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Flashcards · 8463 · Topic 8

Space physics flashcards

15 cards on Topic 8, subtopics 4.8.1 to 4.8.2. Pick a subtopic or study them all.

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4.8.1 Solar system; stability of orbital motions; satellites

What is in our solar system?
One star (the Sun), eight planets, dwarf planets, and natural satellites (moons) that orbit planets. It is a small part of the Milky Way galaxy.
How did the Sun form and start to shine?
Gravity pulled a cloud of dust and gas (a nebula) together. It became hot and dense enough for nuclear fusion of light nuclei, which releases energy.
Why is a main sequence star stable?
The inward pull of gravity is balanced by the outward pressure from the energy released by fusion, so the star is in equilibrium.
Life cycle of a star about the size of the Sun
Nebula → protostar → main sequence star → red giant → white dwarf → black dwarf.
Life cycle of a star much more massive than the Sun
Nebula → protostar → main sequence star → red super giant → supernova → neutron star or black hole.
Where are elements heavier than iron produced?
In a supernova, which also distributes the elements throughout the universe. Fusion in stars makes elements up to iron.
What keeps planets and satellites in their orbits?
Gravity, which provides the force towards the centre of the orbit.
A satellite in a stable orbit changes speed. What must happen to its orbit?Higher
The radius must change: a faster speed needs a smaller orbit; a slower speed, a larger one.
Why is a body in a circular orbit accelerating, though its speed is constant?Higher
Its direction changes all the time, so its velocity changes. The resultant force (gravity) acts towards the centre.

4.8.2 Red-shift

Red-shift
The observed increase in the wavelength of light from most distant galaxies.
What pattern does red-shift show?
The further away a galaxy is, the faster it is moving away from us and the bigger its red-shift.
How does red-shift support the Big Bang theory?
Distant galaxies are moving away, faster the further they are, so the universe is expanding. Traced back, it must have begun from a very small region that was extremely hot and dense.
What have observations of supernovae since 1998 suggested?
Distant galaxies are receding ever faster: the expansion of the universe is accelerating.
Name two things about the universe that are still not understood.
Dark mass (dark matter) and dark energy.
A line at 500 nm in the lab is seen at 515 nm from a galaxy. Percentage increase in wavelength?
15 ÷ 500 × 100 = 3.0%

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