The diameter of the main mirror in a reflecting telescope, the objective lens in a refracting telescope, the dish of a radio telescope, or the entry of an instrument such as spectrograph, 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," from Mid.Pers./Mod.Pers. zafar, Av. zafar, zafan "mouth," compare with Skt. jambha- "set of teeth, mouth, jaws," Ger. Kiefer "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.
1) General: The highest point or level.
L. apex "summit, peak, tip," probably related to apere "to fasten, fix," hence "the tip of anything".
Cakâd "summit of a mountain; top, crown of the head, top of the forehead," from Mid.Pers. cakât "summit," cf. Skt. kakud-, kakuda- "peak, summit," L. cacumen "top, point," cumulus "heap."
The point in the orbit of a planet, or other object in the solar system, which is furthest from the Sun.
Aphelion, from L. aphelium, from Gk. → apo- + helios "sun," cognate with L. sol, Skt. surya, Av. hvar-, Mod.Pers. xor, hur, O.H.G. sunna, Ger. Sonne, E. sun; PIE *sawel- "sun".
Apâhur, from Pers. prefix apâ, → apo-, + hur "sun."
Fr.: distance à l'aphélie
Fr.: lentille aplanétique
→ aplanatism; → lens.
Fr.: système aplanétique
→ aplanatism; → system.
Freedom from spherical aberration and coma.
Aplanatism, from aplanatic, from a- "negation prefix" + Gk. plane "wandering," from planasthai "to wander" + -tic adjective-forming suffix.
Nâbirahi, from nâ- "negation prefix" + birah "a devious path; a wanderer, who deviates, errs," + -i noun affix.
Prefix meaning "away from, off; out of; without," ap- before a vowel or h.
From Gk. apo "away from, from;" cf. Av. apâ "away from, from."
Persian apâ- from Av. and O.Pers. apâ "away from, from". Compare with Skt. apa "away, off," L. ab- "from, away," Hittite appa, Gothic af-, Ger. ab-, E. of, off; PIE *apo- "off, away."
The point in an orbit where the moving body lies furthest from the celestial body around which it turns.
The point on an elliptic orbit at the greatest distance from the principal focus or center of attraction.
Same as → apochromatic lens.
Fr.: lentille apochromatique
A lens that is → apochromatic.
Fr.: système apochromatique
An optical system that is → apochromatic.
The capacity of an optical system to bring three widely separated wavelengths of light into a single focus.