Astronomers grapple with cosmic puzzles both dark and light
Four hundred years ago, astronomy embraced all that was visible. For Galileo, looking through his primitive telescope, the vistas included jewel-like stars, mountains on the moon, moons orbiting Jupiter and the glow of comet tails.
Today astronomy is often about what cannot be seen. Astronomers have known for decades that stars and galaxies are mere baubles floating on a vast sea of dark matter. More recently, astronomy’s roster of Darth Vaders has expanded to include an even more mysterious force: dark energy, an entity that drives the universe to accelerate its expansion just when gravity’s tug ought to be slowing it down.