Hello my dear students! Welcome to today's science class. I am so happy to see you all here, ready to learn about something truly wonderful and vast. Today, we are going to explore Chapter 12 of your Science textbook, and the title of this chapter is "Beyond Earth" — but as you will see, it is really about Stars and the Solar System. Isn't that exciting? We are going to travel far beyond our planet and discover amazing things about the universe that surrounds us. Are you ready? Let us begin our journey!
Imagine you are in a beautiful place called Nubra in Ladakh. It is a region in the mountains of northern India, and it is one of the most stunning places you can imagine. There lives an eleven-year-old girl named Yangdol and her twin brother Dorjay. They live in one of the villages of Nubra, and they absolutely love their surroundings — the majestic mountain peaks, the glaciers, but their favourite thing of all is the night sky. When the night comes in Nubra, the entire sky gets lit up with thousands and thousands of stars. The weather in Nubra is almost always clear, with hardly any clouds. And because there is almost no air pollution and no light pollution from cities, the night sky is so clearly visible that it takes your breath away. Every night, Yangdol and Dorjay look up at the stars and feel a deep sense of wonder and awe.
Now, students, have you ever looked at the stars in the night sky? Have you ever tried to connect them with imaginary lines, like dots and lines in a drawing? This is exactly what we are going to learn about today. Let us start by understanding what stars are and how we can recognize different patterns in the sky.
## Activity 12.1: Let Us Draw
Now, students, I want you to look at Figure 12.2 in your textbook. It shows some bright stars in one part of the night sky. I want you to look at it carefully and try to imagine a pattern formed by a group of stars. Can you see some stars that seem to form a shape? Now, draw lines to connect the stars and make a pattern. Think of an animal or an object that looks similar to the pattern you have drawn. Write its name near your pattern.
Now, try to make some more patterns. Think of interesting stories about your patterns. After you have drawn your patterns, compare them with your friends' patterns. Are they the same or different? You will notice that everyone's patterns, names, and stories are different. Is it not fun? This is exactly what our ancestors did thousands of years ago. They looked at the night sky and saw patterns in the stars. And that, students, is how the study of stars and constellations began.
## 12.1 Stars and Constellations
Now, let us understand what stars actually are. At night, when we look up at the sky, we see many stars. Some stars are bright and some are dim. But here is an important thing to remember — stars shine with their own light. They are like giant balls of hot gas that produce their own light and heat. Our Sun is also a star, but it is much closer to us than the other stars, so it looks very bright and big. The other stars are so far away that they look like tiny points of light.
Now, what are constellations? Let me explain this to you. Some groups of stars appear to form patterns that look like familiar things — like animals, objects, or characters from stories. Long ago, when our ancestors used to watch the stars in the night sky as a favourite pastime, they identified these star patterns with animals, things, or characters in stories. Many different cultures from around the world had their own names for these patterns based on their own stories and beliefs. These imaginary shapes helped them in recognizing stars in the sky.
Recognizing stars and their patterns was a very useful skill for navigation in the olden times. Before modern technology was invented, before people had smartphones or even magnetic compasses, sailors and travelers used the stars to find their directions at sea or on land. Even today, if you are ever in an emergency and you do not have any technology, you can still use the stars to find your way. It is a backup method that has been used for thousands of years.
In earlier times, groups of stars forming patterns were called constellations. But now, students, the term constellation has a more specific meaning. Currently, the term constellation refers to defined regions of the sky that often include these patterns of stars. However, because the patterns of stars are often the most noticeable feature, we still commonly use the term constellation for these groups of stars.
Now, here is something interesting. Different cultures from around the world denoted the constellation boundaries in different ways. So, to make things consistent, an internationally agreed set of constellation boundaries were defined by the International Astronomical Union, which we call the IAU, in the early twentieth century. They officially listed 88 constellations, and this divided the entire sky into 88 regions. These regions of the sky are now defined as constellations.
Let us look at some constellations. In Figure 12.3, you can see some constellations and stars. The stars are joined by imaginary lines, which are drawn only for easy identification. You do not actually see these lines in the sky. One very famous constellation is Orion, which is often represented as a hunter. There are three stars in the middle of Orion, which represent the belt of the hunter. Some people imagine that the hunter Orion, followed by his dog which is another constellation called Canis Major, is battling a bull which is the constellation Taurus. Canis Major contains a star called Sirius, which is the brightest star in the entire night sky.
