International Date Line International Date Line The International Date Line (IDL) is an imaginary line of demarcation on the surface of Earth that runs from the North Pole to the South Pole and demarcates the change of one calendar day to the next. It passes through the middle of the Pacific Ocean, roughly following the 180° line of longitude but deviating to pass around some territories and island groups. The IDL is roughly based on the meridian of 180° longitude, roughly down the middle of the Pacific Ocean, and halfway around the world from the Greenwich meridian. In many places, the IDL follows
Cygnus X-1 Sun. This implies that HDE 226868, Cygnus X-1 and this OB association may have formed at the same time and location. If so, then the age of the system is about . The motion of HDE 226868 with respect to Cygnus OB3 is ; a typical value for random motion within a stellar association. HDE 226868 is about from the center of the association, and could have reached that separation in about —which roughly agrees with estimated age of the association. With a galactic latitude of 4 degrees and galactic longitude 71 degrees, this system lies inward along the same