PSC Elementary Science note The Universe

PSC Elementary Science Note: The Universe

The Universe: Now, you are going to introduce to a new chapter-The Universe. This chapter has no similarity to the previous chapters. The subject matter of this chapter is different from others. You will know many unknown facts of The Universe. I think some students will face difficulty when they start reading this chapter. But don’t worry. Most of the students start to memorise without understanding. After some time, they fail to remember some little things. For every topic, we need to read with a deep sense of understanding. It helps us to give answer properly. Now the students have to face creative questions. If they understand the topic clearly, they can answer any question properly. It proves a student’s creative skill. And at the same time, it discourages memorised answers. It helps to get a clear conception and to achieve a standard mark. It’s my opinions that go through this chapter properly and remind some points properly. Moreover, I will help you by giving you easy solution.

At a Glance

  1. Size of Universe
  2. Motions of Earth
  3. Day and Night
  4. Sunrise and Sunset
  5. Summer and Winter
  6. Motion of the Moon
  7. The Moon in Rotation

For clear conception, I usually enlarge the length of short answered questions. But in the PSC exam, you give the answer in one or two lines for short questions. You get 1 mark for each question. So you don’t need to give answers broadly.

Short Answered Questions (Main Text)
1. What are two motions of the Earth?
Ans: Revolution: The path that earth and other planets move around the Sun is called orbit. The orbital motion of the Earth around the Sun is called Revolution. It takes 365 days and 6 hours for the Earth to complete one trip around the Sun.
Rotation: While revolving the Sun, Earth also spins or rotates on its axis like a spinning top. The spinning motion of the Earth on its axis is called Earth’s rotation. It takes 23 hours and 56 minutes for the Earth to complete one full rotation on its axis, which is measured as one day.

PSC-elementary-science-note-the--universe-motions-of-the-earth

Figure: Seasonal Changes

2. What causes day and night?
Ans: The Earth’s rotation causes day and night.
Day and Night
The Earth is spinning on its axis once every 24 hours. That is why the sun rises in the morning and sets in the evening every day. One side of the Earth is facing the Sun, whereas the other side of the Earth is not facing the Sun. The part of the Earth that is facing the Sun has daytime. On the other hand, the part of the Earth that is facing away from the Sun has night.

PSC Elementary Science note the Universe Day and Night
Figure: Day and Night

3. Why do the phases of the Moon take place?
Ans: The Moon seems big or small, and round or half round-shaped on some nights. The changing shapes of the bright part of the Moon that we see are called the phases of the Moon.
The Moon does not give off its own light. It reflects the Sun’s light. Half of the moon is always lighted by the Sun. And this part looks bright. The other half looks dark. When the Moon orbits around the Sun, the lighted part of the Moon looks different in different times. These changes cause the phases of the Moon.
Figure

4. What is the difference between planet and satellite?
Ans: Planet: A planet is an object that revolves around Sun. Like Earth.
Satellite: A satellite is an object that revolves around a planet. Like Moon.

5. Why temperature rises in the summer?
Ans: In summer, the sunlight shines more directly on the northern half of the Earth giving more energy, and the Sun appears to rise higher in the sky. This causes the temperatures to rise and the period of daytime to be longer. So temperature rises in the summer.
Figure

Descriptive Questions (Main Text)

1. Explain the causes of seasons.
Ans: We have six seasons such as Summer, Rainy season, Autumn, late Autumn, Winter and Spring in a year.
The tilt of the Earth’s axis and its orbit around the Sun causes Seasons. As the Earth revolves around the Sun, different parts of the Earth tilt toward or away from the Sun.
Summer
When the northern hemisphere tilts toward the Sun, it is Sun, it is summer there. In summer, the sunlight shines more directly on the northern half of the Earth giving more energy, and the Sun appears to rise higher in the sky. This causes the temperatures to rise and the period of daytime to be longer. Opposite season occurs in the southern hemisphere and it is winter there.

Winter
When the Northern Hemisphere tilts away from the Sun, it is winter there. In winter, sunlight hits that part of the Earth less directly, and the Sun appears to rise lower in the sky. The temperature is lower, and the period of daytime is shorter but the period of night gets longer.

2. The sun does not move, but it seems to move from east to west across the sky. Explain why.
Ans: The Sun seems rising in the east in the morning, and then sets in the west as the day ends. This is because the Earth is spinning on its axis from west to east. As Earth turns, the Sun appears to move from east to west across the sky.