Now, students, in Indian astronomy, we have our own special terms. We use the term nakshatra to denote either a certain star or a group of stars. For example, Ārdrā is a star called Betelgeuse in the Orion constellation, and Kṛttikā is a group of stars called Pleiades in the Taurus constellation. Aldebaran, a star in the constellation Taurus, is known as Rohiṇī in India. These are names that have been used in Indian astronomy for thousands of years.
Now, let me tell you about two very important star patterns — the Big Dipper and the Little Dipper. These are shown in Figure 12.4. The Big Dipper is part of a larger constellation called Ursa Major, which means the Great Bear. The Little Dipper is part of the constellation Ursa Minor, which means the Little Bear. The Pole Star, also called Polaris, is part of the Little Dipper. In India, we call the Big Dipper "Saptarishi" because it looks like seven sages or wise men. And the Pole Star is known as "Dhruva tārā," which means the fixed star. The Pole Star is very important because it appears nearly stationary in the North direction. This helps us to locate the North direction in the Northern hemisphere. If you ever get lost at night in the Northern hemisphere, finding the Pole Star can help you find your way.
Now, students, I want to tell you something fascinating. Different communities in India have their own stories about the stars. For example, the four stars in the Big Dipper that approximately form a rectangle are viewed by tribes in Central India as "grandmother's cot" with three other stars being "thieves" trying to steal it. Fishermen along the Konkan coast imagine these four stars as a boat, with the last three stars as the neck of the boat. Isn't it wonderful how different people see different things in the same stars?
Now, let me pause here and recap what we have learned so far. We learned that stars are objects that shine with their own light. We learned that groups of stars form patterns called constellations, which have been used for navigation for thousands of years. We learned about the Big Dipper, the Little Dipper, and the Pole Star. And we learned that in India, we have our own traditional names for stars and constellations, like Saptarishi and Dhruva tārā. Make sure you remember these points, as they are very important.
## 12.2 Night Sky Watching
Now, students, let us learn about how to watch the night sky. If it is a clear, cloudless night, you can see a large number of stars in the sky. But if you live in a big city, you may find that the sky is rarely clear and only a few stars are visible. This is because of something called light pollution, smoke, and dust. Light pollution is the presence of excessive artificial light at night time. In villages or areas where there is less light pollution, you can see many more stars. Also, if your house is surrounded by tall buildings and trees, they may block your view. So, the best place to watch the night sky is from an open dark area, away from city lights.
Light pollution is growing sharply all over the world. This is reducing our ability to enjoy and study objects in the night sky. That is why some dark sky reserves and parks have been established around the world. In these places, light pollution is controlled to preserve dark skies for research. There are organizations that are working to educate people about reducing light pollution.
Now, here is something important to remember. Not all stars and constellations are visible from all places on Earth and on all nights of the year. For example, the Pole Star is not visible from the southern hemisphere of Earth. To identify a star or a constellation, you need to know what it looks like and where to look for it in the night sky. To get familiar with the pattern of a constellation, you may use images from your textbook or other resources.
There are also some very helpful apps that you can use on your mobile phone. For example, Sky Map is a very handy app for identification of stars, constellations, and planets. Stellarium is another such app. The computer version of Stellarium is free to download and has many features. These apps can show you what the sky looks like on any particular date and time from your location.
Now, let us talk about how to prepare for night sky watching. First, under the guidance of adults, you need to identify a dark open area for watching the night sky. This should be away from lights, tall buildings, and trees. Second, with the help of an app, choose the date and time based upon what you plan to identify in the night sky. Third, choose a night where neither the Moon nor the clouds are visible, particularly if you want to identify the Pole Star, which is not very bright. Fourth, it may be useful to have access to a mobile app with a map of the sky, or print out images of the constellations you plan to view. You may also carry a magnetic compass to find directions and a notebook to note or draw your observations. Fifth, on the particular day and time selected, go to the identified place with an adult. Sixth, after reaching there, wait for about half an hour for your eyes to get adjusted to the darkness. This will help you see the night sky better.
