I would like to dig a little deeper for such a frivolous question as the definition of sign of the zodiac. Let's temporarily ignore the fact that "astrology is not science" and the sign of the zodiac "constellation".
Just try seriously to understand what factors must be considered to accurately determine in which constellation the Sun was at the time of birth.
the picture cosmopolitan.co.uk
Published real character horoscope with adjustments for precession, as of 2016:
Capricorn: January 20 — February 16
Aquarius: February 16 — March 11
Pisces: March 11 — April 18
Aries: April 18 — may 13
Taurus: may 13 — June 21
Gemini: June 21 — July 20
Cancer: July 20 — August 10
Leo: August 10 — September 16
Virgo: 16 September — 30 October
Libra: October 30 — November 23
Scorpio: November 23 — November 29
Ophiuchus: November 29 — December 17
Sagittarius: December 17 — January 20
This is all great, but what about those who are born in the transition day, for example, on September 16? He Leo or a Virgo?
The border between the constellations held by the circles of the celestial sphere straight climbs and arcs of declination in the Equatorial system of celestial coordinates. In this picture they are marked with red dotted lines.
Of course, the Sun crosses the constellation boundaries are not exactly at midnight or noon. The exact time of the transition varies from year to year, mostly due to the fact that in the year a non-integer number of days and there are leap years, and of the precession does not sleep.
For example, this year the center of the solar disk crossed the border of the constellations of Leo and Virgo 16 September at 15:40 Moscow time:
And in 2017, this event will occur in 21:24 Moscow time:
Moscow time... Hell, we have time zones to consider! Harder and harder.
And you can still remember that because of the parallax transition happens at different times for observers in different hemispheres.
The earth moves around the Sun at an average speed of 30 km/s, so the path is equal to its diameter (12 742 km), it takes 425 seconds. The difference can be up to seven minutes!
The earth moves around the Sun not the only one, it is accompanied by the Moon. In fact, the orbit does not move the Earth itself, and the center of mass of the system. The example of Pluto and Charon is clearly seen as the largest moon affects the position of the planet:
For the couple Earth-Moon this effect is smaller, but it's there and it should be taken into account. The new moon of the Earth moves faster than in the full moon. The moon then customize, then slows down our planet in its orbital motion. As for the year the Moon makes a non-integer number of revolutions around the Earth, its influence in every given day is different.
So, to determine the exact sign of the zodiac, need to know the exact minute of the birth time in UTC and the geographical coordinates of the hospital! How to determine the exact time of birth? The birth process is not instant... it Seemed to head? All the kid got? You cut the cord? Cried? But if a C-section? The doctor is a little sluggish, and here we have not a Leo, and Virgo.
There is a theory that the zodiac signs are determined "at the projection date of conception". Here, too, it may be difficult c accurate time.
Due to the finite speed of sperm, ejaculating does not coincide with the moment of conception. It may take a few days until one of the spermatozoa will reach the egg.
Stunning illusion with the dots that it is impossible to see simultaneously10 exercises for the brain, which stimulate the development of new nerve connections
Back to the heavens. Constellation boundaries are not tied to any real objects in the sky. They are where they are because "so agreed". Clear and unambiguous boundaries between constellations were adopted in 1928 by decision of the General Assembly of the International astronomical Union. For several years has been clarified. In 1935, astronomers finally agreed that the more change they will not. The person born in this troubled time, will have to raise the archives astronomical Union to define what the boundaries were in force at the time of his birth.
In General, I come to the conclusion that you can't give a definite answer to the question posed in the title. It's time to finish the article, let's discuss in the comments what else to consider.published
The article used the illustration xkcd.com available under CC-By-Nc.