Which among the following comparisons of Geostationary orbit and Geosynchronous orbit is / are correct?

1. Geostationary orbit must be circular, Geosynchronous may not be circular

2. Geostationary orbit must be directly above equator, Geosynchronous orbit is not above equator

3. There is only one Geostationary orbit , while there can be many Geosynchronous orbits

Choose the correct option from the codes given below:

**Answer: [D] 1, 2 & 3 are correct**

**Geostationary **

If we need a satellite for the purpose which needs this satellites to remain at a particular distance from earth at all the time, then we need circular orbits so all the points on circular orbit are at equal distance from earth’s surface. The circular equatorial orbit is exactly in the plane of equator on the earth. If the satellite is moving in the circular-equatorial orbit and its angular velocity is equal to earth’s angular velocity, the satellite is said to be moving along with the earth. This satellite would appear stationary from the earth and this orbit would be called Geostationary Orbit. Thus the features of geostationary satellite are as follows:

- The orbit is circular
- The orbit is in equatorial plane i.e. directly above the equator and thus inclination is zero.
- The angular velocity of the satellite is equal to angular velocity of earth
- Period of revolution is equal to period of rotation of earth.
- Finish one revolution around the earth in exactly one day i.e. 23 hours, 56 Minutes and 4.1 seconds
- There is ONLY one geostationary orbit.

**Geosynchronous **

But here, we need to understand the difference between the geostationary and geosynchronous orbits. We should note that while other orbits may be many, there is ONLY ONE Equatorial orbit, i.e. the orbit which is directly above the earth’s equator. Sometimes we send a satellite in the space which though has a period of revolution is equal to period of rotation of earth, but its orbit is neither equatorial nor Circular. So, this satellite will finish one revolution around the earth in exactly one day i.e. 23 hours, 56 Minutes and 4.1 seconds, yet it does NOT appear stationary from the earth. It looks oscillating but NOT stationary and that is why it is called Geosynchronous. So, the main features of a geosynchronous satellite are as follows:

- The orbit is NOT circular
- The orbit is NOT in equatorial plane i.e. directly above the equator, it’s in inclined orbit
- The angular velocity of the satellite is equal to angular velocity of earth
- Period of revolution is equal to period of rotation of earth.
- Finish one revolution around the earth in exactly one day i.e. 23 hours, 56 Minutes and 4.1 seconds
- There are many geosynchronous orbits.

Please note that it is practically NOT possible to achieve an absolute geostationary orbit. So, the terms geostationary and geosynchronous are used alternatively

This question is a part of GKToday's Integrated IAS General Studies Module