Remember, students, a very important caution — do not go to a dark open place at night time without adults accompanying you. Safety first!
Now, let us do Activity 12.2. In this activity, we will try to locate the Big Dipper and the Pole Star. First, look for the Big Dipper during summer time in the early part of the night, say around 9 PM. View the sky towards the northern part of the sky and identify the Big Dipper. Once you identify the Big Dipper, try to locate the Pole Star. Look at the two stars present at the end of the Big Dipper's cup and imagine a straight line passing through these towards the north. At about five times the distance between these two stars, the imaginary line will lead to another star which is not very bright. This star is the Pole Star. You may also locate the bright constellation Orion and the star Sirius in the night sky.
Now, let us do Activity 12.3. In this activity, we will try to identify the constellation Orion and the star Sirius. In India, Orion is best viewed during the months of December to April after sunset. So, look for it during that period. Three bright stars in a short straight line are located around the middle of Orion, which is imagined to be the belt of a hunter. Identify these three stars first, as this is the easiest way to find Orion. Once you identify Orion, it is easy to locate the very bright star Sirius, which is located close to Orion. 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.
Now, students, let me ask you a question that is in your textbook. Which star is closest to us? The answer is that among the stars we can see, the Sun is closest to us. But wait, the Sun is a star too! So, the Sun is the closest star to us. The next closest star after the Sun is Proxima Centauri, which is about 269,000 astronomical units away. That is an enormous distance!
Now, let me recap what we learned in this section. We learned about light pollution and why it is important to watch the night sky from dark areas. We learned how to prepare for night sky watching, including waiting for our eyes to adjust to the darkness. We learned how to locate the Big Dipper and the Pole Star. And we learned how to identify Orion and Sirius. These are all practical skills that you can use when you go out to watch the night sky. Remember these points, and try to apply them when you get a chance.
## 12.3 Our Solar System
Now, students, we are going to learn about something truly amazing — our Solar System. But first, let us start with the Sun, which is the most important object in 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. The Sun gives out a huge amount of energy, and that is why it glows so brightly. The Sun produces heat and light, and it is the main source of energy on the Earth.
How big is the Sun? It is about 100 times bigger than the Earth in diameter. And still, it looks so small because it is very far from the Earth. The distance of the Sun from the Earth is about 150 million kilometers. A useful unit for expressing distances within the solar system is "astronomical unit" which is approximately the distance between the Sun and the Earth. So, we can say that the Sun is about 1 astronomical unit away from the Earth.
Now, students, here is something very interesting. The Sun, being the brightest object and the source of light and heat on Earth, was elevated in most ancient civilizations to the status of a deity. In India, the Sun is worshipped as Sūrya. The heat provided by the Sun keeps the Earth at a temperature that makes life possible. Sunlight is essential for plants to grow, which provide food and oxygen to animals, including humans. The Sun is responsible for climate, seasons, weather, water cycle, winds — all of which are important for sustaining life on the Earth.
Now, here is a question that might have puzzled you. Our Sun is also a star. So, how is it that the Sun appears big and lights up the sky while the other stars look like bright dots in the night sky and are not even visible during the day time? The answer is that the Sun is much closer to us than the other stars, hence it appears much bigger than the stars. As the stars, other than the Sun, are much farther away, they appear like points, even though some of those stars are much bigger than our Sun. During daytime, due to the extreme brightness of the Sun, it is not possible to view other stars from Earth. That is why we only see the stars at night, when the Sun is below the horizon.
Now, are stars the only objects in the sky? Or are there more objects which we may not have noticed? There are many more objects in the sky. Our Earth, along with some of these objects, and the Sun together form our Solar System. Most of these objects move around the Sun. The movement of an object around the Sun is called revolution.
Now, students, let me explain what planets are.
### Planets
A planet is a large, nearly spherical object that revolves around the Sun. Our Earth is a planet because it revolves around the Sun. The Earth takes nearly one year to complete one revolution around the Sun. Like the Earth, there are other planets that revolve around the Sun.
