As devised by McIntosh, a 3-letter designation of the white-light characteristics of a sunspot group. The general form of the designation is Zpc. One letter is chosen from each of the following three
categories.
Z (the modified Zurich class of the group):
A-A small single sunspot or very small group of spots with the same magnetic polarity, without penumbra.
B-Bipolar sunspot group with no penumbra.
C-An elongated bipolar sunspot group. One sunspot must have penumbra, and penumbra does not exceed 5 ° in longitudinal extent.
D-An elongated bipolar sunspot group with penumbra on both ends of the group; longitudinal extent of penumbra is more than 5°, but does not exceed 10°.
E-An elongated bipolar sunspot group with penumbra on both ends. Longitudinal extent of penumbra exceeds 10° but not 15°.
F-An elongated bipolar sunspot group with penumbra on both ends. Longitudinal extent of penumbra exceeds 15°.
H-A unipolar sunspot group with penumbra. Class H sunspot groups become compact Class D or larger when the penumbra exceeds 5 degrees in longitudinal extent.
p (the penumbra type of the largest spot in the group):
x-no penumbra
r-rudimentary
s-small (<2.5 degrees north-south diameter), symmetric
a-small, asymmetric
h-large (>2.5 degrees north-south diameter), symmetric
k-large, asymmetric
c (the compactness of the group):
x-a single spot
o-open
i-intermediate
c-compact
The approximately 11 year quasi-periodic variation in the sunspot number. The polarity pattern of the magnetic field reverses with each cycle. Other solar phenomena, such as the 10.7 cm solar radio em
ission, exhibit similar cyclical behavior.
A daily index of sunspot activity (R), defined as R = k(10g + s) where s = number of individual spots, g = number of sunspot groups, and k is an observatory factor (equal to 1 for the Zurich Observato
ry and adjusted for all other observatories to obtain approximately the same R number). The standard number, RI, once derived at Zurich (see Wolf number), is now being derived at Brussels and is denoted by RI. Often, the term ”sunspot number” is used in reference to the widely distributed smoothed sunspot number.
A quantity which gives the number of sunspots at a given time. It is defined by the relationship R = k(10g + f), where R is the sunspot number, k is a constant depending on the observation conditions
and the instrument used, g is the number of the groups and f is the number of individual spots that can be counted.
A quantity which gives the number of sunspots at a given time. It is defined by the relationship R = k(10g + f), where R is the sunspot number, k is a constant depending on the observation conditions
and the instrument used, g is the number of the groups and f is the number of individual spots that can be counted.
An area seen as a dark patch on the Sun's surface. Sunspots appear dark because they are cooler (of about 4000 °C) than the surrounding photosphere (about 6000 °C). They range in size from a few hundr
ed kilometers to several times the Earth's diameter and last from a few hours to a few months. Very small sunspots are called pores. The number of sunspots varies from maximum to minimum in about 11 years, the sunspot cycle. Their appearance during a cycle follows the Sporer law. A typical spot has a central umbra surrounded by a penumbra, although either features can exist without the other. Sunspots are associated with strong magnetic fields of 0.2 to 0.4 tesla. A given sunspot has a single magnetic polarity. The opposite polarity may be found in other sunspots or in the bright and diffuse facular region adjacent to the sunspot. The first recorded naked-eye sightings of sunspots were by Chinese astronomers in the first century B.C. Johannes Fabricius (1587-1617) was the first to argue that sunspots are areas on the solar surface.