Universe And Space Online Test 7th Science Lesson 13 Questions in English

Explanation

“My goal is simple. It is a complete understanding of the universe, why it is as it is and why it exists
at all.”—Stephen Hawking

Explanation

The field of study of the universe is called astronomy.

Explanation

Universe is commonly defined as the totality of everything that exists or is known to exist. Even
though the spatial size of the entire universe is still unknown, it is possible to measure the
observable universe.

Explanation

The universe consists of galaxies, planets, stars, meteorites, satellites and all other forms of matter and energy. And it is a world of wonder.

Explanation

Sky is a wonder. Sun, Moon, stars all appear to rise in the East and move towards the west giving us an impression that all these objects are going around the Earth.

Explanation

The Sun appears to revolve around the Earth once in a day. While the Moon and the planets have their own motions they also appear to revolve around the Earth about once per day. Even the celestial sphere studded with stars appears to rise and set in the evening, and make one complete
rotation in a year.

Explanation

The Earth seems to be unmoving from the perspective of an earthbound observer, it feels stationary.

Explanation

On a daily basis Moon appears to rise in the east and set in the west. Thus one can say that Moon
is going around the Earth with a period of one day.

Explanation

Everyday Moon appears to move from east to west in one day where as it appears to go in a circle
from west to east in the background of stars in about 27 days.

Explanation
Astronomers like Aryabhatta said that Earth is spinning in its axis that is the cause of apparent daily motion from East to West. Whereas the eastward motion of Moon in the celestial sphere with a period of about 27 days was seen as the ‘actual’ motion of the celestial objects.

Explanation

The geocentric model (also known as geo-centrism), that is a description of the Universe with
spherical and spinning Earth at the center and the Sun, Moon, stars, and planets all orbits the Earth
emerged in various cultures.

Explanation

In Greece the geocentric model was put forth by the Greek philosopher Plato and his disciple Aristotle in 6th century B.C. It was standardized by a Greeco-Roman mathematician Ptolemy in the 2nd Century A.D. A similar model is seen in the Siddhanthic astronomy in India like Aryabhateeyam of Aryabhata.

Explanation

Astronomers in ancient times also observed certain facts. The Purananuru (65) of Sangam literature, the poet Kalathalaiyar singing in appreciation of Cheraman Peruncheralathan says“ On the day when the full moon appears, the sunand moon look at each other with their bright light. In the evening time, one sphere hides behind the mountains.”

Explanation

On the full moon day, when the Sun is setting in the west, precisely at the same time Moon rises at the East. That is both Sun and Moon are in the opposite side.

Explanation

It is probably easier to understand the waxing and waning of Moon in the order of new moon & full moon and then how the first and third quarter moon (half-moon) appear and then the phases in between.

Explanation

Sun is the source of light. Sun light falls on the spherical earth, but only on the side facing Sun. The
opposite side of Earth is without sunlight. As the Earth spins day and night follows as different
parts of Earth appear before the Sun. That is at all times one half of Earth is illuminated by Sun and
one half is in darkness.

Explanation

When the moon is positioned between the earth and sun notice all the illuminated part of Moon is away from Earth. Hence we cannot see any part of the illuminated side of the Moon. Only the dark side of Moon is towards Earth. When the moon is in this position, we have new moon.

Explanation

The moon when it is behind the Earth. Now the portion of the moon illuminated by sun is totally
towards Earth. The dark side is away from the Earth. This means the moon will appear to be round in the sky. This is full moon

Explanation

When the moon facing Earth half if it illuminated and half is dark side. Thus the moon will appear as half-moon.

Explanation

The half-moon during the waxing period is called as first quarter and the half-moon during the
waning period is called as third quarter.

Explanation

The word crescent refers to the phases where the moon is less than half illuminated.

Explanation

The word gibbous refers to phases where the moon is more than half illuminated.

Explanation

In the phases of the moon waxing essentially means “growing” or expanding in illumination and
waning means “shrinking” or decreasing in illumination.

Explanation

Moon going around Earth with 27 day period nicely explained its motion. Astronomers in ancient times faced problem in explaining the motion of the then known five planets- Mercury, Venus, Mars, Jupiter and Saturn.

Explanation

On June 28 a change is seen. From that date the Mars would appear to move west rather than its
normal eastward motion. This reversal of direction of planets is called as ‘retrograde motion’.

Explanation

Usually Jupiter is brighter than Mars, however around the period of retrograde motion the Mars
was much bright than other times; even brighter than Jupiter.

Explanation

Venus and Mercury always appeared very close to Sun and hence never appeared in the midnight
sky.