3. When the northern half of the Earth tilts toward the Sun, what happens to the height of the Sun and length of day and night?
Ans: When the Northern Hemisphere tilts away from the Sun, it is winter there. In winter, sunlight hits that part of the Earth less directly, and the Sun appears to rise lower in the Sky. The temperature is lower, and the period of daytime is shorter but the period of night gets longer.

4. How are the solar system, the Milky Way Galaxy, and the Universe related?
Ans: The Universe is a vast thing. Countless stars, Sun, Moon, Milky Way Galaxy, and Planets etc all are the members of The Universe. The solar system is located in the Milky Way Galaxy. And The Milky Way Galaxy is in The Universe. So it is said easily that solar system, the Milky Way Galaxy and The Universe are related. Milky Way is one of the galaxies in the Universe. According to Sir Eddington, on an average a galaxy has ten thousand corers of stars. The Universe is still expanding. No one knows for sure about the size of the Universe. However, we can get an impression how big the Universe is from different scientific research on Universe. So the solar system, the Milky Way Galaxy, and the Universe are related.

5. Look at the pictures below. The both of the pictures were taken at the same time and same space, but they look different. Why does it happen?
Ans: Picture
The both of the pictures were taken at the same time and same space but in different season. So they look different. The first picture was taken in June that means in summer season. The second picture was taken in December that means in winter season.
In summer, the sunlight shines more directly on the northern half of the Earth giving more energy, and the Sun appears to rise higher in the sky. This causes the temperatures to rise and the period of daytime to be longer. So the first picture was taken in 5 pm in June looks bright.
In winter, sunlight hits that part of the Earth less directly, and the Sun appears to rise lower in the sky. The temperature is lower, and the period of daytime is shorter but the period of night gets longer. So the second picture looks dark in the comparison of the first picture. The reason behind it is in winter season, the night begins early.

More Questions
1. How does a telescope help us?
Ans: A telescope makes far away objects seem larger. If we use a telescope, we can see these objects more clearly. It helps us see farther into space.

2. Why do scientists use telescope?
Ans: Scientists use telescope to research on planets, stars and galaxy.

3. What is the distance from the Moon to the Earth?
Ans: A distance from the Moon to the Earth is 384,400 km.

4. What is the motion of light? Or, What does it mean by light takes about 1.3 Second to travel from the Moon to the Earth?.
Ans: Light can travel at approximately 300,000 km a second. So, light takes about 1.3 second to travel from the Moon to the Earth.

5. What is the distance from the sun to Earth?
Ans: A distance from the Sun to the Earth is about 150,000,000 km.

6. What do we understand that we always see the sunlight that is emitted from the Sun about 8 minutes ago?
Ans: Light takes about 8 minutes to travel from the Sun to the Earth. This means that we always see the sunlight that is emitted from the Sun about 8 minutes ago.

7. Describe the distance among Sun, Earth and Moon.
Ans: A distance from the Sun to the Earth is about 150,000,000 km. And a distance from the Moon to the Earth is 384,400 km.
Figure

8. What would happen if we were able to travel as fast as light?
Ans: If we were able to travel as fast as light, it would take 1, 30,000 years to go across the Milky Way galaxy.

9. What is Astronomy?
Ans: Astronomy is the study of the Universe such as stars, planets, and space. Scientists use different technologies such as telescope to study the Universe.

10. Who invented an improved telescope?
Ans: Galileo invented an improved telescope that allowed him to see far into space. Using the telescope, he proved that the planets actually revolved around the Sun.

11. Why are scientists using telescopes now?
Ans: Scientists are now using space telescopes and are building a space station to observe the Universe.

12. What is the Earth?
Ans: The Earth is one of the planets in the solar system. The Earth moves in a path around the Sun like other planets.

13. What is an Axis?
Ans: An Axis is an imaginary line through the centre of an object through. Earth’s axis goes through the North and South poles. Earth’s axis is tilted at some degree.

14. Describe motion of the Earth?
Ans: The Moon is the only satellite of the Earth. A satellite is an object that revolves around a planet. The Moon rotates on its axis once every about 28 days and it also moves around the Earth once every about 28 days.

15. Describe full Moon and new Moon. Or, The Moon in Rotation.
Ans: The Moon does not give off its own light. It reflects the Sun’s light. Half of the moon is always lighted by the Sun. And this part looks bright. The other half looks dark. When the Moon orbits around the Sun, the lighted part of the Moon looks different in different times. These changes cause the phases of the Moon. We can only see the bright side of the Moon. When we can see full of the side lighted, this is a full Moon. When we can’t see any of the bright side, this is called a new Moon.
Figure

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