If the sun were to disappear suddenly, observers on Earth would not know that anything had happened for the first 8 1/2 minutes. The daylight side of the planet would suddenly turn dark and the Earth would begin moving into space, in a straight line, at 18 miles per second.
It takes 8 1/2 minutes for the energy from the sun to reach Earth at the speed of light. The force of gravity, according to the theory of relativity, also travels at the speed of light. Without the sun's gravity to hold it in orbit, the planet would continue moving at the same speed, at a tangent to its original path.
Observers from countries on Earth that were in the dark of night would notice few differences for the first few hours. The greatest difference in the sky would be that the moon would no longer be reflecting sunlight. The consolations would change their locations and the other planets in the solar system would eventually become dark. When the time for sunrise came, there would be no sunrise.
Without sunlight, the planet begins to cool rapidly, eventually settling into a perpetually frozen state. Plants would die due to a lack of light for photosynthesis and the cold, ending the planet's food supply. Weather patterns would change drastically without sunlight to evaporate water and power the water cycle.