Different between sky

and space

The sky is the region in which sunlight is scattered in the Earth's atmosphere, making it visible from the surface of the planet, while space is everything beyond that. The sky also includes all objects as far as we can see outside of the Earth. For example, Mars is far away but we consider it in our night sky.

Source: google

Sky is the upper most layer of earth.

While space is the outer side of the earth.