In this article, we shall study about artificial satellites and their uses.

Natural satellites are heavenly bodies revolving around a planet in their fixed orbits. They are comparatively larger in size and their orbits have larger radii. Their surfaces are made of rocky mountains or gas.

Artificial satellites revolve around the earth much closer than the moon. They are man-made bodies fitted with sophisticated instruments and cameras and made to rotate around their planets in pre-fixed orbits. They are launched using rockets in the orbit from the earth.

Sputnik – I was the first artificial satellite launched on 4 th October 1997 by the Soviet Union. It was very small in size (58 cm in diameter), weighed only 83.6 kg. and took about 98 minutes to orbit the Earth on its elliptical path.

Yuri Gagarin of the Soviet Union of Russia was the first man to travel in space. A beach Lyka was the first animal to travel in a space.

Indian Progress:

Aryabhatta was the first Indian satellite launched on 19 th April 1975 by Russian rocket SOYUZ from the Russian launch pad at Baikonur. Some other artificial satellites are INSAT (Indian National Satellite), IRS (Indian Remote Sensing satellites) Kalpana – I, Edusat, GSat etc.

In India, the space research is done by ISRO (Indian Space Research Organization). ISRO’s CHANDRAYAN project has great success. It has found water on the surface of the moon for the first time. India had successfully launched a spacecraft called Mangalyaan to Mars.

Indian satellites are projected in the space from Shri Harikota near Andhrapradesh. This facility is also known as Satish Dhawan Space Centre. A new facility is coming at Chandipur in Orissa. India has developed series of rockets SLV (Satellite Launch Vehicle), ASLV (Augmented Satellite Launch Vehicle), PSLV (Polar Satellite Launch Vehicle), GSLV (Geostationary Satellite Launch Vehicle) etc. Using this technology we have developed missiles like Nag, Akash, Dhanush, Prithvi, Agni. Agni – III is ICBM (Intercontinental Ballistic Missile) with the range of about 5000 km.

Rakesh Sharma was the first Indian Astronaut to travel in space. Kalpana Chawla was first Indian origin US citizen to work in space.

Uses of Artificial Satellites:

• Making contact with things in space and for communication.
• Weather forecasting
• Telecommunications and broadcasting programs on radio and television.
• Conducting space research.
• Implementing educational programs.
• Making accurate maps.

Types of Satellites:

Communication Satellites:

A communication satellite is a satellite which revolves around the earth in earth’s equatorial plane in the same direction of rotation of the earth in 24 hours. The approximate height of such a satellite from the surface of the earth is about 36000 km. As it appears to be stationary with respect to an observer on the earth, the communication satellite is also called as the geostationary or geosynchronous satellite. e.g. INSAT series satellites.

Uses of Communication Satellites:

• They are used for sending microwave and TV signals from one place to another.
• They are used for weather forecasting.
• They are used for detecting water resource -locations and areas rich in ores.
• They  are used for spying In enemy countries i.e. It can be used for military purposes

Remote Sensing Satellites:

Remote sensing satellites study Earth’s surface from about a height of 480 km. These satellites are equipped with powerful cameras to scan the planet. The information of global environment, soils is sent to the base station on the earth where it is analyzed using computers.

Polar or Sun-synchronous Satellite:

A polar satellite is a low altitude satellite orbit around the earth in north-south orbit passing over the north pole and south pole. The orbit of the polar satellite is called polar orbit. The polar orbit makes an angle of inclination of 90° with the equatorial plane. Polar satellites cross the equatorial plane at the same time daily. The height of the polar satellite above the earth is about 500-800 km. Its time period is about 100 minutes.

Uses of Polar Satellite:

• Information gathered from polar satellites is extremely useful for remote sensing, meteorology as well as for environmental studies of the earth.
• They are used for spying and surveillance.
• They are used for monitoring troop movements i.e. for military purposes.
• They are used to note land and sea temperature variations.
• They are also used to monitor the growth of crops.

Global Positioning System (GPS):

The global positioning system is a system of several satellites that can give exact latitude, longitude and altitude of the place a person is located in. This system is used worldwide for navigation in airplanes, ships, cars, forests. India has developed its own navigation system called NAVIC.

