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:
“The mother must teach her son how to respect and follow the rules. She must teach him how to compete successfully with the other boys. And she must teach him how to find a woman to take care of him and finish the job she began of training him how to live in a family. But no matter how good a job a woman does in teaching a boy how to be a man, he knows that she is not the real thing, and so he tends to exaggerate the differences between men and women that she embodies.”
—Frank Pittman (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)
“I trust the time is nigh when, with the universal assent of civilized people, all international differences shall be determined without resort to arms by the benignant processes of civilization.”
—Chester A. Arthur (1829–1886)