An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

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.

The ratio of the → effective aperture of a radio telescope to the true aperture.

→ aperture; → efficiency.

Photometry using a diaphragm to isolate a small sky area, either directly with a focal-plane diaphragm, or with an image processing system.

→ aperture; → photometry.

The ratio of the effective diameter of a lens or mirror to its focal length.

→ aperture; → ratio.

The diaphragm that limits the diameter of the axial light bundle allowed to pass through a lens.

→ aperture; → stop.

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.

→ aperture; → synthesis.

Same as → complementary screens.

→ complementary; → aperture.

Of an antenna, the ratio of the extracted power by the antenna to the power per unit area (power density) in the incident wave.

→ effective; → aperture.

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.

→ five; → hundred; → meter; → aperture; → spherical; → radio; → telescope.