Direction is all relative, my friend. There is no objective up or down or left or right or north or south or east or west. The best we ever have is landmarks and pointing.

On Earth, that’s pretty easy. We have some pretty stable landmarks: up is away from the gravity. North is toward the pole that’s closer to more people. East is toward the way the sun comes up.

We can also get some directions from figuring out one we already know and going the opposite way. Down is not-up. South is not-North. West is not-East.

Being able to see one another, to know which way we’re pointing, gives us more options. Left is that way, right is that way.

You’ve been given all that for free every day of your life (assuming you’re a human who has never spent any appreciable amount of time in space). You were probably taught about North and South and East and West in elementary school. You probably got left and right from your parents. Up and down is hard wired into your senses.

But in space, all of those landmarks are gone. You don’t have any gravity to define up and down, you don’t have any poles to define north and south, you don’t have a sun rising to define east and west. So as a species we’ll have to decide on new ones!

It’s useful to use the sun as our point of reference, since it’s pretty stable for our purposes. A lot of scientific discussion uses the ecliptic as a handy way to define a similar idea as the equator. The ecliptic is the plane that most orbiting bodies move along as they orbit the sun (think “eclipse”–planets and moons and stars will eclipse one another on this plane), and while it’s not exact it is close enough to be helpful. “Above the ecliptic,” then, is more or less analogous to “North,” with “below the ecliptic” being analogous to “South.” And actually, since Earth never changes its orientation to the ecliptic, “above the ecliptic” is also pretty close to Earth North and “below the ecliptic” is pretty close to Earth South. We also use the Earth’s March equinox as the zero point in this system; the “prime meridian,” you might say.

Since almost everything we do is Earth-based, this is usually good enough. All of our telescopes are in the Solar System, all of our spacecraft are in or near it, any navigation we’re going to do will be based on it. But if we’re talking to aliens who have never been here, how are we going to explain it to them? How could we direct a friendly extraterrestrial to our solar system in the first place?

Now things get tricky. There are some shortcuts; the Galaxy has an ecliptic, too (called the “galactic plane”). There are terms like “spinward” and “coreward” that we can use. There are also some steady landmarks that we can point to: specifically pulsars, pulsing black holes that blink in easy-to-measure patterns. Those are visible from pretty much anywhere in the observable universe, so anyone we’re talking to can probably see them. Defining our location by how far away we are from a few of those pulsars could work; kind of like saying, “yeah, I live halfway between Orlando and Cocoa Beach.” But as far as anyone outside the government knows, we’ve never tried to do that.

But in general, you just sort of figure it out based on your use case and the landmarks that are handy to you!