The Solar System & Lifecycles of Stars Flashcards
All 42 cards in this deck
What is the equation for weight?
weight (N) = mass (kg) × gravitational field strength (N/kg)
What is the value of the gravitational field strength at the surface of the Earth?
About N/kg
Which two properties of a body in space determine the value of at its surface?
Its mass and its radius.
Greater mass gives larger ; larger radius gives smaller .
What are the steps to calculate the weight of an object on another body in space?
e.g. a 60 kg astronaut on the Moon, where N/kg
- Use
- Use the for that body:
- Weight N
True or false? An astronaut's mass is smaller on the Moon than on Earth.
False. Mass is the same everywhere; it is the weight that is smaller because is smaller on the Moon.
True or false? Two planets with the same mass have the same at their surfaces.
False. The planet with the larger radius has the smaller surface .
What does our Solar System consist of?
The Sun (our star), eight planets and their natural satellites (moons), dwarf planets, asteroids and comets.
Name the eight planets in order of distance from the Sun.
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
What is the geocentric model of the Solar System?
The old model with the Earth at the centre, with the Sun, Moon and planets orbiting the Earth.
What is the heliocentric model of the Solar System?
The accepted model with the Sun at the centre and the planets orbiting the Sun.
Give one observation made with early telescopes that supported the heliocentric model.
Galileo saw moons orbiting Jupiter, showing not everything orbits the Earth.
(Accept: the phases of Venus.)
True or false? Pluto is one of the eight planets of the Solar System.
False. Pluto is now classified as a dwarf planet.
What force keeps a planet or satellite in a circular orbit, and in which direction does it act?
Gravity, acting towards the centre of the orbit (a centripetal force).
For an object in a circular orbit, what stays constant and what changes?
The speed stays constant but the velocity changes, because the direction of motion keeps changing.
True or false? A satellite moving in a circular orbit at constant speed is accelerating.
True. Its direction, and so its velocity, is always changing.
What is a geostationary satellite's orbit like?
A circular orbit above the equator with a period of 24 hours, so it stays above the same point on the Earth's surface.
What is a near-Earth (low) orbit satellite used for?
Monitoring the weather and imaging the Earth's surface; it orbits in a few hours and passes over different parts of the Earth.
How does the orbital period of a planet change with its distance from the Sun?
The greater the orbital radius, the longer the orbital period (and the slower the orbital speed).
e.g. Jupiter takes far longer than Earth to orbit once.
What shape are the orbits of the planets around the Sun?
Slightly elliptical (almost circular), with the Sun at one focus.
What shape is the orbit of a comet?
A very elongated (highly elliptical) orbit around the Sun.
Where in its orbit does a comet move fastest?
When it is closest to the Sun, where the gravitational force on it is greatest.
For a stable orbit, what must happen to the orbital radius if the orbital speed increases?
e.g. a satellite is speeded up
The radius must decrease.
The satellite moves into a lower, faster orbit.
True or false? A satellite in a low orbit travels more slowly than one in a high orbit.
False. The smaller the orbital radius, the faster the satellite must travel for a stable orbit.
What shape are the orbits of moons (natural satellites) around their planets?
Almost circular (slightly elliptical) orbits around the planet.
What is a nebula?
A cloud of dust and gas (mostly hydrogen) in space, from which stars form.
What are the steps by which a nebula produces the conditions needed for nuclear fusion?
e.g. the cloud of gas and dust that formed the Sun
- The nebula collapses under gravity
- Gravitational potential energy is transferred to kinetic energy of the particles, so temperature and pressure rise
- Very high temperature and pressure start hydrogen fusion in the protostar
What is a protostar?
A collapsing cloud of gas and dust that is heating up but has not yet begun nuclear fusion.
Which two effects are balanced in a stable (main sequence) star?
Inward gravity and outward thermal expansion (radiation pressure) from fusion in the core.
True or false? A main sequence star stays the same size because gravity is the only force acting on it.
False. It stays the same size because inward gravity is balanced by the outward thermal expansion caused by fusion.
What happens to the balance in a star when the hydrogen in its core begins to run out?
Fusion in the core slows, so outward thermal expansion no longer balances gravity; the core contracts and the outer layers expand.
List the stages in the life cycle of a star of similar mass to the Sun.
Nebula → protostar → main sequence star → red giant → white dwarf
What happens during the main sequence stage of a star's life?
Hydrogen fuses to helium in the core and the star is stable, with gravity balanced by outward thermal expansion.
What is a red giant?
A star whose core hydrogen has run out, so its outer layers have expanded and cooled, making it larger and redder.
What is a white dwarf?
The hot, very dense core left behind after a red giant sheds its outer layers; no fusion occurs and it slowly cools and fades.
True or false? The Sun will end its life in a supernova.
False. The Sun is not massive enough; it will become a red giant and then a white dwarf.
True or false? A star spends most of its lifetime as a main sequence star.
True. This is its long stable stage, while it fuses hydrogen in its core.
List the stages in the life cycle of a star with a mass much larger than the Sun.
Nebula → protostar → main sequence star → red supergiant → supernova → neutron star or black hole
What is a supernova?
A huge explosion of a red supergiant, which happens when its core collapses.
What is a neutron star?
An extremely dense remnant core left after a supernova.
What decides whether a supernova leaves a neutron star or a black hole?
The mass of the remaining core: the most massive cores become black holes, less massive ones become neutron stars.
What is a black hole?
An object so dense that its gravitational field is strong enough to stop even light escaping.
How does the density of a neutron star compare with that of the Sun?
Far greater — a mass similar to the Sun's is squeezed into a radius of only about km.