Explanation

The brightness of Jupiter also varied again when it exhibited retrograde motion. For example in 2018, Jupiter reversed its direction of motion on March 9, 2018 and again resumed its normal eastward motion on July 11, 2018.

Explanation

The simple geocentric model, where planets go around the Earth could not explain why the brightness of the planets changed, and why they reversed their directions. Change in brightness and retrograde motion would be impossible if we assumed that the planets were at the same
distance at all times from Earth.

Explanation

Ptolemy (2nd cent) in Greece Aryabhatta in India and others used the epicycle model to explain the
motion of the celestial objects.

Explanation

Their models were improved by generation of astronomers like Tycho Brahe and Neelakanta
Somayaji.

Explanation

Telescope was invented by Hans Lippershey but Galileo used it for studying the sky for the first
time. The telescope showed more universes were than visible to naked eye.

Explanation

One of the most startling observations Galileo made was related to telescopic observation of Venus.
This convinced him to accept the theory of Sun- heliocentric theory. The Polish Astronomer
Nicolas Copernicus that it is not Sun, planets and Stars that go around Earth, but it is Earth and
other planets that go around the Sun- heliocentric theory.

Explanation

Dissatisfied with the messy epicycle model Nicolus Copernicus radically proposed that the model
will become simple if we assume Sun is at the center and all planets including Earth go around it.

Explanation

Earth orbit around Sun in 365 days whereas Mars takes 687 days. This implies at times Earth will
overtake Mars. When the Earth is approaching and overtaking Mars, the Mars would appear to exhibit retrograde motion.

Explanation

Galileo observed Venus in 1610-1611 with a telescope. To naked eye Venus is just a gleaming bright spot. However, through a telescope, the shape of the planet can be seen. Galilio was startled to find
like Moon Venus too exhibited phases. The shape varied from crescent to gibbous. Also, the size of the planet varied. When the planet was in gibbous phase the size was small, and when it was thin crescent the size was many folds higher.

Explanation

Our Sun is a star with a planetary system. Billions of such stars constitute a system called as galaxy.
The name of our galaxy is, Milky Way. Like Milky Way, there are at least hundreds of billions of galaxies in the Universe.

Explanation

The Cosmologist’s scientists who study the structure and evolution of universe that is cosmos,
reason that this imply at one point of time in the past all matter was confined in a single point and
since then it has started to expand. The event when the matter confined in a single point and began
to expand is called ‘big bang’. This is considered as the origin of our universe as we know it.

Explanation

The Big Bang Theory is the prevailing model of the evolution of the Universe. Under this theory,
space and time emerged together about 14 billions of years ago. At that time, the entire Universe was inside a bubble that was thousands of times smaller than a pinhead. It was hotter and denser than anything we can imagine. Then it suddenly expanded. The present Universe emerged .Time,
space and matter all began with the Big Bang.

Explanation

At the stage of the evolution of the Universe, it was filled with clouds of hydrogen and helium gas. Giant clouds of hydrogen and helium were gradually drawn to the places where dark matter was most dense, forming the first galaxies, stars, and everything else seen today.

Explanation

We cannot see anything that happened during the first 300000 years of the Universe. Scientists try to work it out from their knowledge of atomic particles and from computer models. The only direct evidence of the Big Bang itself is a faint glow in space, called cosmic microwave background.

Explanation

Finally, about 100 million years after the Big Bang, the gas became hot and dense enough for the
first stars to form. New stars were being born at a rate 10 times higher than in the present-day
Universe. Large clusters of stars soon became the first galaxies.

Explanation

The Universe is constituted of galaxies; just as lot of houses in our locality constitute a village or a city. We have lot of things such as rooms, furniture etc. in our homes. Likewise lot of stellar objects
such as stars, planets, asteroids and meteors are the building blocks of our universe.

Explanation

Astronomical unit: The average distance between the Earth and the Sun is called an astronomical
unit. It is denoted by ‘au’. 1 au = 1.496 x 108km
Light year: The distance travelled by light in one year is called a light year. It is denoted by ‘ly’. 1 ly
= 9.4607 x 1012 km
Parsec: A parsec is defined as the distance at which one astronomical unit subtends an angle of
one arc second. It is denoted by ‘pc’
1 pc = 3.2615 ly = 3.09 x 1013 km

Explanation

A galaxy is a large collection of stars or cluster of stars and celestial bodies held together by
gravitational attraction. There are about billions of galaxies in the universe. Most galaxies range
from thousand to ten thousand parsec in diameter.

