Have you noticed that the Solstices occur on a different day each time and that the beginning and ending dates for zodiac signs are different depending on which book you read? Did you wonder why one year Cancer begins on the 21st and the next on the 22nd? This is because both solstices and sun signs relate to the Sun’s path along the ecliptic and the Sun doesn’t change from one sign to another at exactly midnight. See Kelly’s article below for a table that shows this better. These variable dates can be a concern if you are born on one of those days when the Sun is changed signs, sometimes you’ll hear it referred to as a cusp and people will say you aren’t really one or the other but that isn’t true. The Sun moves through all 30 degrees of one sign before passing into the next so even if you are born close to a boundary you’ll be either 29 degrees Cancer or even 0 degrees Leo. 0 degrees Leo is still Leo and an astrologer can easily look up your date in an ephemeris and tell which on side of the cusp you fall. Or you can check your own using the ephemeris links below.
Here is an Ephemeris to check your own birth date: Link Astro.com, Swiss Ephemeris Files
Here is a good article in which Kelly Surtees shows why these cusp dates may look confusing. Link: Kelly’s Astrology – Sun Changing Sign, Dates for 2015