The diameter of the → primary mirror in a → reflecting telescope, the → objective lens in a → refracting telescope, the → dish of a → radio telescope, or the → entrance pupil of an instrument such as → spectrograph or → photometer.
From L. apertura, from apertus, p.p. of aperire "to open, uncover," from PIE *ap-wer-yo- from *ap- "off, away" + base *wer- "to cover".
Ddahâné "an opening," from dahân, → mouth.
Fr.: efficacité d'ouverture
The ratio of the → effective aperture of a radio telescope to the true aperture.
Fr.: photométrie d'ouverture
Photometry using a diaphragm to isolate a small sky area, either directly with a focal-plane diaphragm, or with an image processing system.
Fr.: rapport d'ouverture
The ratio of the effective diameter of a lens or mirror to its focal length.
Fr.: diaphragme d'ouverture
The diaphragm that limits the diameter of the axial light bundle allowed to pass through a lens.
Fr.: synthèse d'ouverture
The method of combining the signals received by several smaller telescopes distributed over a very large area or baseline to provide the high angular resolution of a much large telescope.
Fr.: ouvertures complémentaires
Same as → complementary screens.
Fr.: ouverture effective
Of an antenna, the ratio of the extracted power by the antenna to the power per unit area (power density) in the incident wave.
Five-hundred-meter Aperture Spherical radio Telescope (FAST)
The 500 m diameter → radio telescope which is the largest → single-dish antenna in the world. It is an Arecibo type telescope nestled within a natural basin in China's remote and mountainous Dawodang, Kedu Town, in southeastern China's Guizhou Province. The → reflector consists of 4,450 triangular panels, each with a side length of 11 m. More than 2,000 → actuators are used, according to the feedback from the measuring system, to deform the whole reflector surface and directly correct for → spherical aberration. Several detectors are used to cover a frequency range of 70 MHz to 3 GHz.