The Orion constellation can be clearly seen in the winter in the Northern Hemisphere. In the Southern Hemisphere, it's high in the night sky during the summer, but it appears upside down. (Image credit: wenbin via Getty Images) Some stars and constellations are ever-present in the night sky; Polaris, for example, has served as a steady guiding light for millennia in the Northern Hemisphere. But if you look closely at the sky night after night, you may notice that some stars move east to west from dusk to dawn, as well as change positions from season to season. For instance, Orion disappears from view for part of the year. So why do some constellations stay visible year-round, while others disappear and reappear depending on the season? To make sense of this, it's helpful to note that when we look at the night sky, we're viewing only a section of the universe.…