The commonly held misconception is that being born on the cusp of two signs gives you a combination of traits from those two signs. According to the AstroTwins, the cusp theory developed "mainly because, in the 20th century, newspaper and magazine horoscopes became very popular" and introduced the ideas of cusps to the mainstream.

"Since the Sun changes signs at a different time each year, it can vary by a day or so. In order to help people decide which horoscope to read in these offerings, they approximated the date that the Sun would change to the next sign. Some years, Gemini season starts on June 20, others on June 21. Because there are 365 days a year and 12 signs, you can't evenly divide the year by 12 without having 5 days remaining."

Nevertheless, the AstroTwins don't subscribe to cusp theory—here's why.

"There is actually no such thing as cusps," the twins say. Due to the way the Sun transitions from signs, it's not possible to be under two at the same time. There is an exact moment when the switch happens.

Of course, that's not to say you can't have a combination of traits from different signs. After all, that's what your birth chart is all about. A Scorpio-Sagittarius cusp, for example, might actually be a true Scorpio, but perhaps their Venus is in Sagittarius. As far as the sign the Sun was under while transitioning from one to the next, though, it's never under both.