Universe Questions in English

(B) The tail of a comet is formed by the solar wind and radiation pressure from the Sun. As the comet approaches the Sun,these forces push the gas and dust particles away from the comet's nucleus. Consequently,the tail always points away from the Sun,regardless of the direction in which the comet is moving.

(A) The angle of elongation $\varepsilon$ is the angle formed at the Earth between the direction of the planet and the direction of the Sun.
When the planet appears at its maximum elongation,the line of sight from Earth is tangent to the planet's orbit. Consequently,the angle subtended by the Sun and Earth at the planet is $90^\circ$.
From the geometry of the right-angled triangle formed by the Sun $(S)$,the planet $(P)$,and the Earth $(E)$:
$\cos \varepsilon = \frac{\text{Adjacent}}{\text{Hypotenuse}} = \frac{r_{PS}}{r_{ES}}$
Given $\varepsilon = 47^\circ$ and $r_{ES} = 1 \ AU$ (distance from Earth to Sun),
$r_{PS} = r_{ES} \cos 47^\circ$
$r_{PS} = 1 \ AU \times \cos 47^\circ \approx 1 \times 0.682 = 0.68 \ AU$.
Therefore,the distance of Venus from the Sun is approximately $0.68 \ AU$.

(C) The solar system consists of the Sun and the objects that orbit it. The Sun is the only star in our solar system. Therefore,the number of stars is $1$.

(C) Black Hole is a region of spacetime exhibiting gravitational acceleration so strong that nothing—no particles or even electromagnetic radiation such as light—can escape from it. It is formed due to the continued gravitational collapse of the core of a massive star during a supernova explosion,resulting in a super dense object.

(D) Time taken by quasar light to reach Earth $= 3 \text{ billion years} = 3 \times 10^9 \text{ years}$.
Converting time into seconds:
$t = 3 \times 10^9 \times 365.25 \times 24 \times 60 \times 60 \text{ s} \approx 9.467 \times 10^{16} \text{ s}$.
Speed of light $c = 3 \times 10^8 \text{ m/s}$.
Distance $d = c \times t = (3 \times 10^8 \text{ m/s}) \times (9.467 \times 10^{16} \text{ s}) = 2.84 \times 10^{25} \text{ m}$.
Converting meters to kilometers $(1 \text{ km} = 10^3 \text{ m})$:
$d = 2.84 \times 10^{22} \text{ km}$.

(N/A) The Ptolemaic model,proposed by Claudius Ptolemy in the $2^{nd}$ century $AD$,is a geocentric model of the universe.
$1$. It posits that the Earth is stationary at the center of the universe.
$2$. All celestial bodies,including the Sun,Moon,planets,and stars,revolve around the Earth in complex circular paths.
$3$. To explain the observed retrograde motion of planets (where they appear to move backward in the sky),Ptolemy introduced the concept of 'epicycles'.
$4$. In this system,each planet moves in a small circle called an 'epicycle',while the center of this epicycle moves along a larger circular path around the Earth called a 'deferent'.
$5$. This model was the dominant cosmological framework for over $1,400$ years until it was replaced by the heliocentric model proposed by Nicolaus Copernicus.

(N/A) Aryabhatta,a renowned ancient Indian mathematician and astronomer,proposed a revolutionary model for planetary motion in his work,the $Aryabhatiya$.
$1$. He correctly postulated that the Earth rotates on its own axis from west to east.
$2$. He explained that the apparent motion of stars and planets from east to west is due to the rotation of the Earth.
$3$. He suggested that the planets move in circular orbits around the Sun,which was a significant departure from the prevailing geocentric models of his time.
$4$. He also provided accurate calculations for the periods of planetary rotation and revolution,demonstrating a deep understanding of celestial mechanics long before modern astronomy.

(N/A) The size of an atomic nucleus is approximately $10^{-14} \,m$.
The size of the observable universe is approximately $10^{26} \,m$.

(N/A) The masses of objects encountered in the universe vary over a very wide range.
These masses range from the order of $10^{-30} \ kg$ (mass of an electron) to the huge mass of $10^{55} \ kg$ (mass of the observable universe).

Object	Mass $(kg)$
Electron	$10^{-30}$
Proton	$10^{-27}$
Uranium atom	$10^{-25}$
Red blood cell	$10^{-13}$
Dust particle	$10^{-9}$
Rain drop	$10^{-6}$
Mosquito	$10^{-5}$
Grape	$10^{-3}$
Human	$10^{2}$
Automobile	$10^{3}$
Boeing $747$ Aircraft	$10^{8}$
Moon	$10^{23}$
Earth	$10^{25}$
Sun	$10^{30}$
Milky Way galaxy	$10^{41}$
Observable universe	$10^{55}$

(A) The mass of an electron is approximately $m_e \approx 9.1 \times 10^{-31} \,kg$.
The mass of the observable universe is approximately $M_u \approx 10^{55} \,kg$.
The ratio of the mass of the observable universe to the mass of an electron is given by:
Ratio $= \frac{M_u}{m_e} \approx \frac{10^{55}}{10^{-31}} = 10^{55 - (-31)} = 10^{86}$.
Rounding to the nearest order of magnitude, the ratio is approximately $10^{85}$.

(N/A) The distance to the boundary of the observable universe is approximately $10^{26} \ m$ (maximum length).
The size of a proton is approximately $10^{-15} \ m$ (minimum length).
Therefore,the ratio is calculated as:
$\text{Ratio} = \frac{10^{26} \ m}{10^{-15} \ m} = 10^{26 - (-15)} = 10^{41}$.

