, Sagittarius, Taurus and Pisces do not move. An independent recalculation with its own boundary polygons (CDS VI/49), precession and point test agreed within a minute on every end time and on every year except Aquarius (2179 there), which is printed as two years anyway.
• Over the centuries. The share of the tropical year with the sign in its constellation, sampled every 2.4 hours, every 10 years.

Limits

• These are births in France (1968–2024), England and Wales, the USA, Brazil and Japan in the years each publishes by day, not people alive today. The shares by constellation barely differ between them (the Sun’s calendar is the same everywhere; only the season of births differs).
• Counts of births inside one short window (the last true Capricorns and Geminis) are estimates: we know the day, and in Brazil the hour, not the minute. An independent recount of Brazil by the recorded minute gives 69 instead of 90, and Japan’s table of births by hour gives 8 instead of 12: read them as “about a hundred”, not as a count. The world figure assumes births spread evenly over the day.
• Every instant on this page, the calculator included, is by the apparent Sun. By the geometric Sun the entry into a constellation comes about 8 minutes earlier: each last window is longer by that much, the births inside it more numerous in proportion (127 against 213 last Capricorns in our data), and within those minutes of a boundary the calculator’s constellation depends on the convention. The years move by one at most, and where they do, the table prints both.
• The constellation boundaries are a convention of 1930. Any line drawn elsewhere would move every date on this page; we use the official one because it is the one everybody means by “the constellation”.
• Nothing here tests what signs say about people.

Sources

• INSEE, births by day, metropolitan France (T79JNAIS), Licence Ouverte. ONS, Births in England and Wales, table 12, births by day, OGL.
• United States: NCHS natality, births by day 1969–1988, via the Google BigQuery natality sample as published with A. Vehtari’s Birthdays case study; CDC births by day 1994–2003 and SSA 2004–2014 (FiveThirtyEight, CC BY 4.0).
• Brazil: SINASC, Ministry of Health / DATASUS, every live birth by date and hour (CC BY-ND 3.0: only aggregates are published here). Japan: Vital Statistics, e-Stat table 0003411915, births by day.
• Constellation boundaries: E. Delporte, Délimitation scientifique des constellations (IAU, 1930); N. G. Roman (1987), Identification of a constellation from a position, PASP 99, 695 (CDS catalogue VI/42). Ephemeris: Swiss Ephemeris; coordinates: astropy.