Make Corona Borealis is the 3rd bonus level in the game, and can be unlocked after beating the fifth main story level, Make a Star 5
To beat the level, you will need to collect 44 crowns. Just like the other bonus levels, they will be scattered about the map. Most of the crowns will be found on top of things, including people. It is crucial to gain enough mass to take down humans in the large area. Most will have crowns.
If you need a quick boost of crowns, located in the back of the big area is a farm. There will be a bush with a large golden crown. Right in front of is 6 white dots, each of which are crowns.
Hope this helps!