Zodiac Sign Dates: When Each Sign Starts

Zodiac sign dates are astronomical, not administrative. Each sign covers exactly thirty degrees of the circle the Sun appears to travel against the stars over a year, and a sign begins at the instant the Sun reaches its opening degree. Because a year is not a whole number of days, that instant lands at a different clock time each year, which is why one list prints a boundary on the 22nd and the next list prints the same boundary on the 23rd.

The dates a typical year follows

The table below holds for most years and is never more than about a day out. It is drawn for Greenwich, and the reason that qualification matters is covered further down.

• Aries. 21 March to 19 April
• Taurus. 20 April to 20 May
• Gemini. 21 May to 20 June
• Cancer. 21 June to 22 July
• Leo. 23 July to 22 August
• Virgo. 23 August to 22 September
• Libra. 23 September to 22 October
• Scorpio. 23 October to 21 November
• Sagittarius. 22 November to 21 December
• Capricorn. 22 December to 19 January
• Aquarius. 20 January to 18 February
• Pisces. 19 February to 20 March

If your birthday sits three or four days inside a range, the table settles the matter and nothing else is needed. If it falls on a listed boundary or one day either side, keep reading, because a table on its own cannot answer you honestly.

Where the day of slippage comes from

One trip around the Sun takes roughly 365 days and six hours. A calendar year holds 365 days. So in each ordinary year the Sun reaches the start of Aries about six hours later by the clock than it did twelve months before, and after three years that delay has grown to eighteen hours. The leap day on 29 February then shunts the calendar forward and the crossing snaps back to close to where it started.

The result is a four-year sawtooth rather than a slow permanent drift. Inside that pattern, a boundary falling late in the evening of one date in one year falls in the small hours of the next date three years later. Nothing has moved in the sky. The calendar has simply run a few hours ahead of it, or a few hours behind.

Four boundaries the sky sets exactly

Four of the twelve starting points are not conventions at all. They are events an observatory can publish to the minute, and everything else is measured out from them.

Aries opens at the March equinox, the moment the Sun crosses the celestial equator travelling north and day and night run close to equal length across the planet. Cancer opens at the June solstice, when the Sun reaches its furthest point north. Libra opens at the September equinox and Capricorn at the December solstice. The remaining eight boundaries divide the gaps between those four into even thirty-degree steps.

That anchoring also settles a question readers in Australia, South Africa and Argentina ask constantly. Sign dates are identical worldwide. They are fixed by where the Sun sits on its yearly path, not by the local weather, so Aries still begins at the March equinox in the places where that equinox opens autumn rather than spring.

Why the signs are not equal in days

Thirty degrees each does not mean thirty days each. The orbit of the Earth is a slight ellipse, and the planet moves fastest when it is closest to the Sun, in the first days of January. Seen from the ground, the Sun therefore appears to hurry through the signs it occupies at that end of the year and to dawdle through the ones opposite.

Sagittarius and Capricorn are the briefest, running a little over twenty-nine days. Gemini and Cancer are the longest at a little over thirty-one. Nearly two days separate the shortest sign from the longest, which is a second reason a single tidy list can only ever be an approximation.

The time zone changes the date

A boundary happens at one instant for the whole planet, but the calendar date attached to that instant depends on where you are standing. Say the Sun reaches the first degree of Taurus at eleven at night in London on 20 April. In Tokyo, eight hours ahead that month, the same instant is seven in the morning on 21 April. A baby born in Tokyo at three that morning arrived before the crossing and is an Aries, even though every list in circulation says Taurus began the previous day.

Published tables are almost always drawn for one time zone and hardly ever say which. This is the third source of the small disagreements between them, and it is the one readers least expect to find.

When your birthday lands on a boundary

Three plain things make the lists differ: the year, the time zone and the rounding to whole days. None of them is a disagreement about astrology. All three disappear the moment you stop reading across a table and work out where the Sun actually stood on your own date, at your own hour, in your own place.

Birthdays that land on a boundary have a folklore of their own, the notion that you belong to both neighbouring signs at once. That idea has its own guide here and deserves the space. As far as the sky is concerned the Sun occupies one sign or the other at any given second, and for a boundary birthday the only way to know which is to check your particular year rather than a general table.

One last thing worth saying plainly. Knowing the correct sign matters because everything written for that sign is written on the assumption you were placed in it correctly. Someone who has spent years reading Libra material while the Sun was in fact still in Virgo at the hour of birth has not learned anything false about Libra. They have simply been reading about a stranger.