Here’s a fun bit of astronomy for all my friends in the northern hemisphere: In the southern hemisphere, the moon actually looks upside down!

Photo via Dr. Alex Kumar on Twitter.

But it is you that is upside down, not the moon. Let me explain. Let’s assume for the sake of this example that the moon orbits the earth around its equator. Let’s then have a girl in red stand in the northern hemisphere look at the moon and a girl in blue stand in the southern hemisphere and look at the moon:

Even though the girl in blue is standing at the “bottom” of the earth, because of gravity, which pulls her towards the center of the earth and gives the sense of “down,” and optics, she perceives what is at the top of her visual field as the “top” and what is at the bottom of her field as the “bottom.” Because the orientation of the moon does not change, this flip in perception makes the moon appear upside down.

Of course, it is an arbitrary decision to designate the northern hemisphere’s view of the moon as right side up. This probably stems from our North and South poles, and because north traditionally points upwards, we tend to view our celestial position in that frame.