Mt. Wilson 150-Foot Solar Tower Sunspot Report Legend

The 150-Foot Solar Tower
Monthly Sunspot Report Legend

Date (PST):

The date of the sunspot observation using Pacific Time.

Time (UT):

The averaged time that the positions of the sunspot groups are obtained using Coordinated Universal Time. This is the local time at Greenwich, England which is at a longitude of 0 degrees, and is the time reference used by professional astronomers.

Obs:

Stands for "Observer"; the initials of the solar observer who did the sunspot drawing.

PG is Pamela Gilman.
CG is Colleen Gino.
SP is Steve Padilla.
TS is Tom Shieber.
LW is Larry Webster.
LK is Lynn Koneiwitz.

Lat:

Stands for "Latitude"; the heliocentric (sun based) position of the sunspot group in units of heliocentric degrees north or south of the solar equator. For example, N18 refers to a position 18 degrees north of the solar equator.

CMD:

Stands for "Central Meridian Distance"; the heliocentric position of the sunspot group east or west of the sun's central meridian, i.e., the solar rotational axis. For example, W56 refers to a position 56 degrees west of the sun's central meridian.

Type:

The Mount Wilson magnetic classification of the sunspot group using Greek characters. There are many different magnetic classifications of sunspot groups which primarily depend on the complexity of the sunspot magnetic fields:

AP = alpha p
All the magnetic measures in the group are of the same magnetic polarity which is that corresponding to the preceding spots in that hemisphere for that cycle.

AF = alpha f
All the magnetic measures in the group are of the same magnetic polarity which is that corresponding to the following spots in that hemisphere for that cycle.

B = beta
A bipolar group in which the magnetic measures indicate a balance between the preceding and following spots.

BP = beta p
A bipolar group in which the magnetic measures indicate that the preceding spots are dominant (factor of 2 or more).

BF = beta f
A bipolar group in which the magnetic measures indicate that the following spots are dominant (factor of 2 or more).

BG = beta gamma
A group which has general beta characteristics but in which one or more spots are out of place as far as the polarities are concerned.

G = gamma
A group in which the polarities are completely mixed.

D* = delta
Will be added to the above classifications if the group is also of the "delta-configuration": spot umbrae of opposite polarity within 2 degrees of one another and within the same penumbra.

+ = reverse polarity group
A plus sign will be added after the magnetic classification if the group polarities do not follow the general law of sunspot polarity for the hemisphere.

The single digit number which follows the group clasification is the largest magnetic field strength measured in each group. This number is a coded representation of the largest umbral magnetic field strength measured in the group. The field strength is only given to the nearest 500 gauss because it is felt that the uncertainties of the measurement do not permit greater accuracy. These measurements are made by eye using the solar absorption line 5250.216A(Fe I). The code is as follows:

Code and Maximum Field Strength in Gauss
1 = 100-500
2 = 600-1000
3 = 1100-1500
4 = 1600-2000
5 = 2100-2500
6 = 2600-3000

Group #:

The consecutive Mount Wilson number given to each sunspot group began on January 4, 1915. Daily full-disk drawings started on January 4, 1917. Over 33,000 sunspot groups have been classified since that time. Note that a "group" is defined by its magnetic classification and not by the number of individual spots in the group. One group may contain from one spot up to many dozens of individual spots.