4.8 Space physics

How many stars are in our solar system?

There is only one star in our solar system: the sun, which sits at the centre

Describe what makes up our solar system

Our solar system is heliocentric; the sun is in the centre.

• One star, the Sun

• Eight planets that orbit the sun

• Dwarf planets which orbit the sun

• Moons that orbit planets

Name all the planets in our solar system in order of closest to the sun

Eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

My very educated mother just served us nachos (planets)

What galaxy is our solar system a part of?

The milky way

What are the difference between planets and moons?

Planets orbit stars, whereas moons are natural satellites that orbit planets.

What are nebulas?

Clouds of gas and dust

Describe how stars (eg. the sun) are formed

• Nebulas (clouds of gas and dust) are formed in the galaxy.

• The gravitational attraction between the gas and dust particles of the nebula pull them closer together, forming a protostar.

• As the particles get closer, the protostar becomes denser and the gas and dust particles collide more frequently with each other,

• causing the temperature and pressure of the protostar to increase.

• Eventually the temperature and pressure of the protostar becomes so great that lighter nuclei (mainly hydrogen nuclei) undergo nuclear fusion

• to form helium nuclei.

• This releases large amounts of energy, which keep the core of the star hot.

• The force exerted by pressure due to the energy released by nuclear fusion balances the inward force of gravity.

• which leads to an equilibrium between the gravitational collapse of the star and the expansion of the star.

• This means that a star has formed; the star enters a long stable period

In the stable period it is called a main sequence star, and it typically lasts several billion years

What does the life cycle of a star depend on?

Its size

Draw the life cycle of a star

State the life cycle of a star about the same size as our Sun

• Cloud of gas and dust (nebula)

• Protostar

• Main sequence star

• Red giant

• White dwarf

• Black dwarf

State the life cycle of a star much bigger than our Sun

• Cloud of gas and dust (nebula)

• Protostar

• Main sequence star

• Red super giant

• Supernova

• Neutron star or black hole

How are naturally occurring elements produced?

By fusion processes in stars

Describe the life cycle of a star about the same size of our Sun after it has become a main sequence star

• The main sequence star will carry on undergoing fusion reactions until the hydrogen runs out in the core

• When the hydrogen runs out, fusion can no longer occur so the star is no longer at equilbrium; it will collapse

• As the star collapses, the temperature and pressure of its core increases, meaning heavier elements can fuse together (helium nuclei), forming even heavier elements (eg. carbon, oxygen)

• As the star fuses the heavier elements, it releases more energy which causes the star to swell

• As the surface of the star gets further away from its core, its surface cools, forming a red giant

• Once all fusion stops,

• the red giant becomes unstable and collapses

• and ejects its outer layer of dust and gas (forming a planetary nebula)

• This leaves behind a hot, dense solid core - a white dwarf

• Over millions of years, the white dwarf will cool down and emit less and less energy

• When it no longer emits a significant amount of energy, it becomes a black dwarf

Describe the life cycle of a star much larger than our Sun, after it has become a main sequence star

• The main sequence star will carry on undergoing fusion reactions until the hydrogen runs out in the core

• When the hydrogen runs out, fusion can no longer occur so the star is no longer at equilbrium; it will collapse

• As the star collapses, the temperature and pressure of its core increases, even meaning heavier elements can fuse together (helium nuclei), forming even heavier elements (eg. carbon, oxygen)

• The main sequence star will then form a red super giant as the surface of the star cools

• The red super giant continues to glow brightly and undergo more fusion reactions, releasing more energy

• expanding and contracting several times

• and forming elements as heavy as iron in various fusion reactions

• Eventually, once all fusion has occurred, the star is too large to be stable so collapses and rebounds on its centre, exploding to produce a supernova

• The supernova forms elements heavier than iron and ejects them into the universe, allowing them to form new planets and stars

• The exploding supernova ejects the outer layers of dust and gas into space

• Once the supernova has exploded, the leftover core will be called a neutron star, or if the star was very large it will become a black hole

Explain how new elements are formed

• Fusion reactions that occur in stars form new elements (eg. at very high temperatures hydrogen nuclei fuse to form helium)

• When large stars form red super giants, even heavier elements can form due to higher core temperatures (eg. iron) in fusion reactions

• When stars explode into supernovas, even heavier elements can form

They are distributed when the star explodes into the supernova, as it ejects them into the universe

What is acceleration?

The rate at which the velocity of an object changes

What causes planets and satellites to maintain orbits?

Gravity provides the force that allows planets and satellites (both natural and artificial) to maintain their circular (or almost circular) orbits

Describe the similarities and differences between the planets, their moons and artificial satellites

Planets:

• Natural

• Orbit a star

• Elliptical orbit

Moons:

• Natural

• Orbit a planet

• Circular/ almost circular orbit

Artificial satellites:

• Made by humans

• Orbit a planet (usually Earth)

• Circular/ almost circular orbit

Explain and describe the motion of a body in orbit

• The force of gravity holds bodies in their orbit

• Constant speed

• But changing velocity

• As velocity is a vector quantity that measures the speed and direction of an object

• And the direction of an object in circular orbit is always changing

Explain the relationship between the radius of an object’s orbit and its speed

• The closer towards a star/ planet, the stronger the gravitational force is

• The stronger the force, the faster the orbiting object needs to travel to remain in orbit (to not crash into the object that it’s orbiting)

For an object in stable orbit, if the speed of the object changes, the radius of its orbit must do so to.

Faster orbit = smaller radius

Slower orbit = larger radius

What is the red shift?

• There is an observed increase in the wavelength of light from most distant galaxies

• The further away the galaxies, the faster they’re moving away and the bigger the observed increase in wavelength

• This is the red shift - as the wavelengths are longer then they should be, this means that they have shifted to the red end of the spectrum

• This shows that the universe is expanding

What does the red shift provide evidence for?

• That space itself (the universe) is expanding

• This supports the big bang theory

Describe the big bang theory

• The big bang theory suggests that the universe began from a very small region that was extremely hot and dense

• At some point there was a ‘big bang’ when the hot, dense area of matter exploded

• The matter all began to move away from each other, meaning that the universe at that point was expanding

Not much is understood about the universe; give examples of concepts that are still not understood

• Dark mass

• Dark energy

What galaxies have the greatest red shift and why?

Very distant galaxies have a very large red shift as they are moving away very fast

What is the shape of planetary orbit?

Elliptical