It is rare when we highlight a celestial event (or events) that involves the zodiacal constellation of Cancer the Crab. In Greek mythology, Cancer was summoned to distract Hercules when he was battling the multiheaded Hydra the Serpent. The crab was crushed by Hercules' foot, but to reward his effort Hera placed it among the stars.
One of my astronomy mentors, the late Dr. Ken Franklin of New York's Hayden Planetarium, used to refer to Cancer as "the empty space" in the sky. Indeed, it's the least conspicuous and second smallest of the 12 zodiacal constellations and quite frankly, aside from being in the zodiac, it's probably noteworthy only because it contains one of the biggest and brightest open star clusters in the sky. More on that in a moment.