The eight planets, in order of their increasing distance from the Sun, are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Let me say that again so you can remember: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
The inner four planets nearest to the Sun — Mercury, Venus, Earth, and Mars — are smaller in size. They have solid surfaces with rocks on them. The four outermost planets — Jupiter, Saturn, Uranus, and Neptune — are much larger compared to the Earth, and are mostly made of gas and ice. These giant planets have large flat ring-like structures around them which are made of dust particles and rocky material. You might have seen pictures of Saturn with its beautiful rings.
Now, let me tell you some interesting facts about the planets. Venus is usually seen shining brightly at dawn and dusk, and is commonly called the Morning Star or the Evening Star, even though it is not a star. It is actually a planet. Mars is called the Red Planet because it appears red. This is because the soil on Mars is reddish in color. A large portion of the Earth's surface is covered with water, and thus it appears blue from space. Due to this, the Earth is also called the Blue Planet.
Planets get most of their energy from the Sun. So, the farther they are, the colder they are in general. The presence of an atmosphere on a planet can trap heat, which can significantly change the temperature of a planet. That is why Venus, for example, is hotter than Mercury, although it is farther from the Sun. This might seem strange, but it is because Venus has a thick atmosphere that traps heat.
Now, here is something interesting. From ancient times, various names have been used across India for the planets visible to the naked eye. For example, Budha is Mercury, Śhukra is Venus, Prithvi is Earth, Mangala is Mars, Brihaspati or Guru is Jupiter, and Śhani is Saturn. These are Sanskrit names that have been used for thousands of years.
Now, can we identify a planet the way we identified the constellations? Among the planets, it is easiest to identify Venus, which is very bright. After the Sun and the Moon, Venus is the brightest object in the sky. Mercury, Mars, Jupiter, and Saturn can also be seen with the naked eye. They are so far away that they look like shining dots, just like stars. So, how can we distinguish between planets and the stars? Unlike planets, the stars appear to twinkle a lot. This is because of the Earth's atmosphere. The light from stars has to pass through the Earth's atmosphere, which is always moving, and this makes the stars appear to twinkle. Planets, being closer, appear as small disks rather than points, and they twinkle less.
Now, let me ask you a question from your textbook. How can we see the planets which are not visible to the naked eye? While many of the objects in the sky can be seen with our naked eyes directly, we can see them brighter and larger using a pair of binoculars or an instrument called a telescope. A telescope also helps us view many dim objects not visible by our naked eyes directly. You may get an opportunity to view the sky through a telescope whenever a night sky watching event is organized in your region. Many Higher Education Institutions conduct night sky watching activities for school students. There are many Amateur Astronomy Clubs all over the country which organize sky watching events periodically. Museums and Planetariums also organize similar events.
Now, let me tell you about something else. We know that planets move around the Sun. Are there any objects that move around planets? Yes, there are! Objects that move around planets are commonly called satellites. They are smaller in size than planets. Moons are natural satellites of planets. The Earth has one Moon, while Mars has two moons. Jupiter, Saturn, Uranus, and Neptune have a large number of moons.
### The Moon
Now, let us talk about Earth's natural satellite, the Moon. The Moon takes about 27 days to complete one revolution around the Earth. It is our nearest neighbor in space. Unlike on the Earth, there is hardly any atmosphere on the Moon. How big is the Moon compared to the Earth? The Moon is about a quarter the size of the Earth in diameter. The Moon's surface shows circular bowl-like structures called craters. Most of these craters have been formed due to the impact of asteroids or rocks from space hitting the Moon's surface. Since there is no atmosphere, water, or life on the Moon, these features stay on the Moon's surface for a very long time.
Although the Moon is very far, humans have sent spacecrafts to explore and understand more about the Moon. India has also launched three Chandrayaan missions to study the Moon, and a further mission is being planned. To improve our understanding of the Moon, India's first mission to the Moon, Chandrayaan-1, was launched in 2008, and the second mission, Chandrayaan-2, in 2019. The third mission, Chandrayaan-3, was launched in July 2023, and its Vikram lander carrying the Pragyan rover successfully soft-landed on the Moon on 23 August 2023. With this mission, India became the first country in the world to achieve a landing near the little-explored Moon's south pole. To mark this success, the Government of India declared 23 August to be celebrated as "National Space Day" in India. A fourth mission, Chandrayaan-4, is being planned, which aims to bring back soil and rock samples from the Moon.
