Some of the strongest and clearest constellations are seasonal. I have a particular fondness for Orion, a winter constellation in the northern hemisphere, and l

Some of the strongest and clearest constellations are seasonal. I have a particular fondness for Orion, a winter constellation in the northern hemisphere, and look at it often. The first time I travelled to the southern hemisphere and looked up to the night sky, it was full of unknown structures - but I also found my old friend Orion - upside-down. I turned my head to get the familiar feeling back. Obviously, it was not the stars but me that were upside-down - the most definite sign of Earth's shape I have ever seen. And yet, it is hard to grasp. The world looks the same, solid, flat and steady beneath me. It is rare to get a glimpse of the world's three-dimensionality. Usually we live in only 2.5d.