What is the schedule for science runs of aLIGO (and VIRGO)? Advanced LIGO seems to operate only intermittently. Is there a schedule for at what times it will be able to register new gravity waves? Even if no formal schedule is available, what main factors determine the scheduling?

I suppose VIRGO in Italy, to get started in 2016, will operate mostly simultaneously with aLIGO. Or would its design require another type of schedule?
There is no set date due to the complexity of the machines and their upgrades but this is the closest you will get to an answer:


  O1 is planned to last for four months, closing mid-January 2016. Then work will start on upgrading the instruments for our second observing run, which is called O2; those upgrades will be informed by what we have learned about the instruments during O1. O2 will start in 2016 and last around six months. Hopefully, around this time Advanced LIGO will be joined by Advanced Virgo.


They have no fixed date for the second observing run (O2) but it should be up an running later this year (my guess would be June-July time).