The Universe

Syllabus: Night sky, milky way, galaxy, structure of universe and its theories.

Space Exploration- (a brief history): Elementary ideas about space launching vehicles; different types of artificial satellites and their orbits, applications of artificial satellites in communications, weather monitoring, remote sensing; space science programmes in India ( an overview)


Night Sky -Up to about 3,000 stars are visible at a time from Earth with the unaided eye, far away from city lights, on a clear night. A view at night may also show several planets and perhaps a comet or a meteor shower.

☼ The Pole Star appears fixed because it is along the direction of the axis of rotation of the earth.

☼ Easily recognizable constellations are the Big Bear, Orion, Taurus, Libra.

☼ The Pole Star defines the direction we call the North.

Milky wayMilky Way, the large, disk-shaped aggregation of stars, or galaxy, that includes the Sun and its solar system.

Galaxy – A galaxy is a system of stars, dust, and gas held together by gravity. Our solar system is in a galaxy called the Milky Way.

Types of galaxy: There are three kinds of galaxies. They are (i) spiral galaxies, (ii) elliptical galaxies and (iii) Irregular galaxies.

A spiral galaxy is shaped like a disk with a bulge in the center. The Milky Way is a spiral galaxy.

Elliptical galaxies range in shape from almost perfect spheres to flattened globes. The light from an elliptical galaxy is brightest in the center and gradually becomes fainter toward its outer regions.

Galaxies of a third kind, irregular galaxies, lack a simple shape.

Structure of Universe

Hubble’s Law: According to Hubble’s Law, galaxies are rushing away from our galaxy. The velocities with which they are rushing away from us, increase as their distances increase from us.

Hubble’s Law is basis for the belief that the universe is fairly uniformly expanding.

Origin of Universe – Theories————————————————————–

Big Bang Theory: The big bang theory describes a hot explosion of energy and matter at the time the universe came into existence. This theory explains why the universe is expanding. he work of Edwin Hubble, which showed that the universe is expanding. A huge explosion took place at that time, and since then, the universe is expanding. It has been estimated that this event occurred about 15 billion (15×109) years ago. This means that the universe is about 15 billion years old.

Steady State Theory: According to the steady state theory, the universe appears to be same at all times and at all points and it does not have a beginning and will not have an end.

Space Exploration——————————————————————–

Brief History: The era o space exploration started in 1957, when Russian scientists succeeded in launching an artificial satellite in outer space.

NASA – National Aeronautic and Space Administration (of USA)

Launch Vehicles :

☼ The first stage of a multistage rocket consists of rocket engines that provide a huge amount of force, or thrust. The first stage lifts the entire launch vehicle-with its load of fuel, the rocket body, and the satellite-off the launch pad and into the first part of the flight. After its engines use all their fuel, the first stage portion of the rocket separates from the rest of the launch vehicle and falls to Earth.

☼ The second stage then ignites, providing the energy necessary to lift the satellite into orbit. It, too, then separates from the satellite and any remaining rocket stages.

☼ The rest of the launch depends on the satellite’s mission. For example, if the mission requires a geostationary orbit, which can be achieved only at a distance of about 35,000 km (22,000 mi) above Earth, a third rocket stage provides the thrust to lift the satellite to its final orbital altitude. After the satellite has reached the final altitude, another rocket engine fires and gives the satellite a circular orbit.

Payload: The weight of instruments carried in a satellite for various tasks is called payload.

The essential properties of rocket fuels are:-

(i) it must burn very rapidly but not explode; and

(ii) it must produce large volumes of gas at high pressure and temperature

The fuel generally used is a mixture of liquid hydrogen and liquid oxygen.

Types of Artificial Satellites———————————————————————-

Artificial Satellite is any object place into orbit around earth, other planets of the Sun. They are also called the ‘eyes in the sky’. The minimum velocity required to launch an artificial satellite in an orbit is around the earth is about 8 km/s. The minimum height of an artificial satellite is 200 km.

The artificial satellites are of 3 basic types:-

(i) Communications satellite

(ii) Weather monitoring satellites;

(iii) Remote sensing satellites; and

(iv) Scientific satellites

Communication satellites: They are artificial satellites which transmit telephone and television signals over long distances.

Weather monitoring satellites: They are artificial satellites which are used for weather forecasting.

Remote sensing satellites: Remote Sensing is process of obtaining information about land, water, or an object, without any physical contact between the sensor and the subject of analysis. The term remote sensing most often refers to the collection of data by instruments carried aboard aircraft or satellites. The satellites used for remote sensing are called remote sensing satellites.

Scientific satellites: Artificial satellites used for scientific purposes are called scientific satellites. Eg. Hubble Space Telescope, Chandra X-ray satellite

Orbits of Artificial satellites———————————————————————-

Geostationary (also called Equatorial) orbits: Satellites in geostationary equatorial orbit , orbit Earth around the equator at a very specific altitude that allows them to complete one orbit in the same amount of time that it takes Earth to rotate once. Communication satellites use geostationary orbits.

Polar Orbits: Satellites used for weather forecasting and remote sensing, have orbits passing over the poles of the earth. Such orbits are called polar orbits. These orbits are at a height o about a 1000 km from the earth’s surface.

Space Science programmes in India————————————————————-

ISRO – Indian Space Research Organisation

Some ISRO Programmes

☼ Indian National Satellite System (INSAT) series of satellites.

INSAT -1, INSAT – 2 and INSAT – 3 series.

☼ Indian Remote Sensing Satellite (IRS) system

IRS – 1 series and IRS – P series.

IRS data is marketed commercially.

METSAT for weather monitoring.

☼ Rohini Satellite Series for astronomical observations.

☼ Polar Satellite Launch Vehicle (PSLV) developed and tested successfully. It is now available for launching 1000 – 2000 kg class of remote sensing satellites.

☼ Geosynchronous Satellite Launch Vehicle (GSLV) has already been tested successfully.

(Sources of Information: Microsoft Encarta, 2001, Worldbook, Wikipedia, NASA website.)

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