Question

[Typed answers please]

1. Write a paragraph explaining why Seasons occur on the Earth.

2. In a short paragraph, explain how Newton’s Law of Gravity depends on mass and distance. Don’t just write the equation; explain what the equation means and give some simple numerical examples. 3. What is mass, and how does it differ from weight? Write a paragraph.

4. List Kepler's Laws of Planetary Motion and briefly explain what each means.

5. In a paragraph, describe at least two of the telescopic observations made by Galileo which supported the Sun-centric Copernican model of the Solar System.

6. What is retrograde motion of planets and how does the Copernican model of the solar system explain this apparent motion? Write a paragraph.

7. What is parallax, and why did the apparent absence of stellar parallax lead the Greeks to believe that the Earth must be stationary? Write a parargraph.

8. Write a paragraph describing the two ‘main powers’ of telescopes. Explain why it is useful for astronomers to build bigger and bigger telescopes.

9. What are emission and absorption line spectra? Write a paragraph explaining what they are and why they are important to astronomy.

10. Write a paragraph explaining why astronomers sometimes need to put telescopes in space in order to do their science.

Answer 1

(1)

Why Seasons occur on the Earth -

We all know that earth revolves around the sun.

Earth's obliquity or tilt in it's axis is main reason behind changing seasons on earth.

When earth points towards the sun, temperature of that side of earth increases and it's summer for that part. When earth

points away from the sun, temperature reduces and it is winter for that part of earth.

Autumn and spring also occur at different tilt angles.

(2)

According to Newton's Law of gravity,

every particles in universe attracts each other with a gravitational force that is directly proportional to mass of those

particles and inversely proportional to the distance b/w them.

Gravitational force, Fg = Gm1*m2 / d^2

Here G is gravitational constant.

m1 and m2 are masses of two objects and d is distance b/w them.

Ex: if two objects 5 kg and 7 kg are placed at 10 m distance,

Fg = G*5*7 / 10^2

Fg = 0.35G

When distance b/w them reduces to 5 m,

Fg = G*5*7 / 5^2 = 1.4G

so, we can say that when distance b/w objects reduces, gravitational force increases b/w them.

(3)

Mass (m) is a property of a matter. It is amount of matter which does not change according to place or location.

It is measured in grams or kgs.

On the other hand, Weight is a vector quantity that measures effect of gravity on mass.

Weight = m*g

here, m = mass of object , g = gravitational acceleration

It varies according to place and location.

eg; weight of a object is different on earth and moon.