Space Physics
Map Your Gaps
Card 1 of 10
Swipe right if you know it, left if you don't
✔ Know
✖ Don't know
The Solar System
Our solar system contains several types of object, all orbiting the Sun due to gravity.
Naming the types of object in the solar system is the starting point for this topic.
The Solar System — Key Knowledge
- Sun the star at the centre of our solar system
- Planets eight — Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
- Dwarf planets e.g. Pluto — orbit the Sun but haven't cleared their orbital path
- Moons natural satellites that orbit planets
- Asteroids small rocky bodies, mostly between Mars and Jupiter
- Comets icy bodies with elongated orbits — develop tails when near the Sun
Stars and Planets
Stars and planets are fundamentally different objects.
The Sun is a star; Earth is a planet that reflects its light.
Stars and Planets — Key Knowledge
- Stars produce their own light and energy through nuclear fusion
- Planets do not produce light — they reflect light from their star
Scale of the Universe
Objects in space vary enormously in size, from planets up to the entire universe.
Size order: planet < star < galaxy < universe.
Scale of the Universe — Key Knowledge
- Planet smallest scale
- Star much larger than planets
- Galaxy a collection of billions of stars — ours is the Milky Way
- Universe contains billions of galaxies — the largest scale
Orbits and Gravity
Objects in orbit are held in place by gravitational attraction, which provides the centripetal force needed for circular motion.
Without gravity, an orbiting object would fly off in a straight line.
Orbits and Gravity — Key Knowledge
- Gravity the force that keeps planets, moons and satellites in orbit
- Centripetal force gravity acts as the centripetal force — pulling the orbiting object toward the centre
Orbital Speed and Radius
For a stable orbit, there is a link between orbital speed and distance from the body being orbited.
Mercury orbits much faster than Neptune because it is closer to the Sun.
Orbital Speed and Radius — Key Knowledge
- Closer orbits require higher speed — stronger gravitational pull closer to the central body
- Further orbits lower speed — weaker gravitational pull at greater distance
Satellites
A satellite is any object that orbits a larger body. They can be natural or artificial.
Both natural and artificial satellites are kept in orbit by gravity.
Satellites — Key Knowledge
- Natural satellites moons — e.g. the Moon orbiting Earth
- Artificial satellites man-made objects placed in orbit — used for communications, GPS, weather monitoring
Red-shift
Light from distant galaxies is shifted toward the red end of the spectrum — this is called red-shift.
Red-shift is observed in light from galaxies — it tells us about their motion relative to us.
Red-shift — Key Knowledge
- Red-shift increase in wavelength of light from a galaxy moving away from us
- Greater distance further galaxies show greater red-shift
- Greater speed greater red-shift means the galaxy is moving away faster
The Expanding Universe
Red-shift observations show that distant galaxies are all moving away from us, and from each other — the universe is expanding.
The expansion is of space itself, not objects moving through space.
The Expanding Universe — Key Knowledge
- Expanding universe all distant galaxies are moving apart — space itself is stretching
- Hubble's observation further galaxies recede faster — consistent with expansion from a single point
The Big Bang Theory
If the universe is expanding, it must have been smaller and denser in the past. The Big Bang theory states the universe began from a very small, very hot, very dense point and has been expanding ever since.
The Big Bang was not an explosion in space — it was the rapid expansion of space itself.
The Big Bang Theory — Key Knowledge
- Big Bang the universe began approximately 13.8 billion years ago from an incredibly hot, dense point
Cosmic Microwave Background Radiation
CMBR is low-frequency electromagnetic radiation detected from all directions in space. It is the leftover thermal radiation from the early universe.
Red-shift and CMBR together provide the two main pieces of evidence for the Big Bang theory.
Cosmic Microwave Background Radiation — Key Knowledge
- CMBR cosmic microwave background radiation — detected uniformly in all directions
- Evidence for the Big Bang CMBR is consistent with the predicted cooling of radiation from the hot, dense early universe