An equinox is the moment the Sun crosses the celestial equator, and a solstice is the moment it reaches its farthest point north or south of it. There are two of each every year. Around an equinox, day and night are close to equal in length almost everywhere; at a solstice, one hemisphere has its longest day and the other its shortest.
The tropical zodiac is built on these four points. The March equinox defines 0° Aries, the June solstice 0° Cancer, the September equinox 0° Libra, and the December solstice 0° Capricorn. Those four signs are the cardinal signs, traditionally linked with beginnings. The dates shift slightly from year to year, and the exact instant can fall on different calendar days in different time zones. Sidereal zodiacs use star-based reference points instead, so their sign boundaries no longer match these moments.
The astrology calendars list the four moments under equinoxes and solstices and name them by month, as the March equinox, June solstice, September equinox, and December solstice. Month names work in both hemispheres, whereas spring in the north is autumn in the south. Each event appears with its UTC time, alongside the other sign changes of the year.
For the circle the Sun follows, read about the ecliptic. The zodiac entry compares tropical and sidereal conventions, and the sign-boundary guide explains why the Sun’s entry into a sign does not come at the same clock time each year.
In a chart
A person born on the day of the June solstice may have the Sun in the last degree of Gemini or at 0° Cancer, depending on the time of birth. The solstice is the Sun’s ingress into Cancer, so a chart for that day needs the birth time before the Sun sign is certain. The same applies near the other three turning points.
Where you see it on Astrologican
These free tools and pages calculate or list it, so you can see it in a real result.