Nubra is a beautiful region in Ladakh. An eleven-year old girl Yangdol and her twin brother Dorjay live in one of the villages of this region. They love their surroundings — the majestic mountain peaks, and the glaciers, but their favourite is the night sky when the entire sky is lit up with thousands of stars (Fig. 12.1). The weather in Nubra is almost cloudless. With almost no air or light pollution, the night sky is very clearly visible. Night after night, Yangdol and Dorjay observe the stars and experience an immense sense of awe.
Growing up, Yangdol and Dorjay have been hearing interesting stories about stars from their elders. They have heard how some particular stars in the clear skies helped the caravans passing through Nubra in finding direction in the ancient days. They wonder how far away and how big the stars are. They also enjoy trying to find some patterns among the stars that remind them of familiar objects. Have you ever looked at the stars in the night sky and tried to connect them with imaginary lines, just like dots and lines in a drawing?
🔬 Activity 12.1: Let us draw
- •Fig. 12.2 shows bright stars in one part of the night sky.
- •Look at it carefully and try to imagine a pattern formed by a group of stars.
- •Draw lines to connect the stars and make the pattern.
- •Think of an animal or an object that is similar to the pattern drawn by you. Write its name near your pattern.
- •Repeat the above steps and make some more patterns.
- •Now think of an interesting story about your patterns.
- •Compare your patterns with your friends. Are the patterns same or different? Narrate your story to others and listen to theirs.
12.1 Stars and Constellations
At night, when we look up at the sky, we see many stars. Some stars are bright and others are dim. Stars shine with their own light.
💡 Constellations
Some groups of stars appear to form patterns which are like shapes of familiar things. Long ago, when watching stars in the night sky was a favourite pastime, our ancestors identified these star patterns with animals, things or characters in stories. Many cultures had names for patterns based on their own stories. These imaginary shapes helped them in recognising stars in the sky and in navigation.
In earlier times, groups of stars forming patterns were called constellations. Currently, the regions of sky which include these groups of stars are defined as constellations. The International Astronomical Union (IAU) officially listed 88 constellations in the early 20th century, dividing the entire sky into 88 regions.
In earlier times, groups of stars forming patterns were called constellations. Currently, the regions of sky which include these groups of stars are defined as constellations. The International Astronomical Union (IAU) officially listed 88 constellations in the early 20th century, dividing the entire sky into 88 regions.
🌟 More to know!
Since different cultures denoted the constellation boundaries in different ways, an internationally agreed set of constellation boundaries were defined by the IAU in the early 20th century. 88 constellations were officially listed, thus dividing the entire sky into 88 regions.
💡 Orion, Canis Major and Taurus (Fig. 12.3)
Orion is often represented as a hunter. There are three stars in the middle which represent the belt of the hunter. Some people imagine that Orion, followed by his dog (constellation Canis Major), is battling a bull (constellation Taurus).
Sirius — in the constellation Canis Major — is the brightest star in the night sky.
In Indian astronomy, the term nakṣhatra is used for certain stars or groups: Ārdrā = Betelgeuse (in Orion); Kṛittikā = Pleiades (in Taurus); Rohiṇī = Aldebaran (in Taurus).
Sirius — in the constellation Canis Major — is the brightest star in the night sky.
In Indian astronomy, the term nakṣhatra is used for certain stars or groups: Ārdrā = Betelgeuse (in Orion); Kṛittikā = Pleiades (in Taurus); Rohiṇī = Aldebaran (in Taurus).
💡 Big Dipper, Little Dipper & Pole Star (Fig. 12.4)
Big Dipper: A large ladle-shaped pattern of seven stars. It lies in the constellation Ursa Major. In India it is known as Saptaṛiṣhi.
Little Dipper: A smaller ladle-shaped pattern. It lies in the constellation Ursa Minor.
Pole Star (Polaris / Dhruva tārā): Part of the Little Dipper — appears stationary in the North direction. It helps locate the North direction in the Northern hemisphere. (Not visible from the southern hemisphere.)
Local stories: tribes in Central India view the four rectangular stars of Big Dipper as a "grandmother's cot" with three thieves (other stars) stealing it. Fishermen along Konkan coast imagine the four stars as a boat.
