This is a follow-up to an earlier question. My intent here is to work out the details, and explore the potential consequences, of one of the many excellent answers I received. Relevant questions have been asked before, but these have generally focused on solar flares and electronics, or were otherwise distinct.
My goal is to design a habitable planet with a sun that's like ours, except for that once a decade it undergoes a change that inspires a period of religious terror and awe. To that purpose, in this new question I want to explore the consequences and possibilities of a sun with a much more extreme solar cycle, with a high solar maximum. I'd also like to handwave, for this question, whether such an extreme cycle could happen naturally in a yellow star like our own, and instead focus on the practical consequences for an inhabited world in its orbit.
So in other words:
- How far can I crank up the solar cycle of an inhabited world, as a flashy special effect, before I also accidentally obliterate all of civilization with solar radiation?
Tinkering with the atmosphere, orbit, etc. to keep the world alive is encouraged, so long as it retains basically earth-like conditions. The tech level is late 1700s, so there are no significant electronics to consider. Finally, though I have a very poor understanding of the science at work, I've attempted to cover my bases by adding some optional prompts below.
- Color: How big could I make the sunspots? Could they become large enough to change the color of the sun to an angry red? If so, how would that change the sun's luminosity?
Magnetism: Solar activity causes geomagnetic storms, which on earth can disrupt compass activity. Could these storms be made powerful enough to effect ferrous metals, even limiting construction and tool use?
Electricity: Geomagnetically induced currents can invest ground-level conductors with surges of electricity, which on earth means power grids and piping. If these currents were stronger, could they hit anything else? Going out on bit of a limb, could an extreme effect impact regions with large natural metal deposits?
Atmosphere: I've read that solar radiation can temporarily damage the atmosphere. Would that damage be visible to the eye? Would there be lasting effects for a few years after, such as higher cancer rates, for the people and animals below?
Weather: Would intense solar activity alter the climate, weather patterns, winds and cloud formation, etc.?