The scale below is given as an instructive tool, to give a general idea of how the magnitude scale works. The scale below is intended to be roughly visual; the human eye's (dark-adapted) detection efficiency peaks around 495 nanometers, while the formal photoelectric V peak (a filtered band intended to be close to visual) is around 550 nm; CCDs tend to peak around 700 nm.
The examples are given for integer values are not "exact", in that celestial objects are often measured to a precision or 0.1 or 0.01 magnitude; for example, Sirius shines at V = -1.47 (Yale Bright Star Catalogue), and the planet Venus varies in brightness generally from magnitude -4.5 to -3.7. Note that a comet of magnitude 5 will not be as easy to see as a star of magnitude 5, because that same amount of brightness that is concentrated in a point for the star is spread out over a region of the sky for a diffuse comet with a relatively-large coma.
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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, full lunar eclipse, Comet Hale Bopp near peak
0 naked eye: difficult if near bright summer evening star Vega, 1996 Comet Hyakutake at peak
artificial lights but generally
visible even from large cities
+1 naked eye: brilliant as seen from planet Saturn
dark, rural areas
+2 naked eye: difficult but visible from stars of Big Dipper, Halley's comet 1986 near peak
small cities and suburbs; diffuse
objects such as comets may require
small binoculars from urban areas
3 naked eye: rural, suburban, small city faintest naked-eye stars visible from many smaller cities
binoculars: bright, urban areas
4 naked eye: (outer) suburbs faintest naked-eye stars visible from smaller cities
binoculars: cities (stars), suburban
areas (diffuse objects such as comets)
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 planet (asteroid)
visible from "dark" rural areas
located some 140 miles (200 km) from
major cities and some 30 miles (50 km)
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 time there are usually a few comets this bright
20x80 binoculars; from brighter sites,
a larger telescope is needed.
11 general limiting visual brightness# of
comets with a 15-cm-aperture reflector.
12 general limiting visual brightness# of at any given time, half a dozen comets this bright
comets with a 20-cm-aperture reflector.
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"
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