6. Space physics (24, 25) Flashcards
Explain:
observations of the apparent daily motion of the Sun and periodic cycle of day and night
periodic nature of the seasons
periodic nature of the Moon’s cycle of phases
Earth is a planet that rotates on its axis, which is tilted, once in approximately 24 hours.
sunrise- eastern horizon. midday- overhead. sunset- western horizon.
seasons occur because of tilt of earth’s axis. northern hemisphere is tipped away from sun so energy from sun’s rays is more spread out- colder- fewer hours of sunlight-winter. northern hemisphere tipped towards the sun- receives longer hours of sunlight- summer. no seasons experiences at equator as sun’s rays always hit at same angle
moon orbits earth every 27.5 days. reflects sun- different parts illuminated by sun so there are phases.
Define average orbital speed
v = 2π r/T
r is the average radius of the orbit and T is the orbital period
Describe the Solar System as containing
(a) one star, the Sun
(b) the eight named planets and MVEMJSUN
(c) minor planets that orbit the Sun, including dwarf planets such as Pluto and asteroids in the asteroid belt
(d) moons, that orbit the planets
(e) smaller Solar System bodies, including comets and natural satellites
the four planets nearest the Sun & the four planets furthest from the Sun—
the four planets nearest the Sun are rocky and small and
the four planets furthest from the Sun are gaseous and large
(a) the model’s dependence on gravity
(b) the presence of many elements in interstellar clouds of gas and dust
(c) the rotation of material in the cloud and the formation of an accretion disc
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
Sun
contains
force that keeps an object in orbit
distance from sun of planets affects strength and speed
the Sun contains most of the mass of the Solar System and this explains why the planets orbit the Sun
the force that keeps an object in orbit around the Sun is the gravitational attraction of the Sun
the strength of the Sun’s gravitational field and the orbital speeds of the planets decrease as the distance from the Sun increases (but greater mass more strength)
an object in an elliptical orbit travels faster when closer to the Sun and explain this using the conservation of energy- (near sun- min gpe max ke and moving fastest because gravitational force of sun acts and pulls causing it to accelerate and ke carries it to furthest point of orbit where object slows down and is pulled in towards sun again). (planets, minor planets and comets have elliptical orbits, and the Sun is not at the centre of the elliptical orbit, except when the orbit is approximately circular).
Analyse and interpret planetary data about orbital distance, orbital duration, density, surface temperature and uniform gravitational field strength at the planet’s surface—
Describe sun & how stars are powered
Sun is a star of medium size, consisting mostly of hydrogen and helium, and it radiates most of its energy in the infrared, visible and ultraviolet regions of the electromagnetic spectrum
stars are powered by nuclear reactions that release energy and that in stable stars the nuclear reactions involve the fusion of hydrogen into helium
Stars:
galaxies
sun
other stars
astronomical distances