Astronomically speaking, there is no "up"

 

Of course when we think about our immediate surroundings, the meaning of "up" is entirely clear. If you let something go and it falls, "up" is the other way. But suppose you back up and imagine yourself looking at the earth, the solar system, and what's beyond. Do you have an "up" in mind? I think most of us do. In diagrams, the solar system is always portrayed with the earth's north being up. There is no geophysical or or astronimical reason for thinking of things this way. Thinking of south being up makes just as much sense. The European cultures that dominated when we were standardizing our thinking about the geography of the earth and discovering details of the solar system were quite far north of the equator ("Greenwich mean time" is clearly UK-centric). North as up is a cultural decision. The fact that 90% of world population is estimated to live in the northern hemisphere would be a strong force against reversing that decision, but I suspect it did not actually have much influence on why it was chosen in the first place.

For me that is all old news. But I was surprised it took me so long to think of this next part... When you see a picture of some galaxy or other astronomical object, which way is "up"? Why is it oriented the way it is? It is not its relationship to the earth's north pole. The actual answer is that it is whatever direction the photographer chooses. It was one more tiny support for the reality of our planet being at an unremarkable spot in an unremarkable galaxy, and even "up" and "down" are arbitrary, even when we are looking out from our own particular world.