Few events herald the birth of spring like a shower of luminous pink petals falling softly from hundreds of cherry trees. Cherry-blossom viewing, known as hanami, is a centuries-old Japanese custom, a springtime occasion for merriment and the contemplation of life's beauty and transience. You can partake in this tradition at the Brooklyn Botanic Garden, home to scores of flowering varieties for public enjoyment. Guided tours focusing on the blooms are held on Wednesdays during the April viewing season, though the more-frequent garden highlights tours will touch on them as well. The month culminates in celebration of the brilliant blooms with Sakura Matsuri, a festival of Japanese performances and cultural happenings, on April 29 and 30.