Little Dipper: A smaller ladle-shaped pattern. It lies in the constellation Ursa Minor.
Pole Star (Polaris / Dhruva tārā): Part of the Little Dipper — appears stationary in the North direction. It helps locate the North direction in the Northern hemisphere. (Not visible from the southern hemisphere.)
Local stories: tribes in Central India view the four rectangular stars of Big Dipper as a "grandmother's cot" with three thieves (other stars) stealing it. Fishermen along Konkan coast imagine the four stars as a boat.
12.2 Night Sky Watching
If it is a clear cloudless night, a large number of stars may be visible. In big cities, only a few stars are seen due to light pollution (excessive artificial light at night time), smoke and dust. The night sky is best viewed from open dark areas. Not all stars and constellations are visible from all places on Earth and on all nights in a year. Sky mapping apps (like Sky Map or Stellarium) can help you find when and where a star or constellation is visible from your location.
🌟 Do you know?
Light pollution is growing sharply globally, reducing our ability to enjoy and study objects in the night sky. Some dark sky reserves and parks have been established around the world to control light pollution and preserve dark skies for research.
💡 Preparation for Night Sky Watching
• Under adult guidance, identify a dark open area away from lights, tall buildings and trees.
• Choose the date/time based on what you plan to identify.
• Choose a moonless night with no clouds (particularly for the Pole Star, which is not very bright).
• Carry a sky map app or printed images of the constellations, a magnetic compass, and a notebook.
• After reaching the location, wait about half an hour for your eyes to get adjusted to the darkness. This will help you see the night sky better (Fig. 12.5).
⚠️ Caution: Do not go to a dark open place at night without adults.
• Choose the date/time based on what you plan to identify.
• Choose a moonless night with no clouds (particularly for the Pole Star, which is not very bright).
• Carry a sky map app or printed images of the constellations, a magnetic compass, and a notebook.
• After reaching the location, wait about half an hour for your eyes to get adjusted to the darkness. This will help you see the night sky better (Fig. 12.5).
⚠️ Caution: Do not go to a dark open place at night without adults.
🔬 Activity 12.2: Let us try to locate — Big Dipper & Pole Star
- •Look for the Big Dipper during summer time in the early part of the night, around 9 pm.
- •View the sky above the horizon towards the northern part and identify the Big Dipper.
- •Once you identify the Big Dipper, try to locate the Pole Star: look at the two stars at the end of the Big Dipper's cup and imagine a straight line passing through them towards the north.
- •At about five times the distance between those two stars, the imaginary line will lead to another star which is not very bright — this is the Pole Star.
🔬 Activity 12.3: Let us try to identify — Orion & Sirius
- •In India, Orion is best viewed during December to April after sunset. Look for it during that period.
- •Three bright stars in a short straight line are located around the middle of Orion (the belt of the hunter). Identify these three stars first — this is the easiest way to find Orion.
- •Once you identify Orion, locate the very bright star Sirius: imagine a straight line passing through the three middle stars of Orion and look along this line towards the east. This will lead to Sirius.
- •Which star is closest to us? → Our Sun is the star closest to us.
12.3 Our Solar System
💡 The Sun
The Sun is a star — it is the star closest to us. It is an extremely hot spherical ball of gases that produces heat and light. The Sun is the main source of energy on Earth (Fig. 12.6).
• The Sun is about 100 times bigger than the Earth in diameter.
• The distance of the Sun from Earth is about 150 million km — this is called 1 astronomical unit (au).
• It looks small because it is very far from Earth.
• The nearest star after the Sun is Proxima Centauri, which lies at a distance of about 269,000 au.
During daytime, due to the extreme brightness of the Sun, it is not possible to view other stars.
• The Sun is about 100 times bigger than the Earth in diameter.
• The distance of the Sun from Earth is about 150 million km — this is called 1 astronomical unit (au).
• It looks small because it is very far from Earth.
• The nearest star after the Sun is Proxima Centauri, which lies at a distance of about 269,000 au.
During daytime, due to the extreme brightness of the Sun, it is not possible to view other stars.
