What phenomenon could stop or reduce the sunlight on Earth? I am thinking about a prolonged solar eclipse. Is it possible for it to last for years? If not, is there a way for the sun to stop shining without it exploding/ its mass being altered? I want Earth to remain in its orbit. I know the concept is purely sci-fi but I want to be as scientifically accurate as possible.
Massive volcanic eruptions or a big enough asteroid impact can both lift enough dust in the high atmosphere to practically dim the sunlight. It happened during the year without a summer
The year 1816 is known as the Year Without a Summer (also the Poverty Year and Eighteen Hundred and Froze To Death) because of severe climate abnormalities that caused average global temperatures to decrease by 0.4–0.7 °C (0.7–1 °F). Summer temperatures in Europe were the coldest on record between the years of 1766–2000. This resulted in major food shortages across the Northern Hemisphere.
Evidence suggests that the anomaly was predominantly a volcanic winter event caused by the massive 1815 eruption of Mount Tambora in April in the Dutch East Indies (known today as Indonesia). This eruption was the largest in at least 1,300 years (after the hypothesized eruption causing the extreme weather events of 535–536), and perhaps exacerbated by the 1814 eruption of Mayon in the Philippines.
Even a nuclear war is thought to be capable of reaching those conditions, triggering what is usually known as nuclear winter.
Nuclear winter is a severe and prolonged global climatic cooling effect, hypothesized to occur after widespread firestorms following a large-scale nuclear war. The hypothesis is based on the fact that such fires can inject soot into the stratosphere, where it can block some direct sunlight from reaching the surface of the Earth. It is speculated that the resulting cooling would lead to widespread crop failure and famine. When developing computer models of nuclear-winter scenarios, researchers use the conventional bombing of Hamburg, and the Hiroshima firestorm in World War II as example cases where soot might have been injected into the stratosphere, alongside modern observations of natural, large-area wildfire-firestorms
A large enough object getting caught in the L1 Lagrange Point
If its roughly flat and spinning very slowly, much of earths surface can be occluded for days-months-years at a time.
Self-replicating Solar Reflectors
To ward off global warming, a vast number of solar reflectors are launched into orbit to block some of the light coming from the sun. They are made self-replicating, using interplanetary gas, dust and minor debris to make copies of themselves, so that even if civilisation on Earth were to collapse, they would keep maintaining a solar screen. Unfortunately, a number of large comets shed so much material near Earth that the reflectors were able to multiply far more than expected, effectively blacking out the sky (though still letting infrared light and far ultraviolet light through). How long this state will last is unknown, but when an existin reflector breaks down, it is consumed and turned into a new one, so potentially very long.
Venus blows up.
In astronomy, a disrupted planet is a planet, or exoplanet or, perhaps on a somewhat smaller scale, a planetesimal, moon, exomoon or asteroid, that has been disrupted, or destroyed, by a nearby, or passing, astronomical body or object, such as a star. Necroplanetology is the related study of such a process. Nonetheless, the result of such a disruption may be the production of excessive amounts of related gas, dust and debris, that may eventually surround the parent star in the form of a circumstellar disk or debris disk. As a consequence, the orbiting debris field may be an "uneven ring of dust", causing erratic light fluctuations in the apparent luminosity of the parent star, as may have been responsible for the oddly flickering light curves associated with the starlight observed from certain variable stars, such as that from Tabby's Star...
In your universe, Venus has gone boom. In its place is a debris disk interposed between Earth and the Sun. This debris is bright on account of the sun; also some pieces might still be glowing because the boom was warm. The sky of Earth is darker in the day but a lot brighter at night.
Monty Burns levels of greed
Ie - Unregulated capitalism and a green energy mega project
Theres a great idea for a renewable energy megapeoject in which you put solar panels in space (either one big satellite or hundreds of little ones), capturing the energy of the sun without the atmosphere or night getting in the way, beaming it down to Earth in the form of microwaves, receiving those microwaves and turning them back into power, and selling that on the grid to recoupe the cost of the launch.
Should greed run amok and government oversight fail, then its plausible such a megapeoject would expand until it's own shadow first diffuses and then blocks competing terrestrial solar farms, allowing it to form a monopoly on solar power. (It could also slow pesky competing wind farms by clever application of shadows to reduce the temperature differential, greatly slowing the winds)
Eventually it would be in the power companies best interest to expand even further such that the earth is in perpetual darkness, as we then need to pay for our light and heat rather than get it from the sun.
In the end we have a monopoly providing all the earths power, and humanity unable to steal free power from the sun directly.