Flashcards · 5054 · Topic 6

Space physics flashcards

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

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Earth and Moon: rotation, orbit periods, and Sun–Earth light time: Earth rotates once in about 24 hours and orbits the Sun in about 365 days (an ellipse, nearly circular). The Moon orbits the Earth in about one month. Sunlight takes about 500 s to reach us.
Average orbital speed equation: v = 2πr/T, where r is the average orbit radius and T the orbital period (in seconds). Rearranged: r = vT/2π, T = 2πr/v.
A body orbits at r = 2.0 × 10⁸ km in 300 days. Average orbital speed?: T = 300 × 24 × 3600 = 2.59 × 10⁷ s. v = 2π × 2.0 × 10⁸ ÷ 2.59 × 10⁷ = 48 km/s.
Members of the Solar System, and the planets in order: The Sun, eight planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune), minor planets (dwarf planets such as Pluto, asteroids), moons, and smaller bodies such as comets.
What does gravitational field strength depend on in the Solar System?: At a planet's surface: the planet's mass. Around a planet: it decreases with distance. The Sun's surface field is greater than any planet's.
What keeps planets in orbit, and how does orbital speed change with distance from the Sun?: The gravitational attraction of the Sun, acting towards the Sun. Further from the Sun its field is weaker and the orbital speed is lower.

The Sun as a star: A medium-sized star, mostly hydrogen and helium. Radiates most energy as infrared, visible and ultraviolet. Powered by fusion of hydrogen into helium.
Galaxy, Milky Way and light-year: A galaxy is many billions of stars; the Milky Way contains the Sun and is about 100 000 light-years across. A light-year is the distance light travels in a vacuum in one year (a distance, not a time).
How does a protostar become a stable star?: The protostar collapses and warms under its own gravity. It is stable when the inward gravitational force is balanced by an outward force from the high temperature at its centre.
End points of less massive and more massive stars: Less massive: red giant → planetary nebula and white dwarf. More massive: red supergiant → supernova → nebula with heavier elements, leaving a neutron star or black hole.
Redshift. Galaxy X has a larger redshift than galaxy Y: compare them.: Redshift: an increase in the observed wavelength of radiation from receding galaxies. X is further away and moving away faster than Y.
How does redshift support the Big Bang?: Light from distant galaxies is redshifted, so they are receding and the Universe is expanding. Reversing the expansion, everything started close together.