Scroll
Everything that exists is made of atoms which are super small particles that arrange together to create everything.
Everything everywhere is made of tiny particles that are always moving. When things get hotter, the particles speed up. There are gaps between particles, and they're attracted to each other kind of like magnets.
In solids, the particles are packed really tightly together and they can only vibrate on the spot. They can't actually move around freely, which is why solids keep their shape and don't change size.
In liquids, the particles are still close together, but they can actually slide past each other. That's why liquids keep the same volume but take the shape of whatever container you pour them into.
Gas particles are spread really far apart and zoom around super fast in every direction. They don't have a set shape or volume at all. They just spread out to fill whatever space they're in, and you can squish them down easily because of all the gaps between particles.
When you heat something up, the particles get more kinetic energy and start moving faster. If you add enough heat, the state of matter actually changes:
And if you cool it down, it works the other way: gas condenses back into liquid, and liquid freezes into a solid. One cool thing I learned is that during a change of state, the temperature actually stays the same because all the energy goes into breaking or making bonds between particles instead of making them move faster.
Changes of state, adding heat energy causes melting and evaporation, removing heat energy causes condensation and freezing.
Stars are born when huge clouds of interstellar gas compress under gravity. When temperatures reach 30 million °C, nuclear fusion starts and a star is born.
It starts with massive clouds of hydrogen and helium gas getting pulled together by gravity.
Gravity pulls gas and dust togetherAs all that matter gets squished together, the core heats up and the protostar starts to glow.
Forms into protostarOnce it hits 30 million °C, fusion starts up. The star settles down because the outward pressure balances out with gravity.
Hydrogen fusion at 30,000,000°CEventually the hydrogen runs out, so the star switches to helium. It gets even hotter and grows up to a huge size.
Helium fusion startsslowly burns hydrogen for billions of years
Grows into a Red Giant
The core runs out of fuel and the star implodes
It slowly cools into a White Dwarf, and eventually becomes a cold Black Dwarf
Burns through hydrogen way faster, in just millions of years
Expands into a Red Giant
Collapses and explodes in a massive Supernova!
Becomes a Neutron Star, Pulsar, or Black Hole
The Earth is tilted on its axis at about 23.5°. This tilt means the Sun's heat doesn't fall equally on both hemispheres all year giving us seasons.
Earth rotates once every 23 hours, 56 minutes and 4 seconds. It also orbits the Sun, taking 365.25 days to complete one orbit.
An Astronomical Unit is the average distance from the Earth to the Sun, approximately 150 million km. Scientists use this as a standard measurement for distances within our Solar System.
A sidereal year is the time it takes Earth to complete one full orbit around the Sun compared to the distant stars. It lasts 365 days, 6 hours, 9 minutes and 10 seconds, which is slightly longer than a calendar year.
Earth's axis slowly wobbles in a circle, completing one full wobble every 26,000 years. This is called precession. Over time, it gradually shifts when the seasons occur.
Earth's tilt of 23.5°, causes the seasons by changing the amount of sunlight hitting each hemisphere.
When a hemisphere is tilted toward the Sun, the Sun's rays hit more directly, aiming energy on a smaller area, this is summer.
When tilted away, light hit at an angle and spread over a larger area, this is winter.
Hemisphere tilted toward the Sun. Direct light, longer days.
Moving away from the Sun. Days shorten, temperatures colder.
Hemisphere tilted away. angled rays, less light, shorter days.
Moving back toward the Sun. Days lengthen, temperatures warmed.
Around June 21 in the Southern Hemisphere. The Sun is at its lowest point in the sky, giving us the shortest day and longest night. The Sun's light hit at a very low angle, spreading energy over a larger area.
Around December 21 in the Southern Hemisphere. The Sun is at its highest point in the sky, giving us the longest day and shortest night. The Sun's light hits more directly, concentrating energy.
