Astronomy revision

What is the definition of the universe?

The universe is all of the matter and energy that exists in space and time.

What is the observable universe?

The observable universe is the portion of the universe that we can see or detect from Earth, limited by the speed of light and the age of the universe.

List common astronomical objects.

Stars, planets, moons, asteroids, comets, galaxies, nebulae, and black holes.

What is our cosmic address?

Earth → Solar System → Oort Cloud, Local Interstellar Cloud, Local Cavity, Orion Arm, Milky Way, Local Group, Virgo Supercluster, Laniakea Supercluster, the Universe.

Describe common astronomical objects.

• Stars: Massive, luminous spheres of plasma (e.g., the Sun).

• Planets: Large bodies orbiting stars (e.g., Earth).

• Galaxies: Massive systems of stars, gas, and dust (e.g., Milky Way).

• Nebulae: Clouds of gas and dust where stars form.

• Black Holes: Regions with gravity so strong that nothing can escape.

What is a scientific theory?

A well-substantiated explanation acquired through the scientific method and repeatedly tested and confirmed through observation and experimentation.

What is the Big Bang Theory?

The theory that the universe began from an extremely hot and dense state around 13.8 billion years ago and has been expanding ever since.

List the events that took place following the Big Bang.

Cosmic inflation, First particles, First nuclei, First light, first stars, first galaxies, dark energy.

Describe the events that took place following the Big Bang.

After the Big Bang, the universe rapidly expanded and cooled, allowing for the formation of subatomic particles, atoms, and galaxies. After billions of years, galaxies were formed, stars underwent lifecycles, and new elements were synthesised in stellar cores. The universe continues to expand and evolve, with galaxies moving away from each other due to the expansion of the universe.

How do scientific theories change over time?

Scientific theories are refined or rejected as new evidence emerges, leading to better explanations of natural phenomena.

Compare and contrast the Big Bang and Steady State theories. (Steady state theory)

Steady state theory:

• There is no beginning to the universe

• New matter is constantly being created to form new stars and galaxies

• The density of the universe does not change over time

Compare and contrast the Big Bang and Steady State theories. (Big bang theory)

Big bang theory:

• The universe began as an extremely hot state

• The amount of matter stays the same throughout time

• The density of the universe decreases over time

List the scientific evidence that supports the Big Bang Theory

1. Redshift of galaxies (Hubble's Law).

2. Cosmic microwave background radiation.

3. Abundance of light elements (hydrogen and helium)

What is redshift, and what is cosmic microwave background radiation?

Redshift: The stretching of light waves from galaxies, shifting towards the red end of the spectrum, indicating an expanding universe.

Cosmic microwave background radiation: leftover heat from the Big Bang, emitted about 380,000 years was thinly spread across all directions in space. Therefore supporting that the the universe was once hot and is now cooling

How can you identify a galaxy's relative motion from its spectrum?

By observing redshift (moving away) or blueshift (moving closer) in the galaxy's spectral lines (black lines).

How does evidence support or reject theories of the universe's origin?

Evidence like redshift, CMB, and element abundance supports the Big Bang, while inconsistent observations and a lack of evidence to support your reasoning challenge the evidences

What is the definition of a star?

Stars are massive balls of hot gas consisting of mostly hydrogen, some helium, and small amounts of other elements.

Recall the life cycles of stars with low and high initial masses.

Low mass star: Nebula → Protostar → Main sequence star → Red giant → Planetary nebula → White dwarf → Black dwarf

High mass star: Nebula → Protostar → Main sequence star → Red supergiant → Supernova → Neutron star → Black hole

What is stellar nucleosynthesis?

The process within stars where electrons would combine to form atoms, leading to the formation of new elements.

Describe the stages of a star's life cycle (low mass)

Nebula - Large clouds of gas and dust

Protostar - A contracting and spiralling cloud of gas and dust. The gravitational pull gets increased and the core becomes denser and begins to heat up.

Main sequence star - Stars are in a stable phase where nuclear fusion(when the core becomes hot enough so that hydrogen fuses to form helium) pushing outwards is balanced by the gravitational pull inwards. Less matter from the nebula is accumulated to form a low mass star

Red Giant - The star collapses in on itself due to hydrogen deficiency and then the outward pressure will increase. After that, it then begins to expand and forms a larger star

Planetary Nebula - As red giants continue to expand, the force of gravity decreases making the outer layers of red giant drift into space creating a cloud of gas and dust

White dwarf - The remaining core of the star

Black dwarf - When all the fuel has been used up by the core, it then becomes the black dwarf.

Describe the stages of a star's life cycle (high mass)

Nebula - Large clouds of gas and dust

Protostar - A contracting and spiralling cloud of gas and dust. The gravitational pull gets increased and the core becomes denser and begins to heat up.

Main sequence star - Stars are in a stable phase where nuclear fusion(when the core becomes hot enough so that hydrogen fuses to form helium) pushing outwards is balanced by the gravitational pull inwards. More matter from the nebula is accumulated to form a high mass star.

Red supergiant - High mass stars will form red supergiants and have stronger gravitational force. They are larger than red giants and undergo larger nuclear fusion to form heavier elements like iron.

Supernova - When red supergiants run out of fuel, the core rebounds causing a shockwave that blows out the outer layers. The shockwave compresses matter creating new elements like zinc, gold and uranium.

Neutron stars - All that is left after the supernova is a very dense core of the star. The gravitational pressure crushes electrons and protons together, leaving a star composed of mostly neutrons.

Black hole - If the neutron star is big enough, then a black hole will form. The black hole is so dense that the force of gravity is too powerful to allow light to escape.

Explain the life cycle of our Sun.

The Sun formed 4.6 billion years ago from a collapsing cloud of gas and dust, igniting nuclear fusion in its core. It is now in the main sequence phase, steadily burning hydrogen into helium, and will remain stable for about 5 billion more years. Eventually, it will expand into a red giant, shed its outer layers, and end as a white dwarf.

How did Australian Indigenous peoples use the stars?

They used stars for navigation, timekeeping, storytelling, and cultural practices.

Why are Australian Indigenous peoples considered the first astronomers?

They observed and documented celestial phenomena for tens of thousands of years, using this knowledge in their daily lives.

What is an exoplanet?

A planet that orbits a star outside our solar system.

What is the 'habitable zone'?

The region around a star where planets may have water, making life possible.

What is a galaxy?

A massive system of stars, gas, dust, and dark matter bound together by gravity.

List and describe the three types of galaxies.

1. Spiral: Disk-shaped with spiral arms (e.g., Milky Way).

2. unbarred (no line across centre)

3. Elliptical: Round or oval-shaped, with little gas or dust - forms from 2 older galaxies - all old stars

4. Irregular: No defined shape, often chaotic. old and new stars present

How do galaxies evolve over time?

Galaxies evolve through collisions, star formation, and interactions with other galaxies, often growing larger and more complex.

What does both the Steady State and Big Bang Theory believe?

They both believe that the universe is always expanding.