(A) The maximum mass of the observable universe is approximately $10^{55} \ kg$.
The mass of an electron is approximately $9.1 \times 10^{-31} \ kg$,which is of the order of $10^{-30} \ kg$.
The ratio of the maximum mass to the mass of an electron is:
$\text{Ratio} = \frac{10^{55} \ kg}{10^{-30} \ kg} = 10^{55 - (-30)} = 10^{85}$.
Thus,the correct option is $A$.

(B) Red Giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution.
As the star exhausts the hydrogen fuel in its core,the core contracts and heats up,causing the outer layers of the star to expand and cool.
This expansion gives the star a reddish appearance and a significantly larger radius compared to its main-sequence phase.
Therefore,it is a dying star that has moved off the main sequence.

(N/A) Inferior planets are those planets whose distance from the Sun is less than the distance of the Earth from the Sun.
Elongation of a planet is defined as the angle subtended at the Earth by the line joining the Earth to the Sun and the line joining the Earth to the planet,as they revolve in their respective orbits around the Sun.

(A) The first Indian astronaut to travel into space is $Rakesh$ $Sharma$. He flew aboard the Soviet spacecraft $Soyuz$ $T-11$ on $April$ $3, 1984$.

(A) The solar system consists of the Sun at the center,with eight planets orbiting it. The order of the planets starting from the Sun is:
$1$. Mercury
$2$. Venus
$3$. Earth
$4$. Mars
$5$. Jupiter
$6$. Saturn
$7$. Uranus
$8$. Neptune
This sequence is based on their average distance from the Sun. Therefore,option $A$ is the correct sequence.

(A) The evolution of the universe follows a specific chronological sequence:
$1$. $Big \ Bang$: The initial expansion of the universe.
$2$. $Inflation$: $A$ period of extremely rapid expansion occurring shortly after the Big Bang.
$3$. $Nucleosynthesis$: The formation of light elements (like Hydrogen and Helium) in the early universe.
$4$. $Recombination$: The epoch when electrons and protons combined to form neutral atoms,allowing light to travel freely (Cosmic Microwave Background).
$5$. $Star \ Formation$: The later stage where gravity caused matter to clump together to form stars and galaxies.
Thus,the correct order is $Big \ Bang \rightarrow Inflation \rightarrow Nucleosynthesis \rightarrow Recombination \rightarrow Star \ Formation$.

(D) The solar system consists of the Sun and the objects that orbit it,including eight planets.
Among these,Mars is famously known as the 'Red Planet' due to the prevalence of iron oxide (rust) on its surface,which gives it a reddish appearance.
Therefore,the correct option is $D$.

(A) lunar eclipse occurs only when the Earth is positioned between the Sun and the Moon,which happens exclusively during a full moon phase.
Option $(A)$ states that a lunar eclipse can occur on a new moon and full moon day,which is false because a new moon occurs when the Moon is between the Earth and the Sun.
Option $(B)$ is true because the orbital planes of the Earth and Moon are inclined at an angle of about $5^{\circ}$. If they were coplanar,the alignment would occur every month.
Option $(C)$ is true as the Earth's atmosphere scatters shorter wavelengths (blue) and allows longer wavelengths (red) to pass through,which then illuminate the Moon.
Option $(D)$ is true as it correctly identifies the phase required for a lunar eclipse.
Therefore,the statement that is not true is $(A)$.

(C) The correct option is $C$.
During a total solar eclipse,the Moon passes between the Sun and the Earth,casting its shadow on a small region of the Earth's surface.
The size of the Moon is much smaller than that of the Earth. Furthermore,the Moon is significantly closer to the Earth compared to the Sun.
Consequently,the shadow cast by the Moon on the Earth is relatively small,covering only a tiny portion of the Earth's visible disk as seen from the Moon. This is represented by the small shaded region within the larger circle $E$ in option $C$.

(C) The axis of rotation of the Earth is the imaginary line passing through the North and South Poles. When this axis is extended into space from the North Pole,it points very close to Polaris,which is commonly known as the Pole Star or the North Star. Due to the Earth's axial precession,this alignment changes very slowly over thousands of years,but at present,it passes very close to Polaris.

(A) The actual average life of a human is approximately $70$ years,which is about $2.2 \times 10^9 \, s$. For the purpose of order of magnitude,we take it as $10^9 \, s$.
The actual age of the universe is approximately $13.8$ billion years,which is about $4.35 \times 10^{17} \, s$. For the purpose of order of magnitude,we take it as $10^{17} \, s$.
Let the scale factor be $k$. According to the problem,the human life on this scale is $100 \, s$.
Therefore,$k \times (10^9 \, s) = 100 \, s$,which gives $k = 10^{-7}$.
Now,the age of the universe on this scale is $k \times (10^{17} \, s) = 10^{-7} \times 10^{17} \, s = 10^{10} \, s$.

(A) The flash spectrum is a series of bright emission lines observed in the solar spectrum for a few seconds during a total solar eclipse. When the moon completely covers the bright photosphere of the sun,the thin layer of the chromosphere becomes visible,producing this unique emission spectrum.

(C) In the astronomical magnitude scale,the brightness of stars is classified by their apparent magnitude. The brightest stars have lower (or negative) magnitude values,while the faintest stars visible to the human eye under ideal conditions are classified as sixth magnitude stars.

(B) The greenhouse effect is a natural process that warms the Earth's surface.
When the Sun's energy reaches the Earth's atmosphere,some of it is reflected back to space and the rest is absorbed and re-radiated by greenhouse gases.
Without these naturally occurring greenhouse gases,the Earth's average surface temperature would be approximately $-18^{\circ} C$,which is significantly colder than the current average of about $+15^{\circ} C$.