This article will explain how to catch the legendary Pokemon Solgaleo in Pokemon Sun. This article will also contain details on how to catch Cosmog after completing the main storyline.
How to catch Solgaleo
Source: http://www.pokemon.co.jp/ex/sun_moon/
Solgaleo can be encountered after defeating Lusamine in Ultra Dimension. After defeating her and returning to the real world, Solgaleo will be there. Talk to Solgaleo to battle against it.
If you defeat Solgaleo, you will be sent back to face it again and the story will not progress. Therefore, you need to catch Solgaleo.
After completing the main storyline, you will be able to obtain Cosmog which can evolve to either Solgaleo or Lunala. Because of this, there is no need to hunt for the perfect individual at this stage.
Since you will only encounter these Pokemon after defeating Lusamine in Ultra Dimension (which is already significantly further into the game), it will take a lot of time if you decide to hunt for the perfect individual here.
How to obtain Cosmog after clearing the main storyline
Source: http://www.pokemon.co.jp/ex/sun_moon/
After finishing the main storyline, put Solgaleo or Lunala in your party and head to a rift in space that which can now be found at the Altar of the Sunne or the Altar of the Moone.
Then, Ride your Charizard and fly to Route 16. and go through Ula’Ula Meadow until you reach the Lake of the Sunne or the Lake of the Moone. An event will occur.
After the event, you will obtain Cosmog.
For more details on how to obtain Cosmog, please see this article.
In pokemon sun is the rift in space in nighttime and in moon on daytime.