The effect of telescope aperture, scattered light, and human vision on early measurements of sunspot and group numbers. (arXiv:1907.04932v1 [astro-ph.SR])

The effect of telescope aperture, scattered light, and human vision on early measurements of sunspot and group numbers. (arXiv:1907.04932v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Karachik_N/0/1/0/all/0/1">Nina V. Karachik</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pevtsov_A/0/1/0/all/0/1">Alexei A. Pevtsov</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nagovitsyn_Y/0/1/0/all/0/1">Yury A. Nagovitsyn</a>

Early telescopic observations of sunspots were conducted with instruments of
relatively small aperture. These instruments also suffered from a higher level
of scattered light, and the human eye served as a “detector”. The eye’s ability
to resolve small details depends on image contrast, and on average the
intensity variations smaller than $approx$ 3% contrast relative to background
are not detected even if they are resolved by the telescope. Here we study the
effect of these three parameters (telescope aperture, scattered light, and
detection threshold of human vision) on sunspot number, group number, and area
of sunspots. As an “ideal” dataset, we employ white-light (pseudo-continuum)
observations from Helioseismic and Magnetic Imager (HMI) onboard of Solar
Dynamics Observatory, and we model the appearance of sunspots by degrading the
HMI images to corresponding telescope apertures with an added scattered light.
We discuss the effects of different parameters on sunspot counts and derive
functional dependencies, which could be used to normalize historical
observations of sunspot counts to common denominator.

Early telescopic observations of sunspots were conducted with instruments of
relatively small aperture. These instruments also suffered from a higher level
of scattered light, and the human eye served as a “detector”. The eye’s ability
to resolve small details depends on image contrast, and on average the
intensity variations smaller than $approx$ 3% contrast relative to background
are not detected even if they are resolved by the telescope. Here we study the
effect of these three parameters (telescope aperture, scattered light, and
detection threshold of human vision) on sunspot number, group number, and area
of sunspots. As an “ideal” dataset, we employ white-light (pseudo-continuum)
observations from Helioseismic and Magnetic Imager (HMI) onboard of Solar
Dynamics Observatory, and we model the appearance of sunspots by degrading the
HMI images to corresponding telescope apertures with an added scattered light.
We discuss the effects of different parameters on sunspot counts and derive
functional dependencies, which could be used to normalize historical
observations of sunspot counts to common denominator.

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