OMG the world will be dark for 15 days what for and why is like its your question right. I can understand your eagerness to know about the topic recently on 15th Sep 2015 NASA said that the world will be experience darkness for 15 days and it starts for November 15,2015 at 3 am to November 30,2015 at 4:15 pm.
I know your question is Why is it happening ?
NASA say it is due to another astronomical happening between Jupiter and Venus.
There is result when Jupiter and Venus comes to so parallel to each other
1. Venus and Jupiter will come so parallel to each other, only being separated by 1 degree. Venus moves to the south-west of Jupiter causing Venus to shine 10 times brighter than the Jupiter. This will lead to a gaseous reaction.
2. The gaseous reaction releases enormous amount of Hydrogen into space which will make contact with Earth’s sun at 2.50 AM
3.The released hydrogen will cause a massive explosion on Sun’s surface making its surface temperature increase to 9000-degree kelvin in an instant.
4. Then Sun will attempt to cease the explosions by emitting heat from its core which will cause Sun to turn to bluish color.
5. It will approximately take 14 days for Sun to restore his surface temperature, returning its normal color to the red giant. While Sun is cooling the surface, the light from him will be much dimmer.
NASA has called it as #NovemberBlackout. It might be a hoax.