Class 6 Science Chapter 12 Notes Beyond Earth
This chapter introduces the wonders of outer space. It covers the complete solar system including Sun, planets, satellites, asteroids, etc. Also, in this chapter, we will study human efforts to explore space and space missions and the possibility of life beyond Earth.
Stars and Constellations
Many stars can be seen in the sky at night. Stars can be bright or dim. They shine with their light. Some groups of stars appear to form patterns that are like shapes of familiar things, animals or characters of stories. Before the arrival of modern technology or even before, the invention of the magnetic compass, recognizing stars and their patterns helped people 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 regions of the sky, which include these groups of stars, are defined as constellations. Some constellations are shown in the Figure given below. The stars are joined by imaginary lines for easy identification. An internationally agreed set of constellation boundaries was defined by the International Astronomical Union (IAU) in the early 20th century. The entire sky is divided into 88 regions. These regions of the sky are now officially defined as constellations.
→ The constellation Orion is often represented as a hunter. There are three stars in the middle, which represent the belt of the hunter.
→ It is believed that the hunter Orion is followed by his dog (constellation Canis Major), which is battling a bull (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 the Orion constellation.
→ Krittika is a group of stars called Pleiades in the Taurus constellation.
→ Aldebaran, known as Rohini is a star in the constellation Taurus.
→ The Big Dipper and the Little Dipper are two distinct patterns of stars. The Pole Star or Polaris is a part of the Little Dipper.
→ The Big Dipper lies in the constellation Ursa Major while the Little Dipper lies in the constellation Ursa Minor.
→ In India, the Big Dipper is known as Saptarishi, and the Pole star is known as Dhruva Tara as shown in Figure.
→ The Pole star appears stationary in the North direction, which helps to locate the North direction in the Northern hemisphere. The Pole star is not visible from the southern hemisphere of Earth.
Night Sky Watching
Light pollution, dust, and smoke are reducing the ability to enjoy and study objects in the night sky. The presence of excessive artificial light at night time is referred to as light pollution. The night sky is best viewed from open dark areas at places, where there is less light and air pollution. But not all stars and constellations are visible from all places on Earth and on all nights in a year.
To find out a star or a constellation
Sky mapping apps help to find out when and in which portion of the sky a star or a constellation will be visible from your location. These apps can be downloaded on mobile phones. Sky Map is a very handy app for the identification of stars, constellations, and planets from mobile phones. Stellarium is another such app and its computer version is free for download and has many features.
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.
- 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. Also, carry a magnetic compass to find directions and a notebook to note observations.
- On the particular day and time selected, go to the identified place with an adult, where the night sky watching is to be done.
- 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.
- You may easily identify the Big Dipper, the Pole Star, a bright constellation, and the star Sirius in the night sky.
Some dark sky reserves and parks have been established around the world. Light pollution in the reserves is controlled to preserve dark skies for research. Many Higher Education Institutions all over the country along with museums and planetariums conduct night sky watching activity.
Our Solar System
The Sun
Sun, the closest star to us, produces heat and light and is the main source of energy on the Earth. It is about 100 times bigger than the Earth in diameter. The distance of the Sun from the Earth is about 150 million km. ‘Astronomical unit’ (AU) is a useful unit for expressing distances within the solar system which is approximately the distance between the Sun and the Earth. Proxima Centauri is another star nearest to us after the Sun, which lies at a distance of about 269000 AU.
There are many more objects in the sky moving around the> Sun. The movement of an object around the Sun is called a revolution. The Sun, eight planets, their moons, and many smaller objects including asteroids and comets, together form the solar system. In most ancient civilizations, Suo was given the status of a deity. In India, the Sun is worshipped as Surya. The Sun is responsible for the growth of plants, maintaining climate, seasons, weather, water cycle,’ and winds all of which are important for sustaining life on the Earth.