The Moon is about 384,000 kilometers away from the Earth. That is quite far, but it is the closest object to us in space.
Now, students, let me ask you something. In general, any object that moves around a much larger object can also be called a satellite. For example, Earth can be considered a satellite of the Sun because it moves around the Sun.
### Asteroids
Now, let us learn about asteroids. The Sun and the planets are nearly spherical in shape. But there are many small objects in the Solar System which are rocky and irregular in shape. These are called asteroids. Many of these asteroids revolve around the Sun in paths that lie between those of Mars and Jupiter. This region is called the asteroid belt. Occasionally, some asteroids pass very close to the Earth. The sizes of asteroids range from about 10 meters to about 500 kilometers.
### Comets
Now, here is something really interesting. Sometimes we have visitors from the outer regions of the Solar System! These objects with long tails are called comets. They are made up of dust, gases, rocks, and ice. As a comet approaches close to the Sun, the frozen material in it starts evaporating. This evaporating material forms the tail of the comet. Comets appear dim as they move away from the Sun, and then it is not possible to see them with the naked eye.
Many comets have been found that revolve around the Sun. These comets approach close to the Sun periodically. However, there are a few comets that escape and move out of the Solar System. A few other comets get broken up, or fall into the Sun or other planets when they approach them.
One famous comet is Halley's Comet, which appears every 76 years. Its last appearance was in 1986. In Sanskrit and a few other Indian languages, a comet is called Dhūmaketu, which means "the one with a smoky flag." Various tribes in India also call it Pucchya-Taro, which means "star with a tail," or Zendya-Taro, which means "star like a flag." In many cultures, comets have been feared, and it was earlier believed that comets bring bad luck. However, thanks to scientists, we now know that these are just icy-rocky visitors making a trip close to the Sun!
Now, students, let me summarize what we have learned about the Solar System. 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 the heaviest object in the Solar System. The Sun produces almost all the energy in the Solar System. All other objects in our Solar System shine due to the sunlight that they reflect from their surfaces.
Now, let me recap what we learned in this section. We learned that the Sun is a star that produces heat and light. We learned that planets are objects that revolve around the Sun. We learned the names of the eight planets in order: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. We learned about natural satellites, especially our Moon. We learned about asteroids, which are rocky objects between Mars and Jupiter. And we learned about comets, which are icy visitors from the outer Solar System. Make sure you remember all these points, as they are very important.
## 12.4 The Milky Way Galaxy
Now, students, we are going to learn about something even bigger than the Solar System. 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. This is our home galaxy, called the Milky Way Galaxy, or Ākāsha Gangā in Sanskrit. A galaxy has millions to billions of stars. Our Solar System is part of the Milky Way Galaxy. The Milky Way Galaxy contains about 100 to 400 billion stars, including our Sun. When you look at that faint band of light across the sky, you are actually looking at millions of stars all bunched together. It looks like a milky path, which is why it is called the Milky Way.
## 12.5 The Universe
Now, what is beyond the Milky Way Galaxy? There are many galaxies in the outer space beyond the Milky Way Galaxy. Scientists study them to understand the stars, galaxies, and the Universe. The Universe is everything — all the galaxies, all the stars, all the planets, and everything else that exists. It is so vast that it is almost impossible to imagine.
Now, here is a question that has fascinated humans for a very long time. Is there life anywhere else in the Universe? We do not know yet if life exists elsewhere in the Universe. The search for life has been directed mostly towards exoplanets — the planets discovered revolving around other stars in our galaxy. Till now, scientists have not found any evidence of life, but this search is on and continuing. Perhaps one day, you or someone you know might make this amazing discovery!
Now, students, let me recap what we learned in the last few sections. We learned about the Milky Way Galaxy, which is our home galaxy. We learned that there are many other galaxies beyond our own. And we learned that we are still searching for life elsewhere in the Universe. These are big ideas, but they are important to understand.
Now, let us move on to the exercises in your textbook. I am going to solve each question for you, step by step, just like we would do in class.
