Ever notice how they're always playing golf on the show? That's because, as a poster named lostmio notes, golf is a great metaphor for why it's so hard to find the Island. Think of the golf course as the topography of 4D spacetime with the Island located in the hole. To get something to the Island with no temporal distortion takes the equivalent of a hole in one. If you're off by even a degree, you miss the hole completely, necessitating further strokes. The more strokes you take, the greater the temporal distortion. That's why Daniel is so insistent that Frank follow a precise bearing of 305.
That brings me to the purple sky. A poster named kansasgal speculates that the Orchid Station contains a particle accelerator capable of warping spacetime. One clue is Ben's Dharka with the Orchid logo. Another is the "frozen donkey wheel," supposedly the writers' code name for a big scene in the season finale. Kansasgal quotes one Dennis Mackey, who notes that the Large Hadron Collider, a massive particle accelerator in Switzerland, looks a lot like a donkey wheel and requires very low temperatures to operate. Like them, I believe the "frozen donkey wheel" is the particle accelerator in the Orchid.
Some scientists believe that the Large Hadron Collider may be capable of producing micro black holes. In Fixing A Hole, I described how the evaporation of these micro black holes yields Casimir force capable of warping spacetime. Another byproduct of their evaporation is high energy Hawking radiation -- hence the purple sky. The Casimir force generated by the frozen donkey wheel will reorient the Island randomly in spacetime, hiding it again from Widmore. That's why Ben checks with the hotel clerk what month and year it is after landing in the desert -- he's testing the effects of the event.
I further suspect that using the Frozen Donkey Wheel will do more than move the Island. The purple sky may also have implications for Michael, who has proven improbably impervious to death of late. Every time Iron Mike survives another brush with the Reaper, I'm reminded of Dan Simmons's description in Olympos of the Greek warrior Achilles as a freak of quantum probability:
"I see a quantum singularity," says the goddess Nyx. "A black hole of probability. A myriad of equations all with the same single three-point solution. Why is that, Artificer?"
The god of fire grunts again. "His mother, Thetis of the seaweed tangled breasts, held this arrogant mortal in the celestial quantum fire when he was a pup, little more than a larva. The probability of his death day, hour, minute, and method is one hundred percent, and because it cannot be changed, it seems to give Achilles a sort of invulnerability to all other attacks and injury."
To be clear, I'm *not* suggesting that the time of Michael's death is similarly set in stone. I do, however, believe these purple sky events function like the "celestial quantum fire," locking in certain probabilities along the timeline. Anyone who is present for such an event has a 100% chance of being there even if it means cheating death to make it. Take Charlie, who was present for the Swan implosion and accompanying purple sky. Before that event, he miraculously survived heroin abuse, a catastrophic plane crash, a cave in, and his hanging. Afterwards, by contrast, he couldn't die quickly enough...
I suspect the same may be true of Michael. Because he has a 100% chance of being present for the next purple sky, this grants him a kind of immunity from death until then. That's why he survived his suicide attempt, and why Keamy's gun repeatedly misfired. In each case, the universe course corrected to ensure Michael's survival, however slim the odds. But all bets are off once the purple sky occurs. As with Charlie, Iron Mike will be released from the grip of fate and free once again to die. Let us hope that he chooses to make his death a noble a sacrifice like Charlie's...