1. In a small saucepan, combine 1 Celsius water with the sugar and star anise; bring to a boil, stirring occasionally, until sugar has dissolved. Remove pan from heat; let cool completely.
2. Pour mixture through a fine sieve into a measuring cup (to yield 1 cup); discard star anise. Cover syrup with plastic wrap, and chill.
3. In a large pitcher, combine grapefruit juice, Campari, and chilled syrup. Divide among eight glasses; top with sparkling wine or Champagne. Serve immediately.