Sometime in the past fifty years, astrology-related flirtation went from ‘Hey, baby, what’s your sign?’ to ‘So, what time exactly were you born?’ Thanks to the Internet, it’s easier than it’s ever been to pull up your crush’s entire birth chart online and see how it compares to your own. I’ll let you decide if this is a good thing or a bad thing.

But our fascination with astrology is nothing new. Humans have charted the movements of the Sun and Moon as far back as the Stone Age. Experts disagree on when precisely ‘Ooh, look at the Moon!’ turned into using the planets to predict the future, but it’s clear that the practice has been around for thousands of years. Modern astrology dates back to ancient Babylonian times, with the first references to it arising somewhere in the second or third millennium BCE and the first recorded birth chart appearing around 410 BCE; Chinese astrology dates back even earlier.

In fact, astrology is so old that when it began astrologers believed the Earth was flat. And although we’ve long since learned better, astrology still charts the movement of the planets as they appear from our perspective on solid ground. When we talk about ‘Mercury retrograde’ – the much-hyped period of time when Mercury wreaks havoc on our lives by messing up our technology, causing us to miscommunicate and prompting our exes to send us a 2 a.m. ‘sup?’ text – we’re referring to when Mercury is moving backwards in its orbit from our point of view on Earth. Mercury isn’t suddenly defying the laws of gravity and reversing its course around the Sun; its apparent backwards motion is a trick of perspective caused by the different speeds of Mercury’s and Earth’s orbits. Have you ever looked out of the window in a fast-moving car and seen a slower-moving car appear to move backwards? Yeah, it’s like that. (If you try this at home, have someone else drive – and watch the speed limit!)

So, does this mean that astrology is fake? I’ve broken my phone or missed my train during Mercury retrograde too many times to say yes. But, in my opinion, ‘Is astrology real?’ isn’t the point – the planets don’t care what you think about them. You don’t have to believe that your day-to-day life mirrors the movements of the Universe to find astrology a useful tool in your life, or even just an interesting subject. Astrology has been around literally for millennia, through countless ebbs and flows in perceived legitimacy and popularity in different cultures and different interpretations. So, if you ask your next Tinder match what their sign is and they’re all, ‘Why do people believe in that junk?’ – well, astrology will survive long after you’ve forgotten they existed. (Also, don’t bother arguing; just unmatch them. Or, if you want to have fun, just say, ‘Oh, you must be a Capricorn’.)

You probably first became familiar with astrology through horoscopes – looking up your sign in a newspaper or magazine to see what might happen that day/week/month. But your sign is just one part of your birth chart. Although it’s often called your ‘star sign’, the proper astrological term is your Sun sign. It’s determined by the placement of the Sun when you were born. But you also have a sign describing where the Moon was when you were born, and Mars, and Venus, and Jupiter, and every other planet in the sky – not to mention asteroids like Chiron and mathematical points like the Nodes of Destiny (see here if you can’t wait to find out what these are). Yeah, it’s complicated! The more you learn about astrology, the more there is to find out – if there’s a point where you know it all, I’m certainly nowhere near finding it.

Astrology can be used to predict your future, yes, but it can also be used to help you understand yourself. I’m a Scorpio, an intense sign that represents sex, death, transformation and the occult. But as a shy, awkward pre-teen first learning about astrology, I thought that didn’t sound much like me at all. I felt more like a philosophical, travel-loving Sagittarius, the sign after Scorpio – and when I got older and learned more about astrology, I found out that my Moon, Mercury and Venus are all in Sagittarius, so my connection with that sign makes total sense (though these days I completely embrace my Scorpio traits).

In this book, you’ll learn the basics of reading your birth chart, and then go deep into the fun part: what astrology tells you about sex and compatibility. If you’re already an astrology know-it-all, feel free to skip ahead to Part III (to here, to be exact), but if you’re a newbie to the stars or just want a refresher, then this first section is for you. On the other hand, if you can’t wait to get to the sexy stuff, go for it and then come back to this part later to learn more about the nitty-gritty details.

Astrology contains a lot of its own language – words like ‘trine’, ‘mutable’ and ‘modality’. But while these words can be confusing at first, they’re usually used to describe fairly easy-to-understand concepts – and as you read more about astrology, you’ll probably find yourself using the lingo, too. If you get confused, though, take a look at the Glossary here – we’ve marked terms listed there in bold on their first use.