💡 Planets & the Solar System
A planet is a large, nearly spherical object that revolves around the Sun. The movement of an object around the Sun is called revolution. The Earth takes nearly one year to complete one revolution.
The eight planets in order of increasing distance from the Sun are:
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune (Fig. 12.7)
Inner four planets (Mercury, Venus, Earth, Mars) — smaller, solid surfaces with rocks.
Outer four planets (Jupiter, Saturn, Uranus, Neptune) — much larger, mostly made of gases ("giant gaseous planets"); have large flat ring-like structures made of dust and rocky material.
Indian names for planets: Budha (Mercury), Śhukra (Venus), Pṛithvī (Earth), Mangala (Mars), Bṛihaspati/Guru (Jupiter), Śhani (Saturn).
Special features:
• Venus = Morning Star / Evening Star (not a star; very bright)
• Mars = Red Planet (reddish iron-rich soil)
• Earth = Blue Planet (surface covered with water, appears blue from space)
• Planets farther from the Sun are generally colder (though atmosphere can trap heat — Venus is hotter than Mercury despite being farther away)
The eight planets in order of increasing distance from the Sun are:
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune (Fig. 12.7)
Inner four planets (Mercury, Venus, Earth, Mars) — smaller, solid surfaces with rocks.
Outer four planets (Jupiter, Saturn, Uranus, Neptune) — much larger, mostly made of gases ("giant gaseous planets"); have large flat ring-like structures made of dust and rocky material.
Indian names for planets: Budha (Mercury), Śhukra (Venus), Pṛithvī (Earth), Mangala (Mars), Bṛihaspati/Guru (Jupiter), Śhani (Saturn).
Special features:
• Venus = Morning Star / Evening Star (not a star; very bright)
• Mars = Red Planet (reddish iron-rich soil)
• Earth = Blue Planet (surface covered with water, appears blue from space)
• Planets farther from the Sun are generally colder (though atmosphere can trap heat — Venus is hotter than Mercury despite being farther away)
🌟 More to know! — Dwarf Planets
Pluto lies farther than Neptune and revolves around the Sun. When discovered, it was called a planet. Later, when similar small objects were found, the IAU in 2006 redefined the requirements. These smaller objects, including Pluto, are now called <strong>dwarf planets</strong>.
🌟 More to know! — Earth's rotation
While revolving around the Sun, the Earth also rotates about its axis. One full rotation takes about 24 hours — called a day. Like Earth, other planets also rotate about their axes while revolving around the Sun.
🔬 Activity 12.4: Let us try to identify — Venus
- •For most of the year, Venus can be located either at dawn or at dusk.
- •When viewing at dawn, look for it near the Eastern direction before sunrise.
- •When viewing at dusk, look for it near the Western direction after sunset.
- •Note: Unlike stars, planets do not appear to twinkle a lot. This helps distinguish planets from stars.
- •To see planets not visible to the naked eye, use binoculars or a telescope (Fig. 12.8).
Natural Satellites
💡 Satellites
Objects that move around planets are commonly called satellites. They are smaller in size than planets. Moons are natural satellites of planets.
• Earth has one Moon
• Mars has two moons
• Jupiter, Saturn, Uranus and Neptune have a large number of moons
• Earth has one Moon
• Mars has two moons
• Jupiter, Saturn, Uranus and Neptune have a large number of moons
💡 The Moon
Earth's natural satellite, the Moon, takes about 27 days to complete one revolution around Earth. It is our nearest neighbour in space.
• The Moon is about a quarter the size of Earth in diameter.
• Distance from Earth: about 3,84,000 km.
• There is hardly any atmosphere on the Moon.
• The Moon's surface has circular bowl-like structures called craters (Fig. 12.9), formed mainly due to the impact of asteroids or rocks from space. Since there is no atmosphere/water/life, these craters stay for a very long time.
• The Moon is about a quarter the size of Earth in diameter.
• Distance from Earth: about 3,84,000 km.
• There is hardly any atmosphere on the Moon.
• The Moon's surface has circular bowl-like structures called craters (Fig. 12.9), formed mainly due to the impact of asteroids or rocks from space. Since there is no atmosphere/water/life, these craters stay for a very long time.
