Because I mention it from time to time and I know nothing about it.*
If you're ever questioning whether or not Mercury is in retrograde this handy website dedicated to just that can help:
But what does that actually mean? Scientifically speaking, it is an occurrence that happens about 4 times a year when the planet Mercury appears to stop and move backward in the sky, hence the "retrograde" term. It's not actually moving backwards, but the speed of the Earth's rotation is faster than the speed Mercury is rotating around the sun. It's a cosmic optical illusion.
In terms of astrology, Mercury is the planet of communication. Much like its counterpart, Mercurius the Roman god, a parallel to the Greek god Hermes, he was the guy with the shoe-wings. He is the messenger between the heavenly and mortal worlds, and that's pretty important. Mercury represents the quick, cunning, restless nature of life. But most of all Mercury handles communication and transportation.
So, when the planet Mercury is in retrograde, these things get muddled. Much like the old saying that the full moon brings out the crazies, as does Mercury in retrograde. Communication will be fucked up. Planning trips or your daily commute might be difficult at this time. Tread lightly.
So that's a bit of what Mercury in retrograde represents. If you're the superstitious type, you might be weary that today is a full moon, and also happens to be Friday the 13th, and Mercury being in retrograde? That's the power of 3 working against you right there. So be careful.
*If I've messed up any facts or left something important out, let me know! I wrote this in a haste so your input is appreciated!! I'm not an expert and would never claim to be