NOCTILUCENT CLOUDS: While you're out looking at the planets, be alert also for electric-blue noctilucent clouds. Olaf Squarra of Rostock, Germany, photographed these over the Baltic Sea on June 24th:

An 8-minute movie of the display shows how the clouds ripple and move like waves in the ocean.
Noctilucent clouds (NLCs) are a mystery. They hover near the edge of space, far above ordinary clouds. Some researchers believe they're seeded by space dust. Others say they're a sign of global warming. Whatever they are, they're beautiful, and northern summer is the best time to spot them.