## Let Us Enhance Our Learning
### Question 1
Match the column:
Column I | Column II ---|--- (i) Satellite of Earth | (a) Orion (ii) Red planet | (b) Venus (iii) Constellation | (c) Mars (iv) Planet which is commonly called an evening star | (d) Moon
Now, let me solve this for you. The satellite of Earth is the Moon, so (i) matches with (d). The Red planet is Mars, because it appears red due to its reddish soil, so (ii) matches with (c). A constellation is a group of stars that form a pattern, and Orion is a famous constellation, so (iii) matches with (a). And the planet commonly called the Evening Star is Venus, because it shines brightly at dawn and dusk, so (iv) matches with (b).
So the answers are: (i) — (d), (ii) — (c), (iii) — (a), (iv) — (b).
### Question 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."
Now, let me solve this riddle step by step. We need to find a four-letter word that is a planet name.
First alphabet: in MAN but not in CAN. The letters in MAN are M, A, N. The letters in CAN are C, A, N. The letter that is in MAN but not in CAN is M.
Second alphabet: in ACE and also in FAN. The letters in ACE are A, C, E. The letters in FAN are F, A, N. The common letters are A. So the second alphabet is A.
Third alphabet: in RAT but not in CAT. The letters in RAT are R, A, T. The letters in CAT are C, A, T. The letter that is in RAT but not in CAT is R.
Fourth alphabet: in SUN but not in FUN. The letters in SUN are S, U, N. The letters in FUN are F, U, N. The letter that is in SUN but not in FUN is S.
So the letters are M, A, R, S. Put them together, and we get MARS. And Mars is indeed a planet that moves around the Sun! So the answer is Mars.
(ii) Make two similar riddles by yourself.
Now, students, I want you to try making your own riddles. Here is an example:
Riddle 1: "My first alphabet is in BUT and not in PUT. My second alphabet is in EAR and also in TEA. My third alphabet is in MAN and not in PAN. I am a planet that moves around the Sun."
Let me solve it: First letter: B (in BUT, not in PUT). Second letter: A (in EAR and TEA). Third letter: M (in MAN, not in PAN). That gives us BAM, which is not a planet. Let me try again.
Let me make one for VENUS: "My first alphabet is in VAN but not in PAN. My second alphabet is in TEN and also in MEN. My third alphabet is in USE and not in DUE. My fourth alphabet is in SUN but not in FUN."
First: V (in VAN, not in PAN). Second: E (in TEN and MEN). Third: N (in USE, not in DUE). Fourth: U (in SUN, not in FUN). That gives VENUS. Yes!
Now try one for MERCURY: "My first alphabet is in MET but not in BET. My second alphabet is in EAR and also in PEA. My third alphabet is in CAR but not in BAR. My fourth alphabet is in RUN but not in RAN. My fifth alphabet is in YOU but not in COU."
First: M (in MET, not in BET). Second: E (in EAR and PEA). Third: C (in CAR, not in BAR). Fourth: R (in RUN, not in RAN). Fifth: U (in YOU, not in COU). That gives MERCUR. We need Y. Let me adjust.
Actually, let me make it simpler. Try making riddles for planets with names that have unique letters. You can use the same pattern as the example in your textbook.
### Question 3
Which of the following is not a member of our Solar System? (i) Sirius (ii) Comets (iii) Asteroids (iv) Pluto
Now, let me solve this. Sirius is a star, which is not part of our Solar System. It is part of the Milky Way Galaxy, but it is not part of our Solar System. Comets and asteroids are indeed members of our Solar System. And Pluto, although reclassified as a dwarf planet, is still part of our Solar System. So the answer is (i) Sirius.
### Question 4
Which of the following is not a planet of the Sun? (i) Jupiter (ii) Pluto (iii) Neptune (iv) Saturn
Now, let me solve this. Jupiter, Neptune, and Saturn are all planets of the Sun. Pluto was considered a planet until 2006, when it was reclassified as a dwarf planet by the International Astronomical Union. So technically, Pluto is not a planet of the Sun according to the current definition. The answer is (ii) Pluto.
### Question 5
Which is the brighter star, the Pole Star or Sirius?
Now, this is a straightforward question. Sirius is the brightest star in the night sky. The Pole Star is not very bright at all. In fact, in the activity we did earlier, we noted that the Pole Star is "not very bright." So Sirius is the brighter star.
