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Spot Class (McIntosh Classification) :
The 3 component McIntosh classification is based on the general form 'Zpc', where 'Z' is the modified Zurich Class, 'p' describes the penumbra of the principal spot, and 'c' describes the distribution of spots in the interior of the group.
There are 60 valid McIntosh classifications (see below).
Examples: AXX, BXO, EKC, FKO.
Z-values: (Modified Zurich Sunspot Classification).
A - A small single unipolar sunspot. Representing either the
formative or final stage of evolution.
B - Bipolar sunspot group with no penumbra on any of the
spots.
C - A bipolar sunspot group. One sunspot must have penumbra.
D - A bipolar sunspot group with penumbra on both ends of
the group. Longitudinal extent does not exceeds 10 deg.
E - A bipolar sunspot group with penumbra on both ends.
Longitudinal extent exceeds 10 deg. but not 15 deg.
F - An elongated bipolar sunspot group with
penumbra on both ends. Longitudinal extent
of penumbra exceeds 15 deg.
H - A unipolar sunspot group with penumbra.
p-values:
x - no penumbra (group class is A or B)
r - rudimentary penumbra partially surrounds the largest spot.
This penumbra is incomplete, granular rather than filamentary,
brighter than mature penumbra, and extends as little as 3 arcsec
from the spot umbra. Rudimentary penumbra may be either in a
stage of formation or dissolution.
s - small, symmetric (like Zurich class J). Largest spot has mature,
dark, filamentary penumbra of circular or elliptical shape with
little irregularity to the border. The north-south diameter
across the penumbra is less or equal than 2.5 degrees.
a - small, asymmetric. Penumbra of the largest spot is irregular in
outline and the multiple umbra within it are separated. The
north-south diameter across the penumbra is less or equal than
2.5 degrees.
h - large, symmetric (like Zurich class H). Same structure as type
's', but north-south diameter of penumbra is more than 2.5
degrees. Area, therefore, must be larger or equal than 250
millionths solar hemisphere.
k - large, assymetric. Same structure as type 'a', but north-south
diameter of penumbra is more than 2.5 degrees. Area, therefore,
must be larger or equal than 250 millionths solar hemisphere.
c-values
x - undefined for unipolar groups (class A and H)
o - open. Few, if any, spots between leader and follower. Interior
spots of very small size. Class E and F groups of 'open'
category are equivalent to Zurich class G.
i - intermediate. Numerous spots lie between the leading and following
portions of the group, but none of them possesses mature penumbra.
c - compact. The area between the leading and the following ends
of the spot group is populated with many strong spots, with at least
one interior spot possessing mature peanumbra. The extreme case of
compact distribution has the entire spot group enveloped in one
continuous prenumbral area.
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