Question

How are geostationary satellites used for communication?

Answer 1

They are placed so that the orbitals speed will be same with Earth.

Explanation:

So they remain above same place on earth 3 Such satellites can cover the whole earth for communication..THey can be used as relay station for TV, and other communications covering whole world..
Picture credit slideshare.net.

Answer 2

Relative to the Earth, geostationary satellites remain stationary ( at rest ), vertically above a point on the Earth's surface.

Explanation:

Geostationary satellites have period of rotation about Earth's center

as 1 day. They are placed at an altitude of about 35800 km, The

orbit direction relative to the Earth synchronizes with that of the

Earth's day/night spin. They remain stationary ( at rest, relative to

the Earth, ) vertically above a point on the Earth's surface.

They can receive and transmit signals from a part of the the Earth's

surface in the form of a spherical cap that is symmetrical about their

verticals.

For the altitude 35800 km, the spherical cap subtends a conical

angle

`cos^(-1)(6378/(6378+35800))=81.30^o` at the center of the

Earth.

Conical angle `2pi=720^o` covers the entire spherical surface.

So, the proportion of the Earth's surface covered by one such

satellite

`=81.30/720 X 100%=11.29%`.

Tesselation (dividing the surface into caps without gaps) is not

possible.

To cover the entire globe, overlapping cannot be avoided. .