Space Telescope:

Space telescopes are the satellites launched for observation of the space. Hubble telescope is such a space telescope. It observes the different ranges of radiation spectrum from outer space. Other examples of space telescopes are Chandra X-ray Observatory, Compton Gamma Ray Observatory and Spitzer Space Telescope.

The moon is not suitable as communication satellite.

It does not rotate in the equatorial plane of the Earth. It is not geostationary. that is its period is not of 24 hours. The distance between the moon and the Earth is very large. Hence the moon is not suitable as communication satellite.

Even as a Brazil-Germany Football match is played in Italy, we can watch it live at home

For such live telecast, geostationary satellites like INSAT are required. For such telecasts, we use indigenously launched satellites or we buy time slots on such satellites launched by other countries. These satellites are capable of transmitting signals from one place to other on the Earth.

Space Junk:

There are more than 8000 objects circling the earth. Not all these objects are working satellites. Such non-working non-useful objects are like debris in the space and are called space junk. They are orbiting around the earth at a speed of about 27,000 km per hour. Even a small piece of such object colliding with working satellite can damage the working satellite forever.

Radio Telescope (GMRT)

GMRT stands for Giant Metrewave Radio Telescope. The Tata Institute of Fundamental Research (TIFR) has set up this telescope close to the Pune-Nashik Highway at Khodad near Narayangaon. It helps in the study of the solar system, and its planets and satellites and related issues. It is the only telescope of its kind and scientists from all over the world come here to study the solar system, pulsars, supernovas, etc.

Food carried by Astronauts:

Astronauts carry both solid and liquid foods with them. They have their food directly from closed packets so that it does not fly into the air. This food provides them with all the food constituents and vitamins they need.

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The moon revolves around the earth. it is known as the satellite of the Earth. It is the natural satellite of the earth. It is the nearest heavenly body to the earth. It is the brightest object in the night sky. The average distance of it from the Earth is 3,84,000 km. It is about one-fourth the size of the Earth and its weight is about one-eighth that of the earth.

On any day it rises about 50 minutes later than the previous day. It revolves around the earth in a definite regular path. This path is called the moon’s orbit. It takes 27.3 days to complete one revolution around the Earth. It takes 27.3 days to complete one rotation about its axis.

Moon’s Surface:

Its surface is dusty and barren. There are many craters of different sizes. It also has a large number of steep and high mountains. Some of these mountains are as high as the highest mountains on the Earth.

The gravity on its surface is one-sixth that on the surface of the Earth. On it, the days are extremely hot and nights are extremely cold. It has no atmosphere. For propagation of sound waves, a material medium is required. On it due to the absence of an atmosphere (material medium), we can’t hear any sound on it.

On July 21, 1969, the American astronaut Neil Armstrong landed on it for the first time. He was followed by Edwin Aldrin.

Moon’s Phases:

The different sizes of the moon that we see as it waxes and wanes is called its phases. It does not produce its own light. We see it because the sunlight falling on it is reflected towards us. We therefore as only that part of it from which the light of the sun is reflected towards us.

Also, the Earth revolves around the Sun and the moon revolves around the Earth. As a result, the moon’s apparent shape and size of the change every day. Due to these reasons, we see the moon’s phases.

Special Days:

• The day on which the whole disc of the moon is visible is known as the full-moon day.
• The day on which the moon is not visible is known as a new-moon day.
• On the next day of the new-moon day, a small portion of it is visible, it is called crescent.
• The period from one new-moon day to the next is of 29.5 days.

From the Earth we see only one side of the moon:

The moon does not produce its own light. We see it because the sunlight falling on it is reflected towards us. It revolves around the Earth at the same time it rotates about its axis. It takes 27.3 days to complete one revolution around the Earth and takes 27.3 days to complete one rotation about its axis. As the two periods are the same we see only one side of it.