🌟 Do you know? — Chandrayaan Missions
• <strong>Chandrayaan-1</strong> (2008): India's first Moon mission.<br/>• <strong>Chandrayaan-2</strong> (2019): Second mission.<br/>• <strong>Chandrayaan-3</strong> (July 2023): Its Vikram lander carrying the Pragyan rover successfully soft-landed on the Moon on <strong>August 23, 2023</strong>. India became the <strong>first country</strong> in the world to achieve a landing near the Moon's south pole. August 23 is now celebrated as <strong>National Space Day</strong> in India.<br/>• <strong>Chandrayaan-4</strong>: Being planned — aims to bring back soil and rock samples from the Moon.
Asteroids and Comets
💡 Asteroids
The Sun and the planets are nearly spherical in shape. There are many small objects in the Solar System which are rocky and irregular in shape — these are called asteroids. Many asteroids revolve around the Sun in paths lying between those of Mars and Jupiter — this region is called the asteroid belt (Fig. 12.7). Sizes range from 10 m to about 500 km. Occasionally, asteroids pass very close to Earth.
💡 Comets
Sometimes we have visitors from the outer regions of the Solar System — objects with long tails called comets (Fig. 12.10). They are made up of dust, gases, rocks and ice.
As a comet approaches close to the Sun, the frozen material starts evaporating, forming the tail. Comets appear dim as they move away from the Sun.
Many comets revolve around the Sun periodically. Some escape the Solar System; others get broken up or fall into the Sun or planets.
Famous comet: Halley's Comet — appears every 76 years; last appearance was in 1986.
In Sanskrit and other Indian languages, a comet is called Dhūmaketu. Various tribes call it Pucchya-Taro (star with a tail) or Zendya-Taro (star like a flag).
As a comet approaches close to the Sun, the frozen material starts evaporating, forming the tail. Comets appear dim as they move away from the Sun.
Many comets revolve around the Sun periodically. Some escape the Solar System; others get broken up or fall into the Sun or planets.
Famous comet: Halley's Comet — appears every 76 years; last appearance was in 1986.
In Sanskrit and other Indian languages, a comet is called Dhūmaketu. Various tribes call it Pucchya-Taro (star with a tail) or Zendya-Taro (star like a flag).
💡 The Solar System — Summary
The Sun, eight planets, their moons, and many smaller objects including asteroids and comets, together form the Solar System.
The Sun — our star — is the largest and heaviest object in the Solar System. The Sun produces almost all the energy in the Solar System. All other objects shine due to the sunlight they reflect.
The Sun — our star — is the largest and heaviest object in the Solar System. The Sun produces almost all the energy in the Solar System. All other objects shine due to the sunlight they reflect.
12.4 The Milky Way Galaxy
In the moonless night sky, viewed from dark locations away from city lights, one can see an extended faint band of light from near north to south across the sky (Fig. 12.11). This is our home galaxy called the Milky Way Galaxy or Ākāśha Gangā. A galaxy has millions to billions of stars. Our Solar System is part of the Milky Way Galaxy.
12.5 The Universe
There are many galaxies in outer space beyond the Milky Way Galaxy. Scientists study them to understand the stars, galaxies and the universe. We do not know yet if life exists elsewhere in the Universe. The search for life has been directed mostly towards exoplanets — planets discovered revolving around other stars in our galaxy. Till now, scientists have not found any evidence of life, but this search continues.
Keywords
Asteroid▼
Comet▼
Constellation▼
Milky Way Galaxy▼
Moon▼
Planet▼
Revolution▼
Satellite▼
Solar System▼
Stars▼
Sun▼
Draw▼
Explore▼
Identify▼
Observe▼
📝 Summary (Key Points)
- 1The sky is divided into regions called constellations, which include groups of stars that appear to form patterns.
- 2The Pole Star appears stationary in the North direction, which helps in locating the North direction in the Northern hemisphere.
- 3The Sun is a star which produces heat and light.
- 4A planet is a large, nearly spherical object that revolves around the Sun.
- 5The eight planets, in order of their increasing distance from the Sun, are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
- 6The Earth revolves around the Sun in nearly one year.
