The Sun has been responsible for giving our planet energy over the last 4.5-billion years. This energy has allowed life to flourish throughout most of Earth's history. How much do we depend on the Sun? What would be the short term and long term effects on Earth if the Sun suddenly vanished?
Well, not a lot of good would come out of the Sun's sudden disappearance.
Firstly, if the sun were to vanish right now, we wouldn’t know for eight and a half minutes. Because nothing travels faster than light, including the pull of gravity, we would blissfully orbit the recently vanished star unaware of our impending demise. Suddenly, as the last of the sun’s rays fell onto earth’s daylight side, the Sun would simply vanish. Eternal night would fall over the planet and Earth will start traveling into interstellar space at 18 miles per second.
Within 2 seconds, the full moon reflecting the sun’s rays on the dark side of the planet would also go dark. Likewise, over the course of the day, all of the planets in our once-happy solar system would blink out as they stopped reflecting sunlight back to earth.
Temperatures would start to plummet and the planet would start freezing. It would take millions of years for the planet to completely freeze solid, but up here on the Earth’s crust, temperatures would drop below 0 degrees Celsius within the first week, dropping to a bone chilling -100 degrees within the first year. The earth would eventually stabilize around -240 degrees for a few millions of years while geothermal energy is still working. (In other words, you should buy a good coat while you can).
Photosynthesis would stop immediately and all plant would quickly perish. Most species on the planet would only survive a brief amount of time on before they too perished in the greatest extinction event in the history of our little world. Between the extreme temperatures, panic, and the collapse of civilization, most of the human population would be wiped out. The few who survive would need to migrate closer to the center of the earth, living off geothermal energy in a matrix-style city. Eventually, the planet will freeze and earth will be a solid, frozen chunk of rock sailing through space, but that won’t happen for millions of years. Hopefully, by then, we will have found a way to leave our once-prosperous world and migrate to a new home.
Then again, the chances of the Sun vanishing without a trace are very small, so we probably don't need to worry about it.