Explanation

Types of galaxies: There are various types of galaxies such as spiral, elliptical, barred spiral and
irregular.

Explanation

Spiral galaxies consist of a flat, rotating disk containing stars, gas and dust, and a central concentration of stars known as the bulge. These are often surrounded by a much fainter halo of stars. Spiral galaxies are named by their spiral structures that extend from the center into the galactic disc. The spiral arms are sites of ongoing star formation and are brighter than the
surrounding disc because of the young, hot stars that inhabit them.

Explanation

An elliptical galaxy is a type of galaxy having an approximately ellipsoidal shape and a smooth
image. Unlike flat spiral galaxies with organization and structure, elliptical galaxies are three-
dimensional, without much structure and their stars are in somewhat random orbits around the center. Interestingly Stars found inside of elliptical galaxies are on an average much older than stars found in spiral galaxies. Elliptical galaxies tend to be surrounded by large numbers of globular clusters.

Explanation

An irregular galaxy is a galaxy that does not have a distinct regular shape, unlike a spiral or an
elliptical galaxy they are often chaotic in appearance, with neither a nuclear bulge nor any trace of
spiral arm structure. About one-fourth of the galaxies found so far are of this type. Irregular galaxies
may contain abundant amounts of gas and dust.

Explanation

Cosmologists say that some irregular galaxies were once spiral or elliptical galaxies but were
deformed by an uneven external gravitational force.

Explanation

The Milky Way Galaxy where our own Solar System is located is classified as a barred spiral galaxy.

Explanation

The Milky Way is the galaxy in which our solar system is located. The diameter of Milky Way is over 100,000 light years.

Explanation

The Milky Way includes stars smaller than our Sun as well as many other stars that are thousands of times bigger than the Sun. It includes many other celestial bodies of gases, clouds of dust, dead stars, newly born stars, etc. It is also thought to contain at least 100 billion stars.

Explanation

The galaxy that is closest to our Milky Way is Andromeda. The descriptive “milky” is derived from
the appearance from Earth of the galaxy – a band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye.

Explanation

Galileo Galili first resolved the band of light into individual stars with his telescope in 1610.

Explanation

Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the
Universe. Observations by Edwin Hubble showed that the Milky Way is just one of many galaxies.

Explanation

The solar system travels at an average speed of 828,000 km/h. Even at this rapid speed, the solar
system would take about 230 million years to travel all the way around the Milky Way.

Explanation

Tucked inside the very center of the galaxy is a monstrous black hole, billions of times as massive
as the sun. Although, black holes cannot be directly viewed, scientists can see their gravitational effects as they change and distort the paths of the material around it most galaxies like our milky way, are thought to have a black hole in their heart.

Explanation

A constellation is a recognizable pattern of stars in the night sky when viewed from the Earth.
International Astronomical Union has classified 88 constellations to cover the entire celestial
sphere. Many of the old constellations have Greek or Latin names and are often named after
mythological characters.

Explanation

Ursa Major (Saptha Rishi Mandalam) is a large constellation and it covers a large part of the sky.
The most striking feature of this constellation is a group of seven bright stars known as big dipper
(seven Sages in Indian astronomy).

Explanation

Ursa Minor in Latin means ‘the little bear’ it lays in the northern sky. The Pole star – Polaris (Dhrua)
lies within this constellation. The main group, ‘little dipper’ consists of seven stars and is quite
similar to that found in Ursa Major.

Explanation

Different constellations become visible in the sky at different times in the year. This happens due
to the revolution of the Earth around the Sun.

Explanation

Unlike galaxy, constellations are mere optical appearance and not real objects. In galaxy stars are
bound by gravity and constitute a system. In a constellation, one star may be near and another veryfar, but because they are in the same direction appear to be near to each other in the sky.

Explanation

A Star is a luminous heavenly body that radiates energy. With naked eyes, we can see nearly 3000
stars in the night sky and many more with the help of a telescope. The stars are remotely located and appear as tiny dots of light. Their light travels long distances to reach us. The atmosphere disturbances do not allow light to reach us in a straight line path. Because of this the stars appear to twinkle.

Explanation

The Sun is the nearest star to the Earth. The next nearest star is Alpha Centauri

Explanation

An object that revolves around a planet in a stable and consistent orbit is called a satellite. Satellites can be classified into two categories –natural and artificial.

Explanation

All natural objects revolving around a planet are natural satellites. They are also called moons. Most
moons are spherical, the ones that are not usually asteroids or meteors that were captured by the strong gravity of a planet.

