https://www.gamespot.com/articles/get-double-xp-in-destiny-2-this-weekend-heres-how/1100-6455038/

Destiny 2 is adding a new way to earn double XP. The Clarion Call event, which was announced last week, goes into effect starting on November 17 at 10 AM PT.

To earn double XP in the Clarion Call event, you have to be in a clan, though if you're not already you can create or join one during the event and still get the reward. Once you're in a clan, fighting alongside teammates in activities will yield double XP toward bright engrams for Destiny 2 Season 1. The double XP event ends on November 20.