Stars and the Solar System

This chapter takes you on a tour of the night sky. You will learn why the Moon shows phases, from new moon through crescent, half moon and gibbous to full moon and back, in about 29.5 days, because we see different portions of its sunlit half as it revolves around the Earth. You will learn that the Moon has no atmosphere or water, and that we always see the same side of it. Stars, including our Sun, are huge balls of hot gas that emit their own light, and their distances are measured in light years. You will identify constellations such as Ursa Major (Saptarishi), Orion and Cassiopeia, and locate the Pole Star. The solar system consists of the Sun and the eight planets, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune, along with their moons, asteroids, comets and meteors. You will compare the features of each planet and learn about natural and artificial satellites, such as Aryabhata, INSAT and Chandrayaan.

Detailed Worksheet: Stars and the Solar System Section A - Definitions (10 marks) 1. What are the phases of the Moon? Why does the Moon appear to change its shape? (2 marks) 2. Define a light year. Is it a unit of time or distance? (2 marks) 3. What is a constellation? Name two constellations visible from India. (2 marks) 4. What are asteroids? Where are they found in the solar system? (2 marks) 5. Distinguish between a meteor and a meteorite. (2 marks) Section B - Calculations and Applications (15 marks) 6. Light travels about 3,00,000 km in one second. Calculate the distance travelled by light in one year (take 1 year = 365 days) and express it in kilometres. (3 marks) 7. The Sun is about 15,00,00,000 km (150 million km) from the Earth. Calculate how long sunlight takes to reach the Earth, in seconds and in minutes, taking the speed of light as 3,00,000 km/s. (3 marks) 8. Alpha Centauri is about 4.3 light years away. If a star exploded today at that distance, after how many years would we see it? How many kilometres away is it? (Take 1 light year = 9.46 x 10^12 km.) (3 marks) 9. Halley's comet appears after about 76 years. It was last seen in 1986. In which year is it expected next? If a person saw it in 1910, in which years could he have seen it before and after? (3 marks) 10. The full moon was seen on 1 March. On about which date will the next full moon occur? On about which date will the new moon occur between them? (Take the lunar cycle as about 30 days.) (3 marks) Section C - Diagrams (10 marks) 11. Draw a labelled diagram showing the Sun and the eight planets in their correct order. Mark the asteroid belt. (4 marks) 12. Draw the pattern of stars of Ursa Major and show how it can be used to locate the Pole Star. (3 marks) 13. Draw a labelled diagram showing the positions of the Moon in its orbit around the Earth on new moon day and full moon day, with the Sun's rays. (3 marks) Section D - Analysis and Higher-order Thinking (15 marks) 14. Explain why the Pole Star does not appear to move while other stars seem to move from east to west. Why can the Pole Star not be seen from the southern hemisphere? (5 marks) 15. Compare the planets Venus, Jupiter, Saturn and Uranus by giving one special feature of each. Why is Venus called the morning or evening star although it is not a star? (5 marks) 16. What are artificial satellites? How are they different from natural satellites? Give four uses of artificial satellites, naming one Indian satellite or mission for each use. (5 marks) Instructions: Time allowed 2 hours. Attempt all sections. Show all steps in calculations and write large numbers in powers of 10 where needed.