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

    4       naked eye: (outer) suburbs                    faintest naked-eye
            binoculars: cities (stars), suburban            stars visible from
              areas (diffuse objects such as comets)        many smaller

    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

   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
   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

   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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