### Question 6
An artist's representation of the Solar System is given in Fig. 12.12. Is the order of the planets correct? If not, write the correct order in the boxes in the figure.
Now, students, I cannot see the figure in your textbook, but I can tell you the correct order of the planets from the Sun. The correct order is: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Remember the mnemonic: My Very Educated Mother Just Served Us Noodles. The first letters stand for Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. So if the order in your figure is different from this, then it is incorrect.
### Question 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 — the Big Dipper and the Little Dipper. Draw lines to connect the stars for these patterns and label them. Also, identify and label the Pole Star. You may refer to Fig. 12.4 for help.
Now, students, I cannot see the figure, but I can describe what you need to do. The Big Dipper consists of seven stars. Four stars form the "cup" or "bowl," and three stars form the "handle." The Little Dipper also consists of seven stars. It has a "cup" at one end and a "handle" extending outward. The Pole Star is at the end of the Little Dipper's handle. You need to look at the figure in your textbook, identify these patterns, draw lines to connect the stars, and label them. This is an activity that you need to do with the figure in your book.
### Question 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. You may refer to Fig. 12.3.
Again, students, I cannot see the figure, but I can tell you what to look for. Orion is a constellation that looks like a hunter. It has three stars in a row that form the hunter's belt. There are four stars that form the hunter's shoulders and feet. Sirius is a very bright star located near Orion. You need to look at the figure in your textbook, identify Orion, draw lines to connect the stars, and label Sirius. This is an activity that you need to do with the figure in your book.
### Question 9
From Earth, you can see stars fading away at dawn and appearing at dusk. During the day we do not see the stars. Explain why.
Now, let me explain this. The stars are always there in the sky, even during the day. However, we cannot see them during the day because of the Sun. The Sun is so bright that its light overwhelms the faint light from the stars. It is like trying to see a small candle flame next to a powerful spotlight — you simply cannot see the dim light because the bright light is too overwhelming.
At dawn, as the Sun rises, its light gradually becomes brighter and overwhelms the starlight, so the stars fade away. At dusk, as the Sun sets, its light gradually becomes dimmer, and the stars become visible. So, the reason we do not see stars during the day is that the Sun's bright light makes them invisible to us.
### Question 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.
Now, students, this is an activity that you need to do practically. The answer is that yes, the Big Dipper does appear to move across the sky during the night. This is because the Earth is rotating on its axis. As the Earth rotates, the stars appear to move across the sky. The Big Dipper, like all other stars, rises in the east and sets in the west, just like the Sun. However, the Pole Star appears nearly stationary because it is located very close to the direction of the Earth's axis. So, if you observe the Big Dipper at different times during the night, you will see that it has moved. But the Pole Star will remain in roughly the same position. You need to go out on a clear night and observe this for yourself, then draw a sketch showing the position of the Big Dipper at different times.
### Question 11
Think about the night sky and write a poem or a story on it.
Now, students, this is a creative activity. I want you to use your imagination and write a poem or a story about the night sky. You can write about the stars, the Moon, the planets, or anything else related to the night sky. Let me give you an example of a simple poem:
"Twinkle, twinkle, little star, How I wonder what you are! Up above the world so high, Like a diamond in the sky."
This is a famous poem by Jane Taylor. But I want you to write your own original poem or story. Let your imagination run wild!
Now, students, we have completed all the exercises in the "Let us enhance our learning" section. Let me now move on to the "Learning further" section, which has some additional activities.
## Learning Further
The first activity says: 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.
Now, students, I want you to research the names of planets in your local language or regional language. For example, in Hindi, we say Budha for Mercury, Shukra for Venus, Prithvi for Earth, Mangala for Mars, Brihaspati or Guru for Jupiter, and Shani for Saturn. You can also ask your grandparents or elders about stories associated with stars and constellations in your region. There might be interesting local traditions and stories that have been passed down through generations. Then, you can present these stories in a pictorial form — maybe as a drawing, a painting, or a collage.
The second activity says: If there is a planetarium or a science museum nearby, then you can visit it, especially if a night sky observation session is scheduled by them. You will get to see the Moon, the planets, and the stars through a telescope. If you visit the planetarium during daytime, you can also see their models, pictures, and sky shows.
