Constellations are groups of stars that ancient astronomers connected into pictures, creating shapes like bears, ploughs, and chariots in the night sky. Different cultures shows the same stars in their own ways, and over thousands of years these shapes slowly change because the stars move across space. Today there are 88 official constellations, and although their patterns shift over time like Cassiopeia changing from a clear W to a more uneven line we still use them to understand the sky and imagine how they might look far into the future.