Differences
In contrast to radio arrays, the largest optical arrays currently have only 6 telescopes, giving poorer image quality from the 15 baselines between the telescopes. Most aperture synthesis interferometers use the rotation of the Earth to increase the number of different baselines included in an observation (see diagram on right).
Taking data at different times provides measurements with different telescope separations and angles without the need for buying additional telescopes or moving the telescopes manually, as the rotation of the Earth moves the telescopes to new baselines.
The use of Earth rotation was discussed in detail in the 1950 paper A preliminary survey of the radio stars in the Northern Hemisphere. Some instruments use artificial rotation of the interferometer array instead of Earth rotation, such as in aperture masking interferometry.
Read more about this topic: Aperture Synthesis
Famous quotes containing the word differences:
“Quintilian [educational writer in Rome about A.D. 100] hoped that teachers would be sensitive to individual differences of temperament and ability. . . . Beating, he thought, was usually unnecessary. A teacher who had made the effort to understand his pupil’s individual needs and character could probably dispense with it: “I will content myself with saying that children are helpless and easily victimized, and that therefore no one should be given unlimited power over them.””
—C. John Sommerville (20th century)
“Toddlerhood resembles adolescence because of the rapidity of physical growth and because of the impulse to break loose of parental boundaries. At both ages, the struggle for independence exists hand in hand with the often hidden wish to be contained and protected while striving to move forward in the world. How parents and toddlers negotiate their differences sets the stage for their ability to remain partners during childhood and through the rebellions of the teenage years.”
—Alicia F. Lieberman (20th century)
“Generally there is no consistent evidence of significant differences in school achievement between children of working and nonworking mothers, but differences that do appear are often related to maternal satisfaction with her chosen role, and the quality of substitute care.”
—Ruth E. Zambrana, U.S. researcher, M. Hurst, and R.L. Hite. “The Working Mother in Contemporary Perspectives: A Review of Literature,” Pediatrics (December 1979)