Heads up! If the forecast holds, the next three nights offer stargazers a tour of the western sky, guided by a slender crescent moon. Look west 45 minutes after sunset. Three days past "new," the moon stands tonight just to the right of brilliant Venus. Look again tomorrow and the moon will have passed left of Venus, approaching Saturn, the star-like object just to the moon's upper left. Tuesday, the fattening moon will crowd the bright star Regulus, 77 light years away in the constellation Leo.