6. Space physics
- Syllabus
- 0625–2026–2027
- Section
- 6
- Level
- —
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In this section
Topic 6.1.1
6.1.1 The Earth
Objectives in this topic
6.1.1.1—Earth rotates on its tilted axis once
- Know the Earth rotates on its tilted axis once in about 24 hours; use this to explain the Sun’s apparent daily motion and the day/night cycle
6.1.1.2—Earth orbits the Sun once in
- Know: the Earth orbits the Sun once in approximately 365 days and use this to explain the periodic nature of the seasons
6.1.1.3—It takes approximately one month for
- Know: it takes approximately one month for the Moon to orbit the Earth and use this to explain the periodic nature of the Moon’s cycle of phases
6.1.1.4—Average orbital speed
- Define average orbital speed; recall/use: v = 2πr/T, where r is average orbital radius and T is orbital period
Topic 6.1.2
6.1.2 The Solar System
Objectives in this topic
6.1.2.1—Contents: (a) the Sun (one star) (b)
- Describe Solar System contents: (a) the Sun (one star) (b) eight named planets in order from the Sun (c) minor planets, including Pluto/dwarf planets and asteroid-belt asteroids (d) moons orbiting planets (e) smaller bodies, including comets and natural satellites
6.1.2.2—Four inner planets are small/rocky and
- Know the four inner planets are small/rocky and the four outer planets are large/gaseous; explain this with the accretion model: gravity, many elements in gas/dust clouds, rotating cloud material and accretion-disc formation
6.1.2.3—Strength of the gravitational field
- Know: the strength of the gravitational field (a) at the surface of a planet depends on the mass of the planet (b) around a planet decreases as the distance from the planet increases
6.1.2.4—Time it takes light to travel a
- Calculate the time it takes light to travel a significant distance such as between objects in the Solar System
6.1.2.5—Sun contains most of the mass of the
- Know: the Sun contains most of the mass of the Solar System and this explains why the planets orbit the Sun
6.1.2.6—Force that keeps an object in orbit
- Know: the force that keeps an object in orbit around the Sun is the gravitational attraction of the Sun
6.1.2.7—Planets, minor planets and comets have
- Know: planets, minor planets and comets have elliptical orbits, and recall that the Sun is not at the centre of the elliptical orbit, except when the orbit is approximately circular
6.1.2.8—Analyse and interpret planetary data
- Analyse and interpret planetary data about orbital distance, orbital duration, density, surface temperature and uniform gravitational field strength at the planet’s surface
6.1.2.9—Strength of the Sun’s gravitational
- Know: the strength of the Sun’s gravitational field decreases and that the orbital speeds of the planets decrease as the distance from the Sun increases
6.1.2.10—An object in an elliptical orbit
- Know: an object in an elliptical orbit travels faster when closer to the Sun and explain this using the conservation of energy
Topic 6.2.1
6.2.1 The Sun as a star
Objectives in this topic
6.2.1.1—Sun is a star of medium size
- Know: the Sun is a star of medium size, consisting mostly of hydrogen and helium, and that it radiates most of its energy in the infrared, visible light and ultraviolet regions of the electromagnetic spectrum
6.2.1.2—Stars are powered by nuclear reactions
- Know: stars are powered by nuclear reactions that release energy and that in stable stars the nuclear reactions involve the fusion of hydrogen into helium
Topic 6.2.2
6.2.2 Stars
Objectives in this topic
6.2.2.1—(a) galaxies contain many billions of
- State: (a) galaxies contain many billions of stars (b) the Sun is in the Milky Way (c) other Milky Way stars are much farther from Earth than the Sun (d) astronomical distances can use light-years: distance travelled by light in space in one year
6.2.2.2—One light-year is equal to 9.5 × 1015
- Know: one light-year is equal to 9.5 × 1015 m
6.2.2.3—Star life cycle: (a) forms from
- Describe a star life cycle: (a) forms from hydrogen-rich gas/dust clouds (b) protostar collapses under gravity and heats up (c) stable star forms when inward gravity balances outward pressure from high core temperature (d) stars eventually run out of hydrogen fuel (e) most expand to red giants; more massive stars become red supergiants after central hydrogen becomes helium (f) less massive red giant forms a planetary nebula with a white dwarf at the centre (g) red supergiant supernova forms a nebula with hydrogen/new heavier elements and leaves a neutron star or black hole (h) supernova nebula may form new stars with planets
Topic 6.2.3
6.2.3 The Universe
Objectives in this topic
6.2.3.1—Milky Way is one of many billions of
- Know: the Milky Way is one of many billions of galaxies making up the Universe and that the diameter of the Milky Way is approximately 100 000 light-years
6.2.3.2—Redshift as an increase in the
- Describe redshift as an increase in the observed wavelength of electromagnetic radiation emitted from receding stars and galaxies
6.2.3.3—Light emitted from distant galaxies
- Know: the light emitted from distant galaxies appears redshifted in comparison with light emitted on the Earth
6.2.3.4—Redshift in the light from distant
- Know: redshift in the light from distant galaxies is evidence that the Universe is expanding and supports the Big Bang Theory
6.2.3.5—Microwave radiation of a specific
- Know: microwave radiation of a specific frequency is observed at all points in space around us and is known as cosmic microwave background radiation (CMBR)
6.2.3.6—The CMBR was produced shortly after
- Explain that the CMBR was produced shortly after the Universe was formed and that this radiation has been expanded into the microwave region of the electromagnetic spectrum as the Universe expanded
6.2.3.7—Speed v at which a galaxy is moving
- Know: the speed v at which a galaxy is moving away from the Earth can be found from the change in wavelength of the galaxy’s starlight due to redshift
6.2.3.8—Distance d of a far galaxy can be
- Know: the distance d of a far galaxy can be determined using the brightness of a supernova in that galaxy
6.2.3.9—Hubble constant H0 as recession speed
- Define Hubble constant H0 as recession speed divided by distance from Earth; recall/use: H0 = v/d
6.2.3.10—Current estimate for H0 is 2.2 × 10–18
- Know: the current estimate for H0 is 2.2 × 10–18 per second
6.2.3.11—D/v = 1/H0 estimates the age of the
- Know d/v = 1/H0 estimates the age of the Universe and supports the idea that all matter was once at a single point