In addition to the Adventure Week happening in Pokemon GO right now, Niantic announced a new event called Legendary Raid Hours.
Pokemon GO Legendary Raid Hours will be available every Wednesday evening throughout the month of June 2019. During the 1 hour period, fans will be able to battle Legendary Pokemon in Raid Battles.
Starting today, June 5th and June 12th at 6:00 PM to 7:00 PM (local time zone), Pokemon GO trainers around the world will be able to battle the Legendary Cresselia in Raid Battles. And on June 19th and June 26th at the same time mentioned earlier, Legendary Kyogre will be taking the spot for Raid Battles.
During the Legendary Raid Hours, the developer also confirmed that there will be an increased number of stars, so expect a full and tight action to take down a Legendary Pokemon.