Universe

The celestial self-luminous object which produces energy on their own in the form of radiation due to thermonuclear fusion are called Stars.

Option (B): Phobos is one of the moons of mars. It is natural satellites of Mars.

Option (C): Asteroids: - These are the rock that fails to form a planet during the formation of the solar system.

Option (D): Comet: - These are a group of celestial objects, which revolve around the sun in an elliptical orbit.

There are numerous stars of various sizes, out of which sun is one such star. In fact, the sun is the nearest star.

Artificial satellite: These are man-made satellite launched in the space for some special purpose.

And rest of the option is found naturally in our solar system, so the artificial satellite cannot be considered a part of the solar system.

76 years. Halley’s comet named after Edmond Halley. It was last seen in the year 1986 and will be seen again in 2062. So the periodic time for Halley’s comet is 2062-1986 = 76 yrs.

Temperature of the core region in the sun is about 1.5 crore K. Due to such high-temperature matter in the core region is in the plasma state.

Jupiter is considered the most brilliant planet in the solar system. It is one of the biggest planets in the solar system. Due to its brightness, this planet can be seen with the naked eyes.

It is believed that the pole of Mars is covered by dry ice (solid CO₂) this also indicates the presence of water on the Mars.

Neil Armstrong is the first person to walk on the moon, on July 20, 1969.

The revolution period of a satellite having height 35,786 from earth’s surface is 24 hours. So any object in such an orbit appears motionless, at a fixed position in the sky, to ground observers.

The two uses of artificial satellites are as follows –

a) For communication purpose: We use artificial satellite for telecommunication, television transmission, radio network and computer network. India has launched a series of INSAT (Indian National Satellite System) for these purposes.

b) For Remote Sensing: It is the method by which we acquisition (obtain) of information about an object or phenomenon without making physical contact with the object. Using satellite we carry out a geological survey of metallic ores present in the earth crust, water resource, agriculture etc.

The celestial self-luminous object which produces energy on their own in the form of radiation due to thermonuclear fusion process is called Stars. The star seems to be permanent and of the same nature as if they don’t undergo any changes. They are of different colour the one which is red has the lowest surface temperature and the star of blue colour has the highest surface temperature.

They are made of various gases like hydrogen and helium. Star bigger in size compared to the sun have carbon-nitrogen thermonuclear fusion process in their cores.

Here is the difference between earth-centered and sun-centered models

In earlier days in the 17th century, people only have an optical telescope. So they have a limitation in using an optical telescope. In order to a deep understanding of neutron star, black hole, supernova scientist need X-ray telescope. They are not sensitive to pollution. The first x-ray telescope was launched by NASA named ‘Einstein’ later it was renamed as Chandra which sent an image from distant galaxies.

The formation and evolution of the Solar System began 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the center, forming the Sun. Thus sun contains almost 99.86% mass of the solar family. Remaining mass was flattened into the orbit, planet and moon, comet etc. By studying meteorites, which are thought to be left over from this early phase of the solar system, scientists have found that the solar system is about 4600 million years old!

Planets of the solar system with their orbit outside the orbit of Mars and composition similar to Jupiter are known as Jovian planets. These planets are bigger in size but with lesser density. They are mainly made up of hydrogen, Ammonia, and Helium. Ring are present around them. They have a moon of bigger in size.

Artificial satellite is kept in one of the following orbits-

a) Equatorial orbit: The orbits which are parallel to the equator are known as equatorial orbits.

Thus, satellite rotates in an orbit directly above the equator of Earth.

b) Polar orbit: The orbit which is parallel to the meridian is known as polar orbits. Satellites are having an inclination of near 90⁰ from the equator. This allows the satellite to see virtually every part of the Earth as the Earth rotates underneath it.

