THE
DA R K
EN I G M A
Twenty years after
they discovered
cosmic expansion is
accelerating, astronomers
are still working hard
to understand why it's
happening.
14
M AY 2 0 1 8 * S K Y & T E L E S C O P E
Sky and Telescope - May 2018
Table of Contents for the Digital Edition of Sky and Telescope - May 2018