Year 10 Earth and Space Science

What are stars mainly made of?

Hydrogen and helium.

What is nuclear fusion?

Small atomic nuclei combine, releasing energy.

What happens during fusion in the Sun?

Hydrogen nuclei combine to form helium, releasing heat and light.

What is a star's mass?

The amount of matter in the star.

How does mass affect a star's life?

Mass affects its temperature, brightness, lifespan and death.

How do high-mass stars compare with low-mass stars?

High-mass stars are hotter, brighter, bluer and shorter-lived.

What is apparent magnitude?

How bright a star appears from Earth.

What is absolute magnitude?

A measure of how bright a star would appear at a standard distance of 10 parsecs.

What is a light-year?

The distance light travels in one year.

How many light-years are in one parsec?

Approximately 3.26 light-years.

How do you convert parsecs to light-years?

Multiply the number of parsecs by 3.26.

How do you convert light-years to parsecs?

Divide the number of light-years by 3.26.

What is parallax?

The apparent shift of an object viewed from different positions.

How is parallax used to measure star distances?

Measure a nearby star's apparent shift from two positions in Earth's orbit.

When are stars usually observed for parallax?

Six months apart, from opposite sides of Earth's orbit.

Which stars show greater parallax?

Nearby stars show greater apparent shifts.

What determines a star's colour?

Its surface temperature.

Which stars are hottest: red or blue?

Blue stars are hotter than red stars.

What is luminosity?

The total energy a star releases per second.

What does an H-R diagram compare?

Stars' temperature/colour and luminosity.

Where are hot, bright stars on an H-R diagram?

Near the top left.

Where are cool, dim stars on an H-R diagram?

Near the bottom right.

Where are giants on an H-R diagram?

Generally towards the upper right; they are cool but bright.

Where are white dwarfs on an H-R diagram?

Near the lower left; they are hot but dim.

Where is the Sun on an H-R diagram?

On the main sequence, with medium temperature and brightness.

How do galaxies form?

Gravity pulls gas and matter together into large structures.

What is a nebula?

A large cloud of gas and dust where stars form.

What is a protostar?

A forming star created as gravity pulls gas together.

What is the main sequence stage?

The stable stage when a star fuses hydrogen into helium.

What two forces balance in a main sequence star?

Gravity pulls inward; energy from fusion pushes outward.

What is a red giant?

A star that expands in a later stage of its life.

What is a white dwarf?

A small, dense remnant of a low-mass star.

What is a supernova?

A huge explosion that can mark the end of a massive star.

What is a neutron star?

An extremely dense remnant left after a massive star's supernova.

How does a neutron star form?

Gravity compresses matter so electrons combine with protons to form neutrons.

What is a pulsar?

A rapidly rotating neutron star whose radiation beams sweep through space.

How does a black hole form from a massive star?

After a supernova, the remaining material collapses under extreme gravity.

What is an event horizon?

The boundary beyond which light cannot escape a black hole.

What is a singularity?

The extremely small central region into which matter collapses in a black hole.

What is an accretion disk?

A disk of gas and dust being pulled towards a black hole.

What happens when a star runs out of hydrogen?

It leaves the main sequence; its later stages depend mainly on its mass.

What is the basic life cycle of a low-mass star?

Nebula → protostar → main sequence → red giant → white dwarf.

What is the basic life cycle of a massive star?

Nebula → protostar → main sequence → red supergiant → supernova → neutron star or black hole.

What determines whether a massive star leaves a neutron star or black hole?

The mass remaining after the supernova.

What is the Big Bang theory?

The observable universe began in a very dense state and has expanded ever since.

Approximately how old is the universe according to your notes?

About 13.7 billion years.

Was the Big Bang an explosion into existing space?

No. It describes the expansion of space itself.

What is redshift?

Light's wavelength becomes longer as it is stretched.

What does redshift suggest about distant galaxies?

Many are moving away from us, providing evidence that the universe is expanding.

What is blueshift?

Light's wavelength becomes shorter when a source moves towards the observer.

What happened as the early universe expanded?

The universe grew larger and cooled, allowing structures to form over time.

What is the approximate width of the observable universe in your notes?

Approximately 92 billion light-years.