GCSE Physics- Astronomy

What is the definition of a satellite?

An object that orbits a SECOND, BIGGER object

What are the two types of satellite?

Artificial (manmade) or natural

Describe the orbits of moons

Almost circular / slightly elliptical

Describe the orbits of artificial satellites

Circular orbits

Where are asteroids found?

asteroid belt

Describe the orbits of comets?

highly elliptical

Describe the orbits of planets

Slightly elliptical / almost circular

An object in a circular orbit/motion is at a constant speed is ______________ _________________

Constantly accelerating

What is the gravity to a central point force called?

CENTRIPETAL FORCE

Draw a picture representation of centripetal force of a planet orbiting the sun

Insert pic :/

Explain how centripetal force works against instantaneous velocity

- The gravity is always towards the centre of circle

- the object keeps accelerating towards the centre but due to instantaneous velocity which is at 90° to the acceleration, the object keeps travelling in a circle

Formula for weight in astronomy

W = m x g

Weight = mass x gravitational field strength

The closer you get to an object in space the _____________ the ____________________ __________ is

Stronger the gravitational force is

The stronger the gravitions force is the _____________ the _____________________ ______________ needed to remain in orbit

Larger the instantaneous velocity (so need to go faster)

For an object in a stable orbit, if the speed changes...

The radius must change too

(Indirect proportion ⬆️⬇️)

If speed of an object increases

Radius decreases ⬆️⬇️

⭐️⭐️Exam Question⭐️⭐️

If the distance between the Earth and the Moon was smaller how would the orbital speed of the moon compare to its current orbital speed? (3 marks)

(1) orbital speed would increase

(1) a larger instantaneous velocity is needed to balance out the force of the Earth on the moon

(1) because the closer the moon is to the Earth, the greater the gravitational force on the Moon

⭐️⭐️Exam Question⭐️⭐️

Describe the orbits of

a) planets. b) moons c) comets. (3 marks)

a) almost circular around Sun

b) almost circular around planets

c) highly elliptical around Sun

Describe orbits of planets

Almost circular /slightly elliptical

Gravitational field strength depends on objects' .....

Mass

Weight depends on...

Gravitational field strength of the object it's on

Explain how and why the weight of any body and the value of g differ between different bodies in space

Their gravitational field strength is different due to their mass

(E.g. Earth = 9.8, moon = 1.6)

Describe and explain geocentric model of solar system. What is it? Why did it come about? When did people believe in it?

(1) Sun, moon and planets orbit the Earth in perfect circles

(1) came because people didn't have telescopes

(1) time period = Greeks until 1500s

Describe and explain the heliocentric model of the solar system. What is it?

(1) Sun at the centre of the solar system

(1) planets orbits around the sun in perfect circles

What did Galileo discover?

The moons of Jupiter

How did Galileo prove that the geocentric model is wrong?

He saw some 'stars' around Jupiter that never moved away- this meant that not everything orbited the Earth (Geocentric model)

What does the current model show?

The planets in our solar system orbit the sun

But the orbits are elliptical not circular

What is a current change to the universe that will go on forever?

It is always expanding

Steady State Theory

"The Universe has always existed as it is now and it always will"

What is the Steady State Theory based on?

1) The idea that THE UNIVERSE APPEARS THE SAME EVERYWHERE

2) As the Universe expands, new matter is constantly being created

3) this means that the density of the Universe is always roughly the same

4) In this theory, there is no beginning or end to the Universe

What two theories for the Creation of the Universe prove that it has changed over time?

- The 'Steady State Theory'

- The 'Big Bang Theory'

What is the Big Bang Theory based on?

1) the universe started with an explosion

2) initially all the matter in the universe occupied a very small space

3) this tiny space was very dense

4) then it 'exploded' and kept expanding

5) the finite age for the universe is around 13.8B years

⭐️⭐️Exam question⭐️⭐️

Explain the difference between the geocentric and heliocentric models of the Solar System (1 mark)

(1) the geocentric system states that all space bodies ORBIT THE EARTH whereas the heliocentric mode, states that all space bodies ORBIT THE SUN

⭐️⭐️Exam question⭐️⭐️

Give 2 differences between the 'Steady State' and 'Big Bang' Theories

- Steady State theory states that there is no end to the universe, Big Bang Theory states that the universe has a finite age (13.8B yrs)

- Steady State theory states that the Universe has always existed as it has now, Big Bang theory states that the Universe started as a dense tiny space.

What does red-shift suggest about the universe?

That the universe is expanding

What is the absorption spectrum?

a spectrum of electromagnetic radiation transmitted from the Sun showing dark lines due to absorption of specific wavelengths in the Sun's atmosphere.

What does the absorption spectrum look like?

black lines on a rainbow background, from the longest wavelengths of light (red) to the shortest wavelengths of light (violet)

In red-shift, Why are some wavelengths of light absorbed by the Sun's atmosphere

Due to the elements in the sun's atmosphere

What does the absorption spectrum look like when looking at light received from distant galaxies?

The dark lines are in the same pattern but shifted to the red need of the spectrum 'red-shift'

What does red-shift occur?

Universe is expanding -> Galaxies are moving further and further away -> Light waves get stretched as they make their way to Earth -> increased wavelength -> towards red end which has the longest wavelength

What is a logical explanation for the Big Bang that we is happening today?

If the universe is expanding, it must have been smaller before, and it must have been so tiny that it was just a dense spot, just like in the Big Bang Theory

Explain the Big Bang in less than 30 words

All the matter in the Universe was in one tiny dense, really hot spot. It became so hot that it exploded and started expanding and still is.

When red shift occurs and the light's wavelength increases, what happens to their frequency

It decreases