This light, pretty dessert can be made up to three days ahead.
chilled strained tangerine juice (from about 16 tangerines)
finely grated tangerine peel
Ice cream maker
Combine sugar and 3/4 cup water in small saucepan. Stir over medium heat until sugar dissolves. Increase heat and bring to boil. Transfer syrup to medium bowl and chill until cold, about 2 hours.
Add strained tangerine juice, Prosecco, and finely grated tangerine peel to syrup; whisk to blend well. Transfer mixture to ice cream maker and process according to manufacturer's instructions.
Transfer sorbet to freezer container. Cover tightly with lid and freeze until firm, at least 8 hours or overnight. DO AHEAD Can be made 3 days ahead. Keep frozen. Divide sorbet among wine goblets or dessert glasses. Serve immediately.