Objects & Scale
What is the name of a large collection of stars, gas and dust held together by gravity?
A galaxy.
What is the main source of energy produced by stars?
Nuclear fusion.
What is the name of the explosion that can occur at the end of a massive star's life?
Supernova
What is the force that attracts objects with mass towards one another?
Gravity
What is an astronomical unit (AU)?
The average distance between Earth and the Sun, approximately 150 million kilometres.
What is a protostar?
An early stage of star formation in which gas and dust are collapsing under gravity and heating up, before sustained hydrogen fusion begins.
What is a neutron star?
An extremely dense remnant that can form after the core of a massive star collapses during a supernova.
What is the difference between mass and weight?
Mass is the amount of matter in an object, whereas weight is the gravitational force acting on the object.
Explain one difference between a solar system and a galaxy.
A solar system consists of a star and the objects orbiting it, whereas a galaxy contains billions of stars and their associated systems, along with gas and dust.
Arrange the following stages of star formation in the correct order: main-sequence star, nebula, protostar.
Nebula → Protostar → Main-sequence star.
Identify two possible remnants that can form following a massive star's core-collapse supernova.
Neutron star or black hole.
Explain why the planets orbit the Sun instead of travelling in straight lines through space.
The Sun's gravitational attraction continuously changes the direction of the planets' motion, keeping them in orbit.
Explain why astronomers use light-years rather than kilometres to measure distances between stars.
Distances between stars are extremely large, so using light-years makes these distances easier to express and compare.
Explain how gravity contributes to the formation of a star from a nebula.
Gravity pulls gas and dust together, causing the material to become denser. As it contracts, the temperature increases, eventually allowing nuclear fusion to begin in the core.
Explain why the Sun will not end its life in a typical core-collapse supernova.
The Sun does not have enough mass to undergo the core collapse that produces this type of supernova. Instead, it will expand into a red giant, lose its outer layers and leave behind a white dwarf.
Explain why a person weighs less on the Moon than on Earth, even though their mass remains unchanged.
The Moon has a weaker gravitational field at its surface than Earth. This means the gravitational force acting on the person is smaller, even though the amount of matter in their body remains unchanged.
An astronomer observes a galaxy 2 million light-years away. Explain why the galaxy may look different today compared with what the astronomer observes.
Light from the galaxy takes 2 million years to reach Earth. Therefore, astronomers observe the galaxy as it appeared 2 million years ago, and it may have changed since then.
Two stars are the same distance from Earth. Star A is significantly brighter than Star B.
Explain what this suggests about their luminosities and identify two characteristics that can influence luminosity.
Star A has a greater luminosity. Luminosity is influenced by a star's surface temperature and size (surface area).
Two stars form at the same time. Star A is similar in mass to the Sun, while Star B is 20 times more massive. Predict which star will reach the end of its life first and explain why.
Star B will reach the end of its life first. Its greater mass causes higher core temperatures and much faster nuclear fusion, meaning it consumes fuel more quickly.
A spacecraft travels from Earth to a planet where the gravitational field strength is twice that of Earth. Predict what happens to the spacecraft's mass and weight, and explain why.
Its mass remains unchanged, but its weight doubles. Weight depends on gravitational field strength, whereas mass is independent of location.