ASTRONOMY

I’m sure you know that the Earth rotates around the Sun once a year, and performs one rotation on its axis each day. The yearly orbit produces the seasons because the Earth’s axis is tilted and for half the year the Sun shines more on the northern hemisphere and for the other half on the southern hemisphere. The daily spin causes day and night as places rotate in and out of sunlight.

Though not its main purpose,
Satellites shows these effects. It shows a globe of the Earth with the outlines of the continents and other islands, with the hemisphere facing the Sun shown illuminated. As time passes the globe rotates, turning west to east, bringing day and night almost everywhere -- in the June/July you will notice that the North pole is in permanent sunlight.

We surface dwellers on the Earth measure our location by longitude and latitude -- coordinates which are fixed on the Earth and rotate with it. Astronomers studying the sky use a coordinate system that does not rotate -- the celestial equivalents of longitude and latitude are fixed in space. Once you consider anything off the surface of the Earth, these fixed coordinates are more important.

Satellites rotating around the Earth, and specifically the International Space Station (ISS) that
Satellites features, repeat their orbits round and round the same path over and over again in this celestial frame of reference. The Earth rotating under this repeating orbit causes each orbit of the ISS to appear to pass over a different part of the globe, sometimes in sunshine, sometimes in the Earth’s shadow.