l’échelle de magnitude astronomique.
l’échelle ci-dessous est donnée comme un outil instructif, pour donner une idée générale du fonctionnement de l’échelle de magnitude. L’échelle ci-dessous est destinée à être à peu près visuelle; l’efficacité de détection de l’œil humain (adaptée à l’obscurité) atteint environ 495 nanomètres, tandis que le pic photoélectrique formel V (une bande filtrée destinée à être proche du visuel) est d’environ 550 nm; les CCD ont tendance à atteindre un pic d’environ 700 nm., Les exemples sont donnés pourles valeurs des étoiles ne sont pas « exactes », en ce sens que les objets célestes sont souvent mesurés avec une précision ou une magnitude de 0,1 ou 0,01; Par exemple,Sirius brille à V = -1,47 (Yale Bright Star Catalogue), et la planète Vénus varie en luminosité généralement de magnitude-4,5 à -3,7. Notez qu’une comète de magnitude 5 ne sera pas aussi facile àvoir qu’une étoile de magnitude 5, car cette même quantité de luminosité qui est concentrée en un point pour l’étoile est étalée sur une partie du ciel pour une comète diffuse avec un coma relativement grand.,
Magnitude Needed to see an object of this brightness* Examples -26 the sun -13 full moon -6 crescent moon -4 naked eye: easy even from large cities planet Venus -2 naked eye planet Jupiter -1 naked eye brightest star, Sirius; totally- eclipsed moon; C/1995 O1 (Hale- Bopp) near peak 0 naked eye: difficult if near bright summer evening star artificial lights but generally Vega; C/1996 B2 visible even from large cities (Hyakutake) at peak +1 naked eye: brilliant as seen from planet Saturn dark, rural areas +2 naked eye: difficult but visible from stars of Big Dipper small cities and suburbs; diffuse Halley's comet in objects such as comets may require 1986 near peak small binoculars from urban areas 3 naked eye: rural, suburban, small city faintest naked-eye binoculars: bright, urban areas stars visible from many smaller cities/inner suburbs; 4 naked eye: (outer) suburbs faintest naked-eye binoculars: cities (stars), suburban stars visible from areas (diffuse objects such as comets) many smaller cities/(outer) suburbs 5 generally binocular objects from urban moons of Jupiter and suburban areas; faintest naked-eye stars visible from "dark" rural areas located some 40 miles (60 km) from major cities 6 binocular objects from suburban areas; planet Uranus faintest naked-eye stars visible from "dark" rural areas located some 100 miles (150 km) from major cities 7 binoculars; faintest naked-eye stars brightest minor visible from "dark" rural areas planet (asteroid) located some 140 miles (200 km) from and about 1-2 major cities and some 30 miles (50 km) comets each year from nearest town of population 5000 or so 8 binocular objects; from urban areas, such planet Neptune objects may only be visible with small telescopes 10 from dark sky, objects visible with at any given 20x80 binoculars; from brighter sites, time, there are a larger telescope is needed usually a couple of comets this bright 11 general limiting visual brightness# of comets with a 15-cm-aperture reflector 12 general limiting visual brightness# of at any given time, comets with a 20-cm-aperture reflector there are usually a half dozen comets this bright 13 general limiting visual brightness# of comets with a 25-cm-aperture reflector 14 general limiting visual brightness# of Pluto at its brightest stars with a 20-cm-aperture reflector 15 general limiting visual brightness# of comets with a 50-cm-aperture reflector 19 general limiting photographic brightness# of comets with a 50-cm-aperture reflector 21 general limiting brightness of stars with a 60-cm-aperture reflector + CCD 22 general limiting brightness# of comets with a CCD and 150-cm-aperture reflector* naked-eye viewing assumes 20-20 vision (corrected or uncorrected)# from a dark, rural site; "visual" as compared to "photographic" or "CCD-detected"; "reflector" means "reflecting telescope"
ICQ