Explanation

All planets except mercury and Venus in our solar system have moons. Earth has only one moon whereas planets like Jupiter and Saturn have more than 60 moons.

Explanation

The world’s first artificial satellite launched was Sputnik-1 by Russia,

Explanation

Aryabhatta was the first satellite launched by India. These satellites are used in television and
radio transmission, studying agriculture yield, locating mineral resources, weather forecasting,
locate different places on earth.

Explanation

The Indian Space Research Organization (ISRO) is the space agency of the Government of India
headquartered in the city of Bangalore. Its vision is to “harness space technology for national
development while pursuing space science research and planetary exploration.”

Explanation

Subrahmanyan Chandrasekhar (19October 1910 – 21 August 1995) was an Indian American astrophysicist who spent his professional life in the United States. He was awarded the 1983 Nobel
Prize for Physics with William A Fowler. His mathematical treatment of stellar evolution yielded many of the best current theoretical models of the later evolutionary stages of massive stars and black holes. The Chandrasekhar limit is named after him. Chandrasekhar worked on a wide variety of physical problems in his lifetime.

Explanation

Formed in 1969, ISRO superseded the erstwhile Indian National Committee for Space Research (INCOSPAR) established in 1962 by the Scientist Vikram Sarabhai. The establishment of ISRO thus institutionalized space activities in India. It is managed by the Department of Space, which reports to the Prime Minister of India.

Explanation

ISRO built India’s first satellite, Aryabhatta which was launched by the Soviet Union on 19 April 1975. It was named after the Indian astronomer Aryabhata.

Explanation

In 1980, Rohini became the first satellite to be placed in orbit by an Indian-made launch vehicle,
SLV-3. ISRO subsequently developed two other rockets: the Polar Satellite Launch Vehicle (PSLV)
for launching satellites into polar orbits and the Geosynchronous Satellite Launch Vehicle (GSLV)
to place satellites into geostationary orbits.

Explanation

Satellite navigation systems like GAGAN and IRNSS have been deployed. In January 2014, ISRO used an indigenous cryogenic engine in a GSLV-D5 launch of the GSAT-14.

Explanation

ISRO sent a lunar orbiter, Chandrayan -1 on 22 October 2008 and a Mars orbiter, Mars Orbiter Mission, on 5 November 2013, which entered Mars orbit on 24 September 2014, making India the first nation to succeed on its first attempt to Mars, and ISRO the fourth space agency in the world
as well as the first space agency in Asia to reach Mars orbit.

Explanation

On 15 February 2017, ISRO launched 104 satellites in a single rocket (PSLV-C37) and created a world record. ISRO launched its heaviest rocket, Geosynchronous Satellite Launch Vehicle- Mark III (GSLV-Mk III) on 5 June 2017 and placed a communications satellite GSAT-19 in orbit. With this launch, ISRO became capable of launching 4 ton heavy satellites.

Explanation

ISRO launched Chandrayan 2 on July 22, 2019, Geosynchronous Satellite Launch Vehicle (GSLV-Mk III). It entered the Moon’s orbit on August 20, 2019 and its lander landed on the Moon on September 7.

Explanation

In 1989, Galileo Galilei was memorialized with the launch of a Jupiter-bound space probe bearing
his name. During its 14-year voyage, the Galileo space probe and its detachable mini-probe, visited
Venus the asteroid Gaspra, observed the impact of Comet Shoemaker-Levy 9 on Jupiter, Europa, Callisto, IO, and Amalthea. In order to avoid the possible contamination of one of Jupiter’s moons, the Galileo space probe was purposely crashed into Jupiter at the end of its mission in September 2003.

Explanation

After completing studies at MIT, Abdul Kalam designed an aircraft named ‘Nandhi’ using indigenous materials with the help of indigenous technologists, He operated that flight himself.

Explanation

Kalam successfully launched the ‘Rohini-1’ satellite using the India’s first satellite launch vehicle SLV-3 in 1980. He acted as the Project Director when the missiles Thrishul, Agni, Prithvi, Nag and Akash were designed in the Indian Defence.

Explanation

India for the first time experimented nuclear explosion test named ‘Smiling Buddha’ in 1974. Kalam was one among the sixty Aeronautical Engineers in this project.

Explanation

Abdul Kalam played a vital role in the nuclear explosion test project in Pokran named “Operation Sakthi” in 1999. The credit that the India has become a nuclear power goes to him.

Explanation

Abdul Kalam played a vital role in the nuclear explosion test project in Pokran named “Operation Sakthi” in 1999. The credit that the India has become a nuclear power goes to him.