Solar System, Stability of Orbital Motions & Satellites Flashcards
All 37 cards in this deck
What objects make up our solar system?
One star (the Sun), the eight planets, dwarf planets and natural satellites (moons); also asteroids and comets.
What is a natural satellite?
A moon — a body that orbits a planet naturally.
Which galaxy is our solar system part of?
The Milky Way galaxy — our solar system is only a small part of it.
True or false? Pluto is one of the eight planets of the solar system.
False. Pluto is a dwarf planet; there are eight planets.
True or false? There is only one star in our solar system.
True. The Sun is the only star; everything else orbits it or orbits a planet.
What is a nebula?
A cloud of dust and gas in space, from which stars form.
What force pulls the dust and gas of a nebula together?
Gravitational attraction (gravity).
What is a protostar?
The hot, dense mass of dust and gas formed as a nebula collapses, before fusion reactions begin.
Why do fusion reactions start in a protostar?
Gravity makes it denser, so the temperature and pressure become high enough for hydrogen nuclei to fuse.
What are the steps by which a star forms?
e.g. how the Sun formed
- Gravity pulls dust and gas in a nebula together.
- The mass gets denser and hotter — a protostar.
- It becomes hot enough for fusion of hydrogen — a main sequence star like the Sun.
Why is a main sequence star stable?
The inward force of gravity is in equilibrium with the outward force due to the energy released by fusion.
Which nuclei fuse in a main sequence star, and what do they form?
Hydrogen nuclei fuse to form helium.
Where do all of the naturally occurring elements come from?
Fusion processes in stars produce all of the naturally occurring elements.
Which elements can only be produced in a supernova?
Elements heavier than iron.
What spreads the elements made in stars throughout the universe?
The explosion of a massive star (a supernova).
True or false? Fusion in a main sequence star can make elements heavier than iron.
False. Fusion in stars makes elements up to iron; heavier elements need a supernova.
Name, in order, the stages in the life cycle of a star about the size of the Sun.
Nebula → protostar → main sequence star → red giant → white dwarf → black dwarf.
What stage follows the main sequence for a star the size of the Sun?
It expands to become a red giant.
What happens to a red giant of about the Sun's mass at the end of that stage?
It collapses (outer layers ejected) to become a white dwarf.
What is a black dwarf?
A white dwarf that has cooled down so much that it no longer emits visible light.
True or false? The Sun will end its life cycle as a supernova.
False. It is not massive enough; it will become a red giant, then a white dwarf, then a black dwarf.
Name, in order, the stages in the life cycle of a star much more massive than the Sun.
Nebula → protostar → main sequence star → red supergiant → supernova → neutron star or black hole.
What is a supernova?
The huge explosion of a massive star at the end of its red supergiant stage.
What decides whether a supernova leaves behind a neutron star or a black hole?
The mass of the star — the most massive stars form black holes.
What determines the life cycle a star will follow?
Its size (mass).
Which stages are the same for a Sun-sized star and a much more massive star?
Nebula, protostar and main sequence star — the life cycles differ only after the main sequence.
True or false? Every massive star ends its life as a black hole.
False. A supernova leaves either a neutron star or, for the most massive stars, a black hole.
What force keeps planets, moons and artificial satellites in their orbits?
Gravity (the gravitational force of attraction).
What is an artificial satellite?
A man-made object placed in orbit around a planet, e.g. the Hubble Space Telescope.
What is the difference between a planet and a moon?
Planets orbit the Sun; moons (natural satellites) orbit planets.
In a circular orbit, in which direction does the gravitational force on the orbiting body act?
Towards the centre of the orbit — towards the body it orbits.
For a body in a circular orbit, what happens to its velocity and its speed?
The velocity changes because the direction of motion keeps changing, but the speed stays constant.
True or false? A satellite moving in a circular orbit at constant speed is accelerating.
True. Gravity makes it accelerate towards the planet, changing its direction and so its velocity.
For a stable orbit, what must change if the orbital speed changes?
The radius of the orbit.
If a satellite is to orbit stably at a faster speed, what must happen to its orbital radius?
It must decrease — faster stable orbits have smaller radii.
How does the speed of a satellite in a stable orbit compare when the orbital radius is larger?
It is slower — the larger the radius, the slower the orbital speed.
True or false? A satellite in a higher stable orbit travels faster than one in a lower stable orbit.
False. A larger orbital radius means a slower orbital speed.