Tides:

Tides result from the moon’s and sun’s gravitational pull on the Earth’s ocean. The major cause of tide is the Moon’s gravitational force. There are two bulges one on the side of the Earth-facing the moon and the other on the opposite side. As Earth’s rotates each point on its surface passes through two high tides and low tides and low tides each day.

The effect of the Sun’s gravity on the oceans is only half that of the Moon’s. However, when they are aligned (Every 14.5 days) their pulls reinforce and create spring tides when the tidal range is the greatest. Thus spring tides occur on full moon day and new moon day.

When the sun and moon are at right angles to Earth, their pulls offset each other and neap tides result. At this time the tidal range is the minimum.

Calculation Moon’s Rising Time:

Example – 01:

Moon’s rising time is at 8.00 p.m. on 4 th January. Find rising times of it on the following days. a) 3 rd January b) 1 st January  c) 5 th January d) 9 th January

Solution:
We know that on any day it rises about 50 minutes later than the previous day.

a) 3 rd January

4 th January – 3 rd January = 1 day
The rising time of it on 3 rd January
= 8.00 p.m. – 1 x 50 minutes
= 8.00 p.m. – 50 minutes
= 7.10 p.m.
Therefore, the moon’s rising time is  at 7.10 p.m. on 3 rd January

b) 1 st January

4 th January – 1 st January = 3 days
The rising time of it on 1 st January
= 8.00 p.m. – 3 x 50 minutes
= 8.00 p.m. – 150 minutes
= 8.00 p.m. – 2 hrs 30 minutes
= 5.30 p.m.
Therefore, the moon’s rising time is at 5.30 p.m. on 1st January

c) 5 th January

5 th January – 4 th January = 1 day
Rising time of it on 5 th January
= 8.00 p.m. + 1 x 50 minutes
= 8.00 p.m. + 50 minutes
= 8.50 p.m.
Therefore, the moon’s rising time is at 8.50 p.m. on 5 th January

d) 9 th January

9 th January – 4 th January = 5 days
Rising time of it on 9 th January
= 8.00 p.m. + 5 x 50 minutes
= 8.00 p.m. + 250 minutes
= 8.00 p.m. + 4 hrs 10 minutes
= 12.10 a.m.
Therefore, the moon’s rising time is at 12.10 p.m.on 9th January

Example – 02:

On a certain day, the moon rises at 11.25 p.m. At what time will it rise the next day? At what time it risen the day before.

Solution:
We know that, on any day the moon rises about 50 minutes later than the previous day.

a) next day (+1)

4 th January – 3 rd January = 1 day
Rising time of it on the next day
= 11.25 p.m. + 1 x 50 minutes
= 11.25 p.m. + 50 minutes
= 12.15 a.m.

b) the day before (-1)

3 rd January – 2 nd January = 1 day
Rising time of it on the next day
= 11.25 p.m. – 1 x 50 minutes
= 11.25 p.m. – 50 minutes
= 10.35 p.m.
Therefore, the moon’s rising time is at 12.15 a.m. on the next day and risen at 10.35 p.m. the day before.

Calculation of Weight of Bodies:

Example – 01:

The weight of a body on the surface of the Earth is 60 N. What is its weight on the surface of the moon?

Solution:

We know that the gravity on the surface of the moon is one-sixth that on the surface of the Earth.

Hence, Weight of body on the moon
= (1/6) x Weight on the surface of the Earth
= (1/6) x 60 N = 10 N
Therefore, the weight of the body on the surface of the moon is 10 N.

Example – 02:

The weight of a body on the surface of the moon is 12 N. What is its weight on the surface of the Earth?

Solution:

We know that the gravity on the surface of the moon is one-sixth that on the surface of the Earth.

Hence, Weight of body on the Earth
= 6 x Weight on the surface of the moon
= 6 x 12 N = 72 N
Therefore, the weight of the body on the surface of the Earth is 72 N.

Example – 03:

A body of mass 15 kg on the surface of the Earth is taken on the surface of the moon. What is its mass on the surface of the moon?

Solution:

We know that the mass of a body is constant. It does not change with the place. Hence the mass of the body on the surface of the moon will be the same as that on the surface of the Earth i.e. 15 kg.

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