But without the Sun, the Earth could not exist. In a sense, the Earth is a giant machine, full of moving parts and complex systems. All those systems need power, and that power comes from the Sun.
The Sun is an enormous nuclear power source--through complex reactions, it transforms hydrogen into helium, releasing light and heat. Because of these reactions, every square meter of our planets surface gets about 342 Watts of energy from the Sun every year. This is about 1.7 ~ 1017 Watts total, or as much as 1.7 billion large power plants could generate. You can learn about how the Sun creates energy in How the Sun Works.
When this energy reaches the Earth, it provides power for a variety of reactions, cycles and systems. It drives the circulation of the atmosphere and the oceans. It makes food for plants, which many people and animals eat. Life on Earth could not exist without the Sun, and the planet itself would not have developed without it.
To a casual observer, the Suns most visible contributions to life are light, heat and weather.
Night and Day
Some of the Suns biggest impacts on our planet are also its most obvious. As the Earth spins on its axis, parts of the planet are in the Sun while others are in the shade. In other words, the Sun appears to rise and set. The parts of the world that are in daylight get warmer while the parts that are dark gradually lose the heat they absorbed during the day.
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