Planets
Planets are large spherical objects that revolve around the Sun. Our planet Earth takes nearly one year to complete one revolution. The Earth also rotates about its axis while revolving around the Sun. For one full rotation, the Earth takes about 24 hours which is called a day. Like the Earth, other planets 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.
→ 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.
→ Venus is commonly called the Morning Star or the Evening Star, even though it is not a star. It is because it shines bright at dawn and dusk.
→ Mars is called the Red Planet because the soil on Mars is reddish. Hence, it appears red.
→ Earth is called the blue planet as a large portion of the Earth’s surface is covered with water and thus, it appears blue from the space.
→ The four outermost planets Jupiter, Saturn, Uranus, and Neptune are mostly made up of gases. These giant gaseous planets have large flat ring-like structures around them which are made of dust particles and rocky material.
→ Some planets can be seen with the naked eyes but they look like shining dots, just like stars. To distinguish between the two, do remember that stars appear to twinkle a lot.
→ A telescope helps us to view many dim objects which are not visible to our naked eyes directly.
Different names of the planets which are visible to the naked eye are listed in the following table.
| Actual Name | Another Name |
| Mercury | Budha |
| Venus | Shukra |
| Earth | Prithvi |
| Mars | Mangala |
| Jupiter | Brihaspati or Guru |
| Saturn | Shani |
Natural Satellites
Objects that move around the planets are called satellites. 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. Earth can be considered a satellite of the Sun. In general, any object that moves around a much larger object can also be called a satellite.
The Moon
Earth’s natural satellite, the Moon, takes about 27 days to complete one revolution around the Earth and it is about 3,84,000 km away from the Earth.There is no atmosphere on the Moon. The Moon is about a quarter the size of the Earth. The Moon’s surface shows circular bowl-like structures called craters. (Scan the QR code to see). Most of these craters have been formed due to the impact of asteroids or rocks from space hitting the Moon’s surface. India has launched three Chandrayaan missions to study the Moon, and a further mission is being planned.
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 Pragyanrover successfully landed on the Moon on August 23, 2023. With this mission, India became the first country in the world to achieve a landing near the Moon’s South Pole. To mark this success, the Government of India declared August 23 to be celebrated as National Space Day in India.
Asteroids
Asteroids are rocky irregularly shaped objects in the solar system. 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. The sizes of asteroids are from 10 m to about 500 km.
Comets
Visitors from the outer regions of the solar system having 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. 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 Dhumaketu. Various tribes in India also call it Pucchya-Taro (star with a tail) or Zendya-Taro (star like a flag).
The Milky-Way Galaxy and the Universe
All the stars we see in the night, sky including our solar system are a part of the Milky Way Galaxy or Akasha Ganga. Our galaxy is called the Milky Way because it appears as a milky band of light in the sky when you see it in a really dark area. There are many galaxies in the outer space beyond the Milky Way Galaxy which constitutes the whole universe.
Indian Astronomical Observatory Hanle, is situated at the highest peak of Digpa-rasta-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 Chandrashekhar. The area surrounding this observatory was notified as the Hanle Dark Sky Reserve (HDSR) in December 2022.
→ Constellations: A region in which a group of stars appear to form patterns are called constellations.
→ Sun: Sun is the closest star to us that produces heat and light and is the main source of energy on the Earth.
→ Revolution: The movement of an object around the Sun is called revolution.
→ Planets: Planets are large spherical objects that revolve around the Sun.
→ Satellite: Objects that move around the planets are called satellites.
→ Moon: Moons are the natural satellites of planets.
→ Asteroid: Asteroids are rocky irregular-shaped objects in the solar system revolving around the Sun between the paths of Mars and Jupiter.
→ Comet: Visitors from the outer regions of the solar system having long tails are called comets.
→ Solar System: The Sun, eight planets, their moons and many smaller objects including asteroids and comets, together form the solar system.
→ Milky-Way Galaxy is an isolated collection of all the stars we see in the night sky including our solar system.