It's not September, it's the winter solstice, December 21'st. (Oh, it's also the Mayan Calender, not Aztec)
Fact
The Earth/Sun/Center of the Galaxy will all align on that date, no one really knows what this will cause, most likely nothing, but some scientists say a polar shift may occur.
Assumption
Mayans have oob3r hax and can predict when the world will end. The reason why some of this is believed is because they were able to accurately predict eclipses thousands of years in the future. Also, they supposedly made a prediction that white bearded gods would come upon their land, and on the exact date they predicted that, Spanish conquistadors came on their land.
False
Asteroid
The farthest observed asteroid is approximately 4,536,358,827,000 kilometers away. Now, assuming that this 'Death Roid' must be beyond this in order to be invisible, and that it is set to hit in 4 years, we can extrapolate a speed. 4,536,358,827,000 km/4 years.
1,134,089,706,750 km/year
8,760 hours/year
129,462,295 km/hour
1,079,252,848 km/hour (Speed of light)
12% SOL
So, the asteroid is going at about 1/8 the speed of light. Let's put this into perspective, shall we?
It's going 1,784 times faster than a supernova's explosion.
It's going 2,740 times faster than the fastest recorded asteroid.
It's going 334,652 times faster than a bullet.
I've heard reports that the size of the asteroid is near-earth sized. Let's assume this is an outlier, shall we? To accelerate the largest known asteroid towards Earth at that speed would require 940,050,815,664,960 newtons of force. That's 6,404,313 times the force of the Hiroshima bomb.