 Early radio telescope interferometers used a single baseline for measurement . Later astronomical interferometers , such as the Very Large Array illustrated in Fig 11 , used arrays of telescopes arranged in a pattern on the ground . A limited number of baselines will result in insufficient coverage . This was alleviated by using the rotation of the Earth to rotate the array relative to the sky . Thus , a single baseline could measure information in multiple orientations by taking repeated measurements , a technique called Earth @-@ rotation synthesis . Baselines thousands of kilometers long were achieved using very long baseline interferometry . 
