Skip to content
Marlbridge
Free trial

Flashcards · 0625 · Topic 6

Space physics flashcards

26 cards on Topic 6, subtopics 6.1 to 6.2. Pick a subtopic or study them all.

Study mode needs JavaScript. Every card is listed below, so you can still cover the answers and test yourself.

All 26 cards

For a quick read-through or printing. Cover the right-hand side to test yourself. Cards marked Extended are Extended (Supplement) content only.

6.1 The Earth and the Solar System

What causes day and night, and the Sun's apparent daily motion?
The Earth spins on its axis once in about 24 hours. The side facing the Sun has day. The Sun appears to rise in the east and set in the west because the Earth rotates.
What causes the seasons?
The Earth's axis is tilted. As it orbits the Sun (about 365 days), each hemisphere in turn leans towards the Sun and gets more energy per square metre. Not distance from the Sun.
What causes the phases of the Moon?
The Moon reflects sunlight. As it orbits the Earth (about one month) we see different amounts of its lit half. Not the Earth's shadow.
The eight planets in order from the Sun
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.
Members of the Solar System besides the Sun and planets
Minor planets (dwarf planets such as Pluto, asteroids in the asteroid belt), moons, and smaller bodies such as comets.
Why are the inner planets small and rocky and the outer ones large and gaseous?
Accretion model: near the young Sun it was hot, so only rock and metal stayed solid. Further out it was cold, so gas and ice were available and large cores pulled in gas.
Why do the planets orbit the Sun?
The Sun holds most of the Solar System's mass. Its gravitational attraction keeps the planets in orbit.
How long does light take to travel 1.5 × 10¹¹ m from the Sun to the Earth?
t = d/v = 1.5 × 10¹¹ ÷ 3.0 × 10⁸ = 500 s.
Shape of planetary and comet orbitsExtended
Elliptical. The Sun is not at the centre of the ellipse, except for a nearly circular orbit.
Where in its orbit is a comet fastest, and why?Extended
Nearest the Sun. As it moves towards the Sun it loses gravitational potential energy, which is transferred to kinetic energy.
Average orbital speed equation. Earth: r = 1.5 × 10¹¹ m, T = 3.15 × 10⁷ s.Extended
v = 2πr/T = 2π × 1.5 × 10¹¹ ÷ 3.15 × 10⁷ = 3.0 × 10⁴ m/s.
How do the Sun's field strength and orbital speed change for planets further from the Sun?Extended
The gravitational field is weaker further out, and the planets orbit more slowly.

6.2 Stars and the Universe

The Sun as a star
A medium-sized star, mostly hydrogen and helium. It radiates most of its energy as infrared, visible light and ultraviolet.
Galaxy, and the size of the Milky Way
A galaxy is made of many billions of stars. The Sun is in the Milky Way, which is about 100 000 light-years across.
Light-year
The distance light travels through space in one year. It is a distance, not a time.
Value of one light-year in metresExtended
9.5 × 10¹⁵ m.
Redshift
An increase in the observed wavelength of electromagnetic radiation from receding stars and galaxies.
What does redshift from distant galaxies show?
The galaxies are moving away, so the Universe is expanding. This supports the Big Bang Theory.
What powers a stable star like the Sun?Extended
Nuclear fusion of hydrogen into helium.
Life cycle of a star from cloud to stable starExtended
Interstellar cloud of gas and dust → gravity pulls it together and it heats up → protostar → stable star, when inward gravity is balanced by the outward force from the high core temperature.
End of a less massive star (like the Sun)Extended
When its core hydrogen is mostly used up it becomes a red giant, then forms a planetary nebula with a white dwarf at its centre.
End of a more massive starExtended
Red supergiant → supernova → a nebula of hydrogen and heavier elements, leaving a neutron star or a black hole. The nebula may form new stars with planets.
Cosmic microwave background radiation (CMBR)Extended
Microwave radiation of a specific frequency observed at all points in space. It was produced shortly after the Universe formed and was expanded into the microwave region as the Universe expanded.
Hubble constant: equation, value and what 1/H₀ estimatesExtended
H₀ = v/d (recession speed ÷ distance) ≈ 2.2 × 10⁻¹⁸ per second. 1/H₀ estimates the age of the Universe.
How are a distant galaxy's recession speed and distance found?Extended
Speed: from the change in wavelength (redshift) of its light. Distance: from the brightness of a supernova in it.
A galaxy recedes at 4.4 × 10⁶ m/s. Using H₀ = 2.2 × 10⁻¹⁸ /s, how far away is it?Extended
d = v/H₀ = 4.4 × 10⁶ ÷ 2.2 × 10⁻¹⁸ = 2.0 × 10²⁴ m.

Revise Space physics further