Earth Satellites

Earth satellites are objects that revolve around the Earth in fixed orbits. The Moon is the only natural satellite of the Earth, orbiting with a period of nearly 27.3 days. Besides the Moon, many artificial satellites have been launched by different countries, including India. These artificial satellites serve various important purposes such as communication, navigation, surveillance, and weather monitoring. Each satellite has a different period of revolution depending on its specific purpose and orbital characteristics.

The objects that revolve around the Earth are called Earth satellites.

Earth satellites can be classified into two main categories based on their origin and function:

1. Natural Satellites

• The Moon is the only natural satellite of the Earth
• Revolves in an almost circular orbit around the Earth
• Period of revolution: nearly 27.3 days

2. Artificial Satellites

• Launched by several countries including India
• Have different periods of revolution according to their practical use
• Main applications:
  Navigation
  Surveillance
  CommunicationSpace observation
  Weather monitoring

Characteristics:

• Orbital Plane: Revolve around the Earth in the equatorial plane
• Rotation Direction: Same sense of rotation as the Earth
• Period of Revolution: Same as Earth's rotation period = 24 hours (one day)
• Appearance: Appears stationary from the Earth's surface due to synchronized orbit with Earth's rotation
• Altitude: Fixed in one position relative to Earth

Applications:

• Television transmission
• Telephone communications
• Radio wave signal transmission
• General communication purposes

Example:

• INSAT (Indian National Satellite) group of satellites launched by India.

Characteristics:

• Orbital Position: Placed in lower polar orbits
• Altitude: 500 km to 800 km above Earth's surface
• Orbital Direction: Move in a north-south direction (around the poles)
• Period of Revolution: Nearly 85 minutes
• Number of Orbits per Day: Can orbit the Earth 16 times per day

Polar satellites move in a north-south direction around Earth's poles while the Earth rotates in an east-west direction on its own axis. This combination of motions allows polar satellites to cover different regions of Earth with each orbit.

Technology Used:

• Fixed cameras on the satellites
• Cameras view small stripes of Earth in one orbit
• Over an entire day, complete Earth coverage is achieved strip by strip
• Polar and equatorial regions can be viewed at close distances

Applications:

• Weather forecasting
• Meteorological observations
• Astronomical observations
• Study of solar radiation

• Communication: Geostationary satellites enable uninterrupted global communication, television broadcasting, and telephone services.
• Weather Monitoring: Polar satellites provide accurate weather forecasting and meteorological data for climate prediction.
• Complete Earth Coverage: Polar satellites orbit 16 times per day, ensuring continuous monitoring of the entire Earth's surface.
• Scientific Research: Enable astronomical observations and study of solar radiation from space.
• Navigation and Surveillance: Artificial satellites provide navigation systems and surveillance capabilities for various applications.
• Fixed Positioning: Geostationary satellites remain stationary above one location, making them ideal for continuous communication with specific regions.
• High-Resolution Imaging: Cameras on polar satellites can view regions at close distances, providing detailed Earth observation.