Welcome dear students! Today we are going to learn about Beyond Earth from Class 6 Science. Let us begin our journey to the stars. Imagine a beautiful region in Ladakh called Nubra. An eleven-year-old girl named 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. 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. [CHECKPOINT]
Growing up, they have heard interesting stories about stars from their elders. They heard how some particular stars helped caravans passing through Nubra find direction in ancient days. They wonder how far away and how big the stars are. They also enjoy finding patterns among the stars that remind them of familiar objects. Have you ever looked at the stars and tried to connect them with imaginary lines, just like dots and lines in a drawing? Let us do Activity twelve point one. Let us draw. Look at a part of the night sky showing bright stars. 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 steps and make some more patterns. Now think of an interesting story about your patterns. Compare your patterns with your friends. Are they the same or different? Narrate your story to others and listen to theirs. Do you notice that everyone's patterns, names, and stories are different? Is it not fun? [CHECKPOINT]
Now let us move on to section twelve point one, Stars and Constellations. At night, when we look up at the sky, we see many stars. Some are bright and others are dim. Stars shine with their own light. Some groups of stars appear to form patterns which look like shapes of familiar things. Long ago, when watching stars 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. Recognising stars and their patterns was a useful skill for navigation in the olden times. Before modern technology or the magnetic compass, it helped sailors and travellers find directions at sea or on land. It is still used in emergencies as a backup method. 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. However, since the patterns of stars are often the most prominent, the term constellation is still commonly used for these groups. Since different cultures denoted the constellation boundaries differently, an internationally agreed set of boundaries was defined by the International Astronomical Union in the early twentieth century. Eighty-eight constellations were officially listed, dividing the entire sky into eighty-eight regions. [CHECKPOINT]
Some constellations are shown in diagrams where stars are joined by imaginary lines for easy identification. The constellation 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 the hunter Orion, followed by his dog, the constellation Canis Major, is battling a bull, the constellation Taurus. Canis Major contains a star called Sirius, which is the brightest star in the night sky. In Indian astronomy, the term nakshatra is used to denote either a certain star or a group of stars, such as Ardra, a star called Betelgeuse in Orion, and Krittika, a group of stars called Pleiades in Taurus. Aldebaran, a star in Taurus, is known as Rohini. Two distinct patterns of stars, the Big Dipper and the Little Dipper, are also shown. The Pole Star or Polaris, part of the Little Dipper, is shown as well. The Pole Star appears stationary in the North direction, which helps to locate North in the Northern hemisphere. The Big Dipper lies in the constellation Ursa Major while the Little Dipper lies in Ursa Minor. In India, the Big Dipper is known as Saptarishi, and the Pole Star is known as Dhruva tara. Many forest dwelling communities or tribes of India have their own stories about them. For example, tribes in Central India view the four stars of the Big Dipper forming a rectangle as the grandmother's cot, with the other three stars as thieves stealing it. Fishermen along the Konkan coast imagine the four stars as a boat, with the last three stars as the neck of the boat. [CHECKPOINT]
Let us move to section twelve point two, Night Sky Watching. If it is a clear cloudless night, a large number of stars may be visible. In a big city, the sky is rarely clear and only a few stars are seen due to light pollution, smoke, and dust. The presence of excessive artificial light at night time is referred to as light pollution. In villages or areas with less light pollution, more stars can be seen. Tall buildings and trees may also block your view. The night sky is best viewed from open dark areas. 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 to control light pollution and preserve dark skies for research. Not all stars and constellations are visible from all places on Earth and on all nights in a year. For example, the Pole Star is not visible from the southern hemisphere. To identify a star or constellation, you need to know how it looks and where to look. To find out when and where a star will be visible from your location, you may use sky mapping apps on a mobile phone or other online resources. [CHECKPOINT]
Sky Map is a very handy app for identification of stars, constellations and planets from mobile phones. Stellarium is another such app. The computer version of Stellarium is free for download and has many features. Now, preparation for night sky watching. Under the guidance of adults, identify a dark open area for night sky watching. This should be away from lights, tall buildings, and trees. Choose the date and time based upon what you plan to identify. Choose a moonless night with no clouds, particularly for the Pole Star which is not very bright. It may be useful to have access to a mobile app with a sky map, 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. On the selected day and time, go to the identified place with an adult. After reaching there, wait for about half an hour for your eyes to get adjusted to the darkness. This will help you to see the night sky better. Caution: Do not go to a dark open place at night time without adults accompanying you. You may easily identify the Big Dipper and the Pole Star in the night sky. [CHECKPOINT]
Let us do Activity twelve point two. Let us try to locate. Look for the Big Dipper during summer time in the early part of the night, say, around nine p m. View the sky above the horizon towards the northern part and identify the Big Dipper. Once you identify it, 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 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. Now Activity twelve point three. Let us try to identify. 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, 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. [CHECKPOINT]
Let us move to section twelve point three, Our Solar System. 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 is the main source of energy on the Earth. How big is the Sun? It is about one hundred times bigger than the Earth in diameter. It looks small because it is very far. The distance of the Sun from the Earth is about one hundred fifty million kilometres. A useful unit for expressing distances within the solar system is astronomical unit, abbreviated as au, which is approximately the distance between the Sun and the Earth. The Sun was elevated in most ancient civilizations to the status of a deity. In India, the Sun is worshipped as Surya. 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, and winds, all important for sustaining life on Earth. [CHECKPOINT]
Our Sun is also a star. So why does it appear big while other stars look like bright dots and are not visible during the day? The Sun is much closer to us than other stars, hence it appears much bigger. Other stars are much farther away, so they appear like points, even though some are much bigger than our Sun. During daytime, due to the extreme brightness of the Sun, it is not possible to view other stars. The star nearest to us after the Sun is Proxima Centauri, which lies at a distance of about 269000 au. This means its distance is about 269000 times our distance to the Sun. Are stars the only objects in the sky? There are many more objects. 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. A planet is a large, nearly spherical object that revolves around the Sun. Our Earth is a planet as it revolves around the Sun, taking nearly one year to complete one revolution. Like Earth, other planets also revolve around the Sun. While revolving, the Earth is also rotating about its axis. For one full rotation, the Earth takes about twenty-four hours, which is called a day. Other planets also rotate about their axes while revolving. [CHECKPOINT]
The eight planets, in order of their increasing distance from the Sun, are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. The inner four planets nearest to the Sun are smaller in size. They have solid surfaces with rocks on them. From ancient times, various names have been used across India for the planets visible to the naked eye. For example, Budha for Mercury, Shukra for Venus, Prithvi for Earth, Mangala for Mars, Brihaspati or Guru for Jupiter, and Shani for Saturn. 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. Mars is called the Red Planet because its soil is reddish in colour. A large portion of Earth's surface is covered with water, making it appear blue from space, so it is also called the Blue Planet. The four outermost planets, Jupiter, Saturn, Uranus, and Neptune, are much larger compared to Earth, and are mostly made of gases. These giant gaseous planets have large flat ring-like structures around them made of dust particles and rocky material. 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 can trap heat, significantly changing a planet's temperature. That is why Venus is hotter than Mercury, although it is farther from the Sun. There is another object called Pluto that lies farther than Neptune. It is smaller than Earth's Moon. When discovered, it was called a planet. But later, the International Astronomical Union in 2006 redefined the requirements. As per this definition, smaller objects like Pluto are now called dwarf planets. [CHECKPOINT]
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 look like shining dots, just like stars. So how can we distinguish between planets and stars? Unlike planets, stars appear to twinkle a lot. Let us do Activity twelve point four. Let us try to identify. 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. While many objects can be seen with our naked eyes, we can see them brighter and larger using binoculars or a telescope. A telescope also helps view many dim objects not visible directly. You may get an opportunity to view the sky through a telescope during organised night sky watching events. Many Higher Education Institutions, Amateur Astronomy Clubs, Museums, and Planetariums conduct these activities for students and the public. [CHECKPOINT]
Now let us learn about Natural Satellites. Objects that move around planets are commonly called satellites. They are smaller than planets. Moons are natural satellites of planets. Earth has one Moon, Mars has two, and Jupiter, Saturn, Uranus, and Neptune have a large number. In general, any object that moves around a much larger object can be called a satellite. For example, Earth is a satellite of the Sun. The Moon is about 3,84,000 km away from Earth. It takes about twenty-seven days to complete one revolution around Earth. It is our nearest neighbour in space. Unlike Earth, there is hardly any atmosphere on the Moon. The Moon is about a quarter the size of Earth in diameter. Its surface shows circular bowl-like structures called craters. Most craters were formed by 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 for a very long time. Humans have sent spacecraft to explore the Moon. India launched Chandrayaan one in 2008, Chandrayaan two in 2019, and Chandrayaan three in July 2023. Its Vikram lander carrying the Pragyan rover successfully soft-landed on the Moon on 23 August 2023. India became the first country to land near the Moon's south pole. The Government declared 23 August as National Space Day. A fourth mission, Chandrayaan four, is planned to bring back soil and rock samples. [CHECKPOINT]
Let us learn about Asteroids. The Sun and planets are nearly spherical. There are many small objects in the Solar System which are rocky and irregular in shape. These are called asteroids. Many revolve around the Sun in paths between Mars and Jupiter. This region is called the asteroid belt. Occasionally, asteroids pass very close to Earth. Their sizes range from 10 m to about 500 km. Now, Comets. Sometimes we have visitors from the outer regions of the Solar System! These objects with long tails are called comets. They are made of dust, gases, rocks, and ice. As a comet approaches the Sun, frozen material evaporates, forming the tail. Comets appear dim as they move away and cannot be seen with the naked eye. Many comets revolve around the Sun periodically. Some escape the Solar System, while others break up or fall into the Sun or planets. The Sun, eight planets, their moons, asteroids, and comets together form the Solar System. One famous comet is Halley's Comet, which appears every 76 years. Its last appearance was in 1986. The Sun is the largest and heaviest object, producing almost all energy in the Solar System. Other objects shine by reflecting sunlight. In Sanskrit, a comet is called Dhūmaketu. Tribes call it Pucchya-Taro or Zendya-Taro. In many cultures, comets were feared, but we now know they are just icy-rocky visitors. [CHECKPOINT]
Let us move to section twelve point four, The Milky Way Galaxy. In a moonless night sky, viewed from dark locations, one can see an extended faint band of light across the sky. This is our home galaxy, the Milky Way Galaxy or Ākāsha Gangā. A galaxy has millions to billions of stars. Our Solar System is part of it. Section twelve point five covers The Universe. There are many galaxies beyond the Milky Way. Scientists study them to understand stars, galaxies, and the universe. We do not know yet if life exists elsewhere. The search focuses on exoplanets revolving around other stars. No evidence of life has been found yet, but the search continues. More to know: The Indian Astronomical Observatory at Hanle, Ladakh, is situated at one of the highest locations in the world. The area was notified as the Hanle Dark Sky Reserve in December 2022. It promotes astro-tourism and is open to the public. [CHECKPOINT]
Now, let us solve the exercise questions. Question one: Match the columns. Satellite of Earth matches with Moon. Red planet matches with Mars. Constellation matches with Orion. Planet commonly called an evening star matches with Venus. Question two: Solve the riddle. My first letter is in MAN but not in CAN. That is M. Second is in ACE and FAN. That is A. Third is in RAT but not CAT. That is R. Fourth is in SUN but not FUN. That is S. I am a planet that moves around the Sun. The answer is MARS. You are asked to make two similar riddles yourself. Question three: Which is not a member of our Solar System? Options: Sirius, Comets, Asteroids, Pluto. Answer: Sirius, because it is a star. Question four: Which is not a planet of the Sun? Options: Jupiter, Pluto, Neptune, Saturn. Answer: Pluto, reclassified as a dwarf planet. [CHECKPOINT]
Question five: Which is brighter, the Pole Star or Sirius? Answer: Sirius. Question six: Is the order of planets in the figure correct? The correct order from the Sun is Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Question seven: Identify and draw lines for the Big Dipper and Little Dipper, and label the Pole Star. Connect the seven stars of the Big Dipper into a cup and handle. Connect the Little Dipper's stars, noting the Pole Star is at the end of its handle. Question eight: Draw lines for Orion and label Sirius. Connect the stars to form the hunter, focusing on the three belt stars. Extend a line east from the belt to find and label Sirius. Question nine: Why do we not see stars during the day? Answer: The extreme brightness of the Sun outshines the faint light from distant stars. Question ten: Observe the Big Dipper three to four times at two to three hour intervals. Does it appear to move? Yes, it appears to move across the sky due to Earth's rotation, seeming to rotate around the stationary Pole Star. Draw rough sketches showing its shifting position. Question eleven: Write a poem or story about the night sky. [CHECKPOINT]
Learning further: Try to find the names of planets in your local language and stories associated with stars in your region. Present them pictorially. Visit a planetarium or science museum to see models and sky shows. Find out how light pollution affects humans and wildlife, and write a personal action to control it. Learn why the Indian Institute of Astrophysics chose Hanle for an observatory. If you enjoy embroidery, try embroidering constellations on dark cloth, or use other art ideas to depict them. It is not the end, my friend! This is just the beginning of your scientific curiosity. Keep observing, asking questions, and experimenting. Thank you for listening! Keep revising and practicing. Goodbye! [CHAPTER_COMPLETE]