Orbiting Stars is a Path of Exile skill. orbs will rotate around the arena periodically firing projectiles at player location. Running through the Orbiting Stars will cause it to fall after a quick delay and explode, doing AOE damage.
Vorana, Last to Fall, the expedition boss, uses this skill.
During the fight with Vorana, in the outskirts of the arena will be little white stars which circle around, periodically shooting projectiles into the arena. As long as you do not come into contact with these stars they will not collapse. As the stars never enter the arena they are quite easy to dodge.
NOTE: Your minion can cause the stars to collapse too! So make sure to despawn your minion first etc golems when doing this challenge.
During the fight with Vorana, in the outskirts of the arena will be little white stars which circle around, periodically shooting projectiles into the arena. All you need to do is walk into 25 of these stars to collapse them. They will deal a small amount of area damage when they explode so try to keep moving, and being in the darkness will cause you to continually take damage, so try not to stay inside too long.
During the fight with Vorana, in the outskirts of the arena will be little white stars which circle around, periodically shooting projectiles into the arena. These projectiles can be slightly difficult to spot as they are small but if you keep an eye on where the projectiles are you can easily side-step them.