The night sky feels like a constant. Every night the constellations return in the same formation they have since we first began charting them. The planets were discovered simply because they were the only "stars" that moved in the night sky. Change happens very slowly in the universe and it is only through large passages of time that differences can be seen.
Most people already know that the sun will not remain the same forever. It is about halfway through its life cycle. The sun is currently about 4.5 billion years old, which means that in approximately 5 billion years it will have bloated into a red giant phase. As it heats up and expands, it will swallow the inner plants, including Earth. Only the inner planet Mars may be spared. By that time, we will have to have found a new place in the solar system (or beyond) if the human race is to survive. The sun will eventually shrink down into a cool white dwarf star, but by then Earth's water and atmosphere will be gone and it will be a lifeless rock.
But there is much more that will happen that earthly inhabitants can witness before the death of the sun. In only 50,000 years from now, the Big Dipper will become a strange new shape. The two stars farthest from each other, at the end of the handle and the outer and upper tip of the bowl, are not part of the cluster that the other Big Dipper stars belong to. These two stars will move away from the cluster, with the handle star moving downward and the bowl star moving straight out from the handle, giving the asterism a completely different look.
Another highly recognizable star pattern will also undergo changes. In the future, Orion will lose its brightest stars in explosions and new stars will emerge from the currently existing nebulas. The first to go will most likely be Betelgeuse, the red giant star marking Orion's shoulder. After Betelgeuse puts on its fiery show and then winks out, perhaps in 100,000 years from now, Rigel will have its turn. Rigel, marking the opposite corner of the constellation as Betelgeuse, will last possibly 1 to 2 million years before becoming a -9 magnitude object in the sky as it undergoes a nova and then settles into dim obscurity. But these stars will have been replaced by the newborn stars already forming in the dusty and gassy nebulas of the constellation. Both the Orion Nebula and Horsehead Nebula are creating new stars that will someday blow off the veiling dust and outshine their current dark cloak.
Also occurring before the sun swallows Earth in its red giant phase, will be the collision of Andromeda and the Milky Way galaxies. The first change seen from Earth will be Andromeda growing larger and brighter in the night sky. Andromeda is currently just barely visible to the naked eye from a dark-sky site, but a couple billion years from now it will be a large and bright target. But as it grows ever closer, it will begin to affect the stars in the Milky Way. These stars are currently seen in a limited swath across the night sky, but as the gravity of Andromeda distorts their paths, the stars will be flung across the sky. Earthly inhabitants won't witness a lot of fireworks due to stars colliding, because the stars in galaxies are so far apart that for the most part they will miss each other as the galaxies pass. However, gas clouds will likely collide, forming new stars. As the galaxies swing by they will be pulled back together again by gravity, and eventually settle down to form a new massive blob-shaped galaxy. By this point, Earth, the sun, and the rest of the solar system will have an entirely new home. We are currently about 25,000 light-years from the center of the Milky Way. After Andromeda and the Milky Way merge, we will have been stripped outward to 100,000 light-years from the center of the new galaxy. Theorist T.J. Cox of the Harvard-Smithsonian Center for Astrophysics calls it "a retirement home in the country."
These amazing sights are what awaits Earth or any solar system inhabitants. Our best chance of seeing something similar will be at a planetarium show, where we can sit in the dark and experience the new universe of the future.
