For the first gravitational wave detection in 2015, two gravitational wave observatories were up and running: The LIGO facility in Livingston, Louisiana, USA and the LIGO facility in Hanford, Washington, USA. The Livingston facility detected the wave seven milliseconds (0.007 s) before the Hanford facility. Now take a look at the map below. QUESTION: What does this observation mean about the location of the source? It came from the southern sky and traveled basically northward It came from the northern sky and traveled basically southward It came from directly above or directly below the red line indicated on the map below and traveled directly through the USA “down” It came exactly from the direction indicated by the white arrow EXPLAIN: IMAGE SOURCE: Another added feature is that gravitational waves, like EM waves, are the “transverse” – compression/elongation is perpendicular to the direction that the wave is travelling. So if a gravitational wave were coming out of the page towards you (or going directly into the page), it would result in the following behavior (definitely not to scale): One arm elongates while the second arm shrinks. Then both arms return to Then the first arm shrinks while the second elongates. Then both return to “normal.” normal. Then the cycle repeats as long as gravitational waves are coming through the detector.
For the first gravitational wave detection in 2015, two gravitational wave observatories were up and running: The LIGO facility in Livingston, Louisiana, USA and the LIGO facility in Hanford, Washington, USA. The Livingston facility detected the wave seven milliseconds (0.007 s) before the Hanford facility. Now take a look at the map below. QUESTION: What does this observation mean about the location of the source? It came from the southern sky and traveled basically northward It came from the northern sky and traveled basically southward It came from directly above or directly below the red line indicated on the map below and traveled directly “down” through the USA It came exactly from the direction indicated by the white arrow EXPLAIN: IMAGE SOURCE: Another added feature is that gravitational waves, like EM waves, are “transverse” – the compression/elongation is perpendicular to the direction that the wave is travelling. So if a gravitational wave were coming out of the page towards you (or going directly into the page), it would result in the following behavior (definitely not to scale): One arm elongates while the second arm shrinks. Then both arms return to “normal.” Then the first arm shrinks while the second elongates. Then both return to normal. Then the cycle repeats as long as gravitational waves are coming through the detector.