- 7Objects that move around planets are commonly called satellites.
- 8The Moon is Earth's natural satellite.
- 9The Moon revolves around the Earth in nearly 27 days.
- 10The Sun, eight planets, their moons, and many smaller objects including asteroids and comets, together form the Solar System.
- 11Our Solar System is part of the Milky Way Galaxy.
📚 Let us enhance our learning
Loading your answers...
1
Match the column:
(i) Satellite of Earth → (a) Orion / (b) Venus / (c) Mars / (d) Moon
(ii) Red planet → (a) Orion / (b) Venus / (c) Mars / (d) Moon
(iii) Constellation → (a) Orion / (b) Venus / (c) Mars / (d) Moon
(iv) Planet which is commonly called an evening star → (a) Orion / (b) Venus / (c) Mars / (d) Moon
2
(i) Solve the following riddle: My first alphabet is in MAN but not in CAN / My second alphabet is in ACE and also in FAN / My third alphabet is in RAT and not in CAT / My fourth alphabet is in SUN but not in FUN / I am a planet that moves around the Sun. (ii) Make two similar riddles by yourself.
3
Which of the following is NOT a member of our Solar System? (i) Sirius (ii) Comets (iii) Asteroids (iv) Pluto
4
Which of the following is NOT a planet of the Sun? (i) Jupiter (ii) Pluto (iii) Neptune (iv) Saturn
5
Which is the brighter star, the Pole Star or Sirius?
6
An artist's representation of the Solar System is given in Fig. 12.12. Is the order of the planets correct (Mercury, Earth, Venus, Mars, Jupiter, Uranus, Saturn, Neptune)? If not, write the correct order.
7
A portion of night sky with stars is shown in Fig. 12.13. Look carefully and identify the groups of stars that form the patterns — Big Dipper and Little Dipper. Draw lines to connect the stars and label them. Also identify and label the Pole Star. (Refer to Fig. 12.4 for help.)
8
A portion of the night sky is shown in Fig. 12.14. Draw lines to connect the stars for Orion and label the star Sirius. (Refer to Fig. 12.3.)
9
You can see stars fading away at dawn and appearing at dusk. During the day we do not see the stars. Explain why.
10
During a clear night, try to observe the Big Dipper 3–4 times at an interval of 2 to 3 hours. Also try to locate the Pole Star each time. Does the Big Dipper appear to move? Draw a rough sketch to illustrate this, mentioning the time in each case.
11
Think about the night sky and write a poem or a story on it.
🚀 Learning Further
- Try to find out the names of planets in your local language. Also, find out the stories associated with stars and constellations in your region. Present these stories in a pictorial form.
- If there is a planetarium or a science museum nearby, you can visit it, especially if a night sky observation session is scheduled. You will get to see the Moon, the planets and the stars through a telescope.
- Find out if the increasing light pollution is causing problems for humans, wildlife and the environment. Write an action you would take at the personal level to control light pollution.
- Find out the weather conditions due to which the Indian Institute of Astrophysics (IIA) found Hanle, Ladakh a suitable place to set up an observatory.
- If you enjoy doing embroidery, try to embroider on a dark coloured cloth the constellations that you have seen (Fig. 12.15). Otherwise, depict constellations in multiple other ways using art and craft ideas.
- More to know! — Indian Astronomical Observatory, Hanle: Situated atop the highest peak of the Digpa-rasta-Ri mountain range, renamed Mount Saraswati. Has several telescopes including the Himalayan Chandra Telescope (named after Nobel laureate Subrahmanyan Chandrasekhar). The Hanle Dark Sky Reserve (HDSR) was notified in December 2022 — open to the public year-round. Local people are trained as Astronomy Ambassadors to promote astro-tourism.
🌟 It is not the end, my friend!
This might be the last page of this book, but it is certainly not the end of our "Curiosity". Science is a never-ending adventure, with new discoveries coming up all the time. Keep observing the world around you, keep asking questions, and do not be afraid to experiment. Remember, even the most groundbreaking discoveries often begin with a simple "Why?". There are countless questions waiting to be answered, and countless answers waiting to be questioned. You, my young scientist, can find them out. So, go forth and explore!