The angle of incidence is the angle at which the Sun's light strikes the Earth's surface. When the angle is high, the energy is concentrated on a small area and it feels hotter. When the angle is low, the same energy is spread across a much larger area, so it feels cooler. This is the main reason seasons have different temperatures.
Many Aboriginal and Torres Strait Islander peoples recognise more than four seasons, based on careful observation of natural changes like animal behaviour, plant cycles, wind patterns, and rainfall, rather than just temperature.
For example, the D'harawal people of the Sydney region recognise six seasons:
Season of the Mists (Febuary).
Season of the Lyre Bird (March and April).
Season of the Kangaroo (May and July).
Season of the Willy Wagtail (July and August).
Season of the Flying Foxes (September and October).
Season of the Warm Winds (November and December).
Unlike the four-seasons based on the calendar, First Nations seasons are based on what is happening in the natural environment. The number and time of seasons changes between different nations across Australia, based on the local climate of each Country.
23 hours, 56 minutes and 4 seconds the time Earth takes to rotate once on its axis.
29.5 days the time the Moon takes to orbit Earth once.
365.25 days the time Earth takes to orbit the Sun once.
About 30 Earth days the same length as a Moon year, which is why we always see the same side.
The Moon's appearance changes constantly as it orbits Earth. The Sun can only light up half the Moon at any time we see different amounts each night.
The Moon orbits Earth in an anticlockwise direction, taking approximately 27.3 days (a sidereal month) to complete one orbit. It also rotates on its own axis in the same time.
The Moon is tidally locked to Earth, meaning it rotates on its axis in exactly the same time it takes to orbit Earth. This is why we always see the same face of the Moon.
The point in the Moon's orbit where it is farthest from Earth, at about 405,500 km away. At apogee, the Moon appears slightly smaller in the sky.
The point in the Moon's orbit where it is closest to Earth, at about 363,300 km away. A full moon at perigee is called a Supermoon and appears about 14% larger and 30% brighter.
The complete lunar cycle takes 29.5 days. Each phase lasts roughly 3.7 days as the Moon moves through its cycle.
Waxing
← Waning
The 8 phases of the Moon across a 29.5-day synodic month. Each phase lasts approximately 3.7 days.
Alignment: Sun and Moon → Earth
When the Moon passes between the Earth and Sun, blocking some or all sunlight. A total eclipse occurs when Sun, Moon, and Earth are in a straight line, visible only from a small section of Earth.
Alignment between Sun → Earth → Moon
When Earth passes between the Moon and Sun, blocking sunlight from reaching the Moon. Earth's shadow passes across the face of the Moon.
Tides are the regular rise and fall of sea levels caused by the gravitational pull of the Moon and, to a lesser extent, the Sun on Earth's oceans.
The Moon's gravity pulls on Earth's oceans, creating a bulge of water on the side of Earth closest to the Moon (direct tide). At the same time, on the opposite side of Earth, inertia creates another bulge (indirect tide). This gives most coastlines two high tides and two low tides each day, roughly 6 hours apart.
The Sun also pulls on Earth's water, but because it is much farther away, its tidal force is about half that of the Moon.
Sun — Moon — Earth aligned (syzygy)
Spring tides (also called King tides) occur when the Sun, Moon and Earth are aligned in a straight line (during a new moon or full moon). The gravitational forces of the Sun and Moon combine together, creating:
These happen roughly twice a month.
Sun — Earth — Moon at 90° (quadrature)
Neap tides occur when the Sun and Moon are at right angles (90°) to each other relative to Earth (during first quarter and last quarter moon). Their gravitational forces partially cancel out, creating:
These also happen roughly twice a month.
Sun and Moon are on the same side of Earth. Their gravitational pulls add together, producing the highest tides.
Sun and Moon are on opposite sides of Earth. Their pulls still align along the same axis, producing high tides.
The Moon is at 90° to the Sun relative to Earth. The pulls work against each other, producing smaller tides.
The Moon is again at 90° to the Sun, just on the other side. Another period of smaller, weaker tides.