Here is a nice diagram showing both the orbit of artificial satellites:-

i. It is the first and the smallest planet of our solar system. Its mass is approximately 1/18^th mass of the earth. Its outer surface is rocky and contains mainly nickel (Ni) and iron (Fe) at the center. Due to the weak gravitational field and a short distance from the sun, it has a very thin atmosphere that contains potassium and sodium. Also, the difference between day and night temperature is very large. The side facing toward the sun is 472⁰C and opposite side -173⁰C. It has no moon.

ii. It is the second planet to our solar system and is the neighbour to the earth. It is the brightest planet. Its outer atmosphere consists of white clouds of carbon dioxide. It is the only planet that is spinning from east to west, which is in the opposite direction to other planets. Due to this sun rise in the west and set in the east. It has no moon.

iii. It is also called red planet due to reddish colour. It has a negligible atmosphere. And this atmosphere made up of mainly carbon dioxide also contain nitrogen and argon in small amounts. Its pole is covered with dry ice (solid CO₂). Phobos and Demos are two moons of mar. Here is the image of solid ice found at one of the poles of Mars -

iv. Saturn is the sixth planet from the Sun and the second largest planet.It is also called “The Ringed Planet” that is composed mostly of ice particles, with a smaller amount of rocky debris and dust. Is size is 850 times earth. Saturn is one of five planets able to be seen with the naked eye. It has three luminous rings that adds its beauty. Its surface temperature is very low. Its largest moon is Titan. Here we can see the comparison between earth and Saturn in term of its size -

v. Pluto is known as a dwarf planet. Its orbit is elliptical. It is very cold, dark and yellowish planet. The surface density is similar to that of the earth. It core contain silicate rock surrounded by water, methane and carbon monoxide in the solid form. Pluto has its moon Sheron form a binary system means they both revolve around their common center of mass.

vi. Various substances of different sizes keep on coming to the earth regularly. When they enter the earth surface they burn due to the presence of friction caused by the earth gravity and a long thin line of light can be seen, this is called a Shooting star. The falling substance are called meteors.

Sometime it is also called falling star. These are not a star (don’t confuse with the word star).

vii. All are knowing that earth takes 24 hrs to complete one rotation but this is not true actually earth takes 23 hrs and 56 minutes to complete one rotation. That’s called the sidereal day and represents the time taken for Earth to rotate relative to the fixed stars, not to the sun (because we’re orbiting our sun, so it’s not a totally stationary point relative to Earth). So in these 4 min, left star undergoes angular displacement of 1⁰. In a month of 30 days total angular displacement becomes 30⁰ and within 6-month angular displacement will be 180⁰ that means after 6 months the same star will not appear. This shows that night-sky keep on changing.

viii. The Milky Way is the galaxy that contains our Solar System. A big cluster of stars is known as a galaxy. Here cluster means a large collection of stars. During the night and in the clear sky we can see the belt of milky belt stretching from north to south. It is of spiral shape with diameter is about 1 lac light year and the thickness of the middle part is about 15 to 20 thousand light years. Most of the star in this galaxy are bluish and young.

Artificial satellites are equipped with transponders (a device for receiving and transmitting radio signal), radio mete, solar panels and necessary fuel. These satellites receive signals from the earth-station and sent to another earth-station. The signals are electromagnetic waves so they don’t get destroyed. The transmitting station sent a signal called uplink and satellite after receiving sent the signal to another station called downlink. Here is a beautiful diagram showing communication between two base station:-

Remote sensing is a method by which of we obtain information about an object or phenomenon without making physical contact with the object.

Since the artificial satellite is the main source of transmission of information. The modern satellite contains a high-resolution camera, many sensors, transponders (a device for receiving and transmitting radio signal). These cameras collect remotely sensed images of the Earth and that image is sent to the base station. Using satellite we carry out a geological survey of metallic ores present in the earth crust, water resource, agriculture etc. It is also used in oceanography and study the movement of fishes.

Additional Information:

They are two types of remote sensing:-

a) Active Remote sensing: the signal is emitted by a satellite and its reflection by the object is detected by the sensor.

b) Passive Remote sensing: when the reflection of sunlight is detected by the sensor.

The Indian Space Research Organisation is the space agency of the INDIA. Program conducted by ISRO are as follows:

a) INSAT (Indian National Satellite System) has a series INSAT 1,2,3 were launched in the space mainly for communication purpose like in TV transmission, mobile network, an internet network, GPS system etc.

b) IRS (Indian Remote Sensing) satellite which is meant for the commercial purpose.

c) PSLV (Polar Satellite Launch Vehicle) is used for launching 1000-2000 kg class of Remote Sensing satellite. This also called Medium-lift launch vehicle.

d) GSLV (Geosynchronous Satellite Launch Vehicle) launched whose weight is nearly 2500 kg.

