For a Dao Lord like Alkaid, the Northern Sea Star was merely a speck.
Whenever any two Dao Lords fought, the disturbances they caused in the Great Dao could be sensed by all Dao Lords on the Northern Sea Star.
Often, wide-scale confrontations between Dao Lords were avoided on the Northern Sea Star, due to the risk that it might shatter the star.
Even though...
the Northern Sea Star was influenced by the rules of the Gate of the Immortal Realm, which made it many times more robust than any other star.
Similarly, when a Dao Lord knew the destination of other Dao Lords, as long as the direction was correct, it was easy to wait on their inevitable path.
After all, to them, this "road" could be hundreds of thousands, even millions of miles wide.
That's exactly how Penglai Dao Lord intercepted them.