This is a wonderful activity. If you have the opportunity to visit a planetarium, definitely go for it. You will be able to see the Moon, planets, and stars through a telescope, which is an amazing experience. Planetariums also have shows that can teach you a lot about the night sky.
The third activity says: Find out if the increasing light pollution is causing problems for humans, wildlife, and the environment. Write an action that you would take at the personal level to control light pollution.
Now, students, light pollution is a serious issue. It affects humans by preventing us from seeing the beautiful night sky. It affects wildlife because many animals rely on natural light cycles for their behavior. And it affects the environment because excessive artificial light wastes energy. At the personal level, you can take several actions to control light pollution. For example, you can use downward-facing lights instead of upward-facing lights, turn off unnecessary outdoor lights, use motion sensors for outdoor lighting, and spread awareness about light pollution in your community.
The fourth activity says: 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.
Now, students, Hanle in Ladakh is an excellent place for an observatory because it has very clear skies, low humidity, minimal light pollution, and stable atmospheric conditions. These are ideal for astronomical observations. The Indian Institute of Astrophysics set up an observatory there because the weather conditions are perfect for studying the night sky.
The fifth activity says: If you enjoy doing embroidery, try to embroider on a dark colored cloth the constellations that you have seen. Otherwise, you may use your creativity and depict constellations in multiple other ways using various art and craft ideas.
This is a fun creative activity. You can use embroidery, painting, drawing, or any other art form to depict the constellations. This will help you remember the patterns of the stars.
Now, there is also some additional information in your textbook about the Indian Astronomical Observatory at Hanle. It is situated atop the highest peak of the Digpa-ratsa-Ri mountain range in Hanle. This peak has been renamed Mount Saraswati. It has several telescopes. One of them is called the Himalayan Chandra Telescope, which has been named after the Nobel Prize winning scientist Subrahmanyan Chandrasekhar. It is an observatory at one of the highest locations in the world.
The area surrounding this observatory was notified as the Hanle Dark Sky Reserve in December 2022. The reserve is open to the public throughout the year. Local people have been provided with small telescopes and are trained to be Astronomy Ambassadors for visitors by the Indian Institute of Astrophysics. It is expected to promote astro-tourism in the region.
Now, students, we have covered the entire chapter. Let me summarize everything we have learned in this lesson.
## Summary
In this chapter, we learned about the night sky and our place in the universe. We started with the story of Yangdol and Dorjay from Nubra, who loved watching the stars. We learned that stars are objects that shine with their own light, and that groups of stars form patterns called constellations. We learned that constellations have been used for navigation for thousands of years. We learned about the Big Dipper, the Little Dipper, and the Pole Star, and how to locate them in the night sky. We learned that in India, we have our own traditional names for stars and constellations, like Saptarishi and Dhruva tārā.
We learned about night sky watching, and how light pollution affects our ability to see stars. We learned how to prepare for night sky watching, including finding a dark location and waiting for our eyes to adjust to the darkness.
We learned about our Solar System. We learned that the Sun is a star, and it is the closest star to us. We learned that planets are objects that revolve around the Sun. We learned the names of the eight planets in order: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. We learned about the inner planets, which are smaller and have solid surfaces, and the outer planets, which are larger and made of gas and ice. We learned about natural satellites, especially our Moon. We learned about asteroids, which are rocky objects between Mars and Jupiter. And we learned about comets, which are icy visitors from the outer Solar System.
We learned about the Milky Way Galaxy, which is our home galaxy. We learned that there are many other galaxies beyond our own. And we learned that we are still searching for life elsewhere in the universe.
We also solved all the exercises in the textbook, including matching columns, solving riddles, identifying which objects are not part of our Solar System, and explaining why stars are not visible during the day.
Students, this is the end of our lesson, but it is not the end of your journey into space. The universe is vast and full of mysteries waiting to be discovered. Keep looking up at the night sky, keep asking questions, and keep exploring. Who knows? Maybe one of you will become a great astronomer and make amazing discoveries about the universe!
Thank you for listening to this lesson. I hope you enjoyed learning about the stars and the Solar System as much as I enjoyed teaching you. Until next time, keep curious and keep exploring!