A 19th century depiction of the constellation Hydra. (Image credit: Pictures from History/Universal Images Group via Getty Images) Spring is here and with it, a new set of sparkling constellations rises to prominence! But what are the stories behind these mesmerizing stellar citadels and how can you find them in the night sky? Humanity's relationship with the stars stretches back for several millennia. In the modern day, we know the bright specks of their light to be incandescent orbs of glowing plasma powered by nuclear fusion , but in ancient times, the true nature of these stellar lanterns was a mystery. Read on to discover the mythology underpinning four popular spring constellations, along with tips on how to find them in the night sky . Be sure to check out our roundup of the best smartphone astronomy apps if you're new to the night sky, which can help you find everything from galaxies and nebulas to constellations and individual stars in the night sky.…