A black hole is the region on space from which nothing can escape even the light cannot escape from it. These black holes are formed when a massive star (here massive means very large can be equivalent to our solar system) at the end of life cycle collapse in a supernova and eventually end up into a black hole. Once a black hole is formed it will continue to grow its mass by absorbing mass from its surrounding.

Around the black hole, we may image a surface called event horizon. Light reaching the event horizon is absorbed by black hole “points of no return”.

Additional information:

There are two type of event horizon:

a) outer event horizon

b) inner event horizon

Earth is the third planet from the Sun. This is the only planet in the solar family which support life. It has a thin layer of the atmosphere. The thickness of this layer is about 800 to 1000 km. This atmosphere protects us from meteors by burning and that gets converted to gaseous matter. It also contains one of the most important layers i.e. ozone layer that is responsible for absorbing ultraviolet rays of the sun. The outer layer of earth is made up of mud or rocky stones (silicate). Its core region contains semi-liquid made up of molten iron, magnesium like substance. It has one natural satellite, the moon.

An imaginary sphere covering the sky with the earth at its center is known as the celestial sphere. The ecliptic of the celestial sphere is divided into 27 equal parts, which is known as Nakshatra.

The angular displacement of each Nakshatra can be found by dividing the whole sphere i.e. 360 by 27 (360/27) we get 13⁰20’ (thirteen degrees twenty minute).

Since moon takes 27 days to complete one revolution around the earth that means moon remain in one nakshatra for a day while sun remains for 13.5 days (365/27).

Additional Information:

Nakshatra is also given names based on imaginary figure formed by joining stars.

Pushya, Ashwini, Bharani, Krittika, Rohini, Mrigashīra, Ardra, Punarvasu and 19 more.

Large collection of a celestial object around from the solar system get attracts due to the gravitational force of the sun and they start moving toward the sun, these are called comets. Most of the comets revolve around the sun in elliptical orbit.

These are mostly made of ices mixed with smaller amounts of dust and rock. Most comets are no larger than a few kilometers across. The main body of the comet is called the nucleus, and it can contain water, methane, nitrogen and other ices. When a comet is heated by the Sun, its ices begin to sublimate (similar to the way dry ice “fizzes” when you leave it in sunlight). The mixture of ice crystals and dust blows away from the comet nucleus in the solar wind, creating a pair of tails. The dust tail is what we normally see when we view comets from Earth.

The most famous comets is Halley comets. Here is the orbit of halley comet:-

Galaxies are collections of stars, dust, and gas rotating around supermassive black holes. A galaxy can range in the number of stars as well as its size. Small galaxies are called dwarf galaxies, can contain as little as tens of millions of stars whereas massive galaxies contain hundreds of trillions of stars.

There are three main types of galaxies: Elliptical, Spiral, and Irregular.

a) Elliptical galaxies: Elliptical galaxies are shaped like a spheroid (flattened shape), or elongated sphere. Most of the star in elliptical galaxies are very old and red in color. It is believed that elliptical galaxies are older than spiral galaxies. Elliptical are smaller in number and contain less dust than the spiral galaxy.

b) Spiral galaxies: The Milky Way is thought to be a spiral galaxy with a black hole at its center. Spiral galaxies comprise up to half of all the galaxies in the known universe. Most of the star are bluish and they are young.

c) Irregular galaxies: Irregular galaxies are classified into three main categories; Irr-I, Irr-II, and dIrr. It is believed that some irregular galaxies are deformed by the gravity of other galaxies.

Here are the structure of galaxy:-

The space shuttle is a reusable spacecraft designed to transport people and cargo between earth and space. It is composed of three main parts:

a) Orbital Vehicle (OV)

b) Expandable external tank (ET)

c) Two reusable solid rocket booster (SRBs)

Early day’s space shuttle is launched vertically like a rocket that revolves around the earth and comes back to earth like an airplane. After the advancement of the technology life cycle of the space shuttle, we well divided into several stages. During the flight of space shuttle, the SRBs are dropped with the help of a parachute. Since the speed of a space shuttle is very high so air friction generates a lot of heat. The outer surface of the space shuttle is made up of special alloy.