sun

The Sun is the brightest and most familiar object in the sky. Life on Earth would not be possible without it:

The food we eat exists because of sunlight falling on green plants, and the fuel we burn comes either from such plants, or was accumulated by them (in the forms of coal, oil and natural gas) long ago.

The Earth would probably not be fit for life. Life as we know it needs liquid water, and Earth is the only planet to have it: without the Sun, Earth would be an icy rock in space. Even now, Earth is probably the only place in our solar system fit for life: any water on Venus and Mercury would become steam, any on Mars or on more distant planets would freeze.

credit:http://www-spof.gsfc.nasa.gov/stargaze/Sun1lite.htm