TITLE: GCN CIRCULAR NUMBER: 18342 SUBJECT: LIGO/Virgo observing run 1 (O1) starts 2015-09-18 15:00 UTC DATE: 15/09/20 01:57:10 GMT FROM: Marica Branchesi at LSC Dear colleagues, We are pleased to announce that the O1 observing Run is starting today *Friday, Sept 18 at 15:00 UTC,* with the LIGO Livingston and LIGO Hanford detectors. At this time, the automated EM alert system is not in place yet. We will however do our best in sending out alerts for all coincident triggers at the agreed-upon false alarm rate threshold of 1/month, following the recent example. We will inform you as soon as we have the automated alert system set up. We are looking forward to collaborating with you during this exciting first advanced detector observing run. Best regards, Marica, Leo, and Peter [GCN OPS NOTE(19sep15): This Circular was originally published on 15:04 18-Sep-2015 UT.]