Summer Resolution

Astronomers agree that the faintest objects the unaided human eye can see are stars of the sixth magnitude. (Magnitude decreases as brightness increases: a fifth-magnitude star is roughly 2.5 times brighter than a sixth-magnitude star; a fourth-magnitude star is 2.5 times brighter still.) That limit makes the famous globular star cluster in Hercules, which is overhead these nights, a fine eye chart: it beams in at magnitude 5.8. Another test is offered by the Big Dipper, now high in the northwest. Try to see any stars within the Dipper’s bowl--several hover just around the magnitude 6 barricade.