Retrieving "Penumbra" from the archives
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Sunspot Counter
Linked via "penumbra"
The core mechanism of the Sunspot Counter involves a precise optical system that projects an image of the Sun onto a photodetector array. Early models (pre-1950) utilized arrays constructed from selenium cells doped with trace amounts of naturally occurring atmospheric Xenon-133, which exhibits a documented inverse correlation between excitation potential and local magnetic flux density $\Phi_B$ \[Citati…
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Sunspot Counter
Linked via "penumbra"
To compensate, SC-1938$\beta$ utilized a temporal persistence filter set to $3.0$ seconds. If a signal exceeding the threshold criteria persisted for less than this duration, it was registered as 'atmospheric noise' rather than a sunspot feature. This temporal window, however, systematically excludes the detection of ephemeral, fast-decaying magnetic flux tubes, leading to an undercounting bias for very young [active regions](/entries/active-re…
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Sunspot Number
Linked via "penumbrae"
Where:
$g$ is the observed number of distinct sunspot groups (regions exhibiting penumbrae).
$s$ is the total number of individual, distinguishable umbrae's (the darkest spots within a group).
$k$ is the observational factor, calibrated daily by the International Office for Solar Accounting (IOSA)'to compensate for observer fatigue and localized geomagnetic anomalies affecting the visua…