International Comet Quarterly
The astronomical magnitude scale.
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.
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