Throughout history, advances in technology have transformed our understanding of the Universe. Each new instrument lets us see further back in time and deeper into space.
Since Galileo first turned a telescope to the sky in 1609, optical telescopes have helped us discover planets, moons, and distant galaxies. Modern ground-based telescopes like the Very Large Telescope in Chile can see objects billions of light years away.
The Hubble Space Telescope (1990) orbits above Earth's atmosphere, giving us crystal-clear images of distant galaxies. The James Webb Space Telescope (2021) uses infrared to see even further, detecting light from the first galaxies formed after the Big Bang.
Radio telescopes detect radio waves from space, revealing objects invisible to the human eye like pulsars and quasars. In 1965, Penzias and Wilson accidentally discovered the Cosmic Microwave Background radiation, the leftover heat from the Big Bang, providing key evidence for how the Universe began.
Unmanned spacecraft like the Voyager probes (1977) have explored the outer planets and are now in interstellar space. The COBE satellite (1992) mapped heat variations in the cosmic background, and Mars rovers like Curiosity analyse the planet's surface and past water activity.
By splitting light into its spectrum, scientists can determine what elements stars and galaxies are made of, how fast they're moving, and how far away they are. This technology confirmed the red shift and the expanding Universe.
In 2015, LIGO detected ripples in spacetime caused by two black holes colliding 1.3 billion years ago. This opened an entirely new way to observe the Universe and understand violent cosmic events from the distant past.
Because light takes time to travel, when we look at distant objects we are literally seeing the past. The James Webb Space Telescope can see galaxies as they were over 13 billion years ago, just a few hundred million years after the Big Bang. Every improvement in technology lets us look further back, building a more complete picture of how the Universe formed and evolved.
Think you've learnt it all? Take this quiz to find out!
The Universe began about 15 billion years ago in a massive explosion. Everything that exists, all stars, planets, galaxies, and the space between them was born from this single moment.
Most astronomers beleive all matter was created in an instant and started expanding outwards in an enormous explosion called the Big Bang.
The Universe has no centre and no edges it is infinite. Everything is expanding outwards in every direction forever.
Edwin Hubble found out that light from distant galaxies shifts toward the red end of the colour spectrum, proving galaxies are moving away from us.
The Cosmic Background Explorer found small heat wave ripples which might be left over from the Big Bang explosion.
A huge amount of energy was created in an instant started the Big Bang.
The Universe was very, very small, made up of only energy. It started to expand outwards in every direction.
As the Universe expanded, it cooled from its original 10 billion degrees.
At about 3000°C, hydrogen and helium atoms started to form.
Gas atoms in denser parts of the fog were pulled together into individual small clouds with big spaces between them.
Gravity pulled atoms closer, and lumps of matter started to form inside the gas clouds.
Temperature within the lumps rose to 30 million °C, hydrogen fusion started. The first stars were born.
Millions of stars grouped together through gravitational forces to form galaxies.
Galaxies stay as essential groups while the growing of the Universe continues.
Our Sun formed about 4.6 billion years ago. A dust cloud of elements came together to form the planets.
The Universe may go on growing forever, with gravitational forces between galaxies being too weak to slow or stop the expansion.
Or expansion may slow down as gravitational forces attract galaxies together, leading to a Big Crunch then a new Big Bang all over again!
The oldest galaxies in the Universe. They don't have nebulae, meaning they have no way to produce new stars. The largest galaxies are giant ellipticals.
Like the Andromeda galaxy(our closest galaxy) spirals of stars thrown out from a small central nucleus. The spirals can be loose or tight.
Like our Milky Way! They have an long central bar rather than a sphere nucleus, with spiral arms swirling from the bar's ends.
No particular shape. The Magellanic Clouds are irregular, possibly pulled out of shape by gravitational forces from nearby galaxies.
About 20% of stars have a partner! Two stars orbit each other, some in just hours, others taking years. Binary systems can produce the brightest supernovas.