Physics IGCSE Topic 6 - Space Physics

What does the solar system contain?

The Sun, Eight Planets, Minor planets, Moons, Smaller Solar System Bodies which include asteroids and comets

Eight Planets in Order

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune,

Minor Planets

Include dwarf planets and asteroids

Smaller System Bodies

Comets and Natural Satellites

What is the differences between the four planets closer and the four planets farthest from the sun?

Four Planets Nearest are rocky and small, Four planets farthest are gaseous and large

Accretion Model for Solar System Formation

Approximately 4.6 billion years ago, the solar system was a cloud of interstellar dust and gas known as a solar nebula.

o The gas in the cloud was mostly hydrogen, with some helium

o Interstellar dust is no ordinary dust- it has tiny grains of matter formed from metallic elements such

as magnesium, silicon, iron, an also molecules such as ammonia, carbon monoxide, methane and

nitrogen

o A shockwave from an exploding star (a supernova) began the process of this cloud coming together o Gravity collapsed the material in on itself as it began to spin.

o The centre of the accretion disc was bulged because it contained most of the mass of the cloud.

o High pressure and temperature at the centre of this bulged forced hydrogen nuclei to join together

to make helium nuclei.

o In this process called fusion, enormous energy is released

o The centre of the cloud was now a star our Sun in the center of the nebula.

o With the rise of the sun, the remaining material began to clump together.

o Small particles drew together, bound by the force of gravity, into larger particles – the planets,

minor planets and dwarf planets were formed from these larger pieces.

o The asteroids and comets are the leftover pices that could not form larger objects.

o The solar wind swept away lighter elements, such as hydrogen and helium, from the closer regions,

leaving only heavy, rocky materials to create terrestrial worlds.

o But farther away, the solar winds had less impact on lighter elements, allowing them to coalesce

into gas giants. In this way, asteroids, comets, planets and moons were created.

Strength of a gravitational field (Space)

• At the surface of a planet depends on the mass of the planet

• Around a planet decreases as the distance from the planet increases

What contains most of the mass in a solar system?

The sun. This explains why the planets orbit the sun

What force keeps objects in orbit around the sun?

The gravitational attraction of the sun

What are the characteristics of the sun?

• Star of medium size

• Mostly hydrogen and helium

  • Radiates most of its energy in the infrared, visible and ultraviolet regions of the em spectrum

What are galaxies made up of

Billions of star

Where is the sun?

A star in a galaxy known as the Milky Way galaxy

How far are other stars in the Milky Way?

Much further away from the Earth than the Sun is from the Earth

How are astronomical distances measured?

Light years: Distance travelled in the vacuum of space by light in one year.

The Milky Way

One of many billions of galaxies making up the Universe.

Diameter of the Milky Way

100 000 light years

Redshift

An increase in the observed wavelength of the electromagnetic radiation emitted from receding stars and galaxies.

How does light from distant galaxies appear?

It appears redshifted in comparison with the light emitted on Earth.

What is an evidence for the Big Bang Theory

The redshift in the light from distant galaxies

The Earth as a planet

A planet that rotates on its axis, which is tilted, once in approximately 24 hours,

How much time does it take the earth to orbit the sun

365 days

How does earth’s orbit around the sun affect seasons?

The Earth orbits the Sun once in approximately 365 days.

• The periodic change of climate over the months – is not a result of Earth approaching or moving away from the Sun.

• Seasonal climatic variations are due to the slight tilt of the Earth, which spins like a top tilted at an angle of 23.5 degrees in relation to its orbital path.

• This tilt explains why one hemisphere receives more sun than the other at a given time of year.

How long does it take the moon to orbit the Earth?

Approximately one Month

How does the moon’s orbit around the Earth influence the periodic nature of the Moon’s cycle of phases?

• It takes approximately one month for the Moon to orbit the Earth

• The Moon produces no visible light of its own

• It shines only by reflected sunlight

• The Moon's rotation period is equal to its orbital period:

• The Moon completes 1 rotation about its axis in the same time as it completes 1 orbit around the Earth.

• As a consequence, the Moon always keeps the same face towards the Earth.

• Near Side: hemisphere facing towards the Earth

• Far Side: hemisphere facing away from the Earth

Define average orbital speed:

V = 2πr/T where r is the average radius of orbit and T is the orbital period

What type of orbit do planets, minor planets and comets have?

Elliptical orbits. The sun is not at the center of the orbit except when the orbit is approximately circular

How does gravitational field strength change as objects get farther away from the sun?

It decreases, as well as orbital speed

When does an object in an elliptical orbit travel faster?

When closer to the sun.

Why does an object in an elliptical orbit travel faster? (In terms of conservation of energy)

The total energy of an orbiting planet is the sum of its kinetic and potential energies.

• KE=12(𝑚𝑣2)

• PE = -G(𝑀𝑚) – not

𝑟

required on this course.

• We can see from the two equations that as the distance between the planet and the Sun ( r ) decreases, the

potential energy decreases (gets farther from zero)

 and as the distance between the planet and the Sun increases, the potential energy approaches zero.

 Similarly, the kinetic energy must also change proportionately.

How are stars powered?

By Nuclear reactions that release energy

What are nuclear reactions in a stable star comprised of?

Fusion of hydrogen into helium

What is one light year in metres?

9.5×10¹⁵m

Life Cycle of a star

1. A star is formed from interstellar clouds of

gas and dust that contain hydrogen

2. a protostar is an interstellar cloud collapsing

and increasing in temperature as a result of

its internal gravitational attraction

3. A protostar becomes a stable star when the

inward force of gravitational attraction is

balanced by an outward force due to the high

temperature in the centre of the star

4. All stars eventually run out of hydrogen as

fuel for the nuclear reaction

5. Most stars expand to form red giants and

more massive stars expand to form red

supergiants when most of the hydrogen in

the centre of the star has been converted to

helium

6. A red giant from a less massive star forms a

planetary nebula with a white dwarf star at

its centre

7. A red supergiant explodes as a supernova,

forming a nebula containing hydrogen and

new heavier elements, leaving behind a

neutron star or a black hole at its centre

8. The nebula from a supernova may form new

stars with orbiting planets

What is CMBR

Cosmic microwave radiation. Radiation of a specific frequency observed at all points in space around us

How was CMBR produced

Shortly after the Universe was formed. The radiation has been expanded into the microwave region of the electromagnetic spectrum as the Universe expanded.

How can the speed v of a galaxy moving away from Earth be measured?

The change in wavelength of the galaxy’s starlight due to redshift

How can the distance d of a far galaxy be determined?

Using the brightness of a supernova in that galaxy.

Hubble Constant H₀

The ratio of the speed at which the galaxy is moving away from the Earth to its distance from Earth.

Hubble Constant Equation

H_{0 = v/d}

Current estimate for H₀

2.2 × 10^-18 per second

Age of the universe

d/s = 1/H₀

d/s = 1/H₀

Represents an estimate for the age of the universe and is an evidence for the idea that all matter in the universe was present at a single point