NCERT Book Class 6 Science Beyond Earth PDF Download

Chapter 12: Beyond Earth

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.

[Figure 12.1: The beauty of night sky from a very dark location in Ladakh, India]

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 the patterns drawn by your friends. Are the patterns same or different?
• Narrate your story to others and listen to their stories. Do you notice that everyone's patterns, names and stories are different? Is it not fun?

[Figure 12.2: A part of the night sky]

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. 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 of our ancestors, they 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 the arrival of modern technology or even before the invention of the magnetic compass, it helped people, particularly sailors and travellers, in finding 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 term constellation refers to defined regions of the sky that often include these patterns of stars. However, as the patterns of stars are often the most noticeable feature, the term constellation is still commonly used for these groups of stars.

Teacher's Note

A constellation has two meanings: the original one (a group of stars forming a pattern) and the modern one (a region of the sky defined by the International Astronomical Union). When the book or your exam uses the word "constellation," check the context to understand which meaning is intended. Usually, when talking about stories and patterns, it refers to the star groups.

More to know!

Since different cultures denoted the constellation boundaries in different ways, an internationally agreed set of constellation boundaries were defined by the International Astronomical Union (IAU) in the early twentieth century. 88 constellations were officially listed, thus, dividing the entire sky into 88 regions. These regions of sky are now defined as constellations.

Some constellations are shown in Fig. 12.3. The stars are joined by imaginary lines, drawn 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 (constellation Canis Major), is battling a bull (constellation Taurus). Canis Major contains a star

Teacher's Note

When you learn about constellations like Orion, Canis Major, or Taurus, remember that the imaginary lines connecting the stars are drawn by us - they are not physically there in space. Different cultures drew different lines through the same stars, which is why the same group of stars could represent a hunter in one culture and a different object in another. The lines are just a tool to help us recognize and remember star patterns.

Key Points

• Stars are objects in the night sky that produce their own light. Some appear bright and others appear dim.
• A constellation is a group of stars that forms a recognizable pattern, named after animals, objects, or characters based on cultural stories.
• Before modern technology, constellations helped sailors and travellers find directions on land and at sea.
• The International Astronomical Union officially recognized 88 constellations, which divide the entire sky into 88 regions.
• Stars in a constellation are connected by imaginary lines to help us identify and remember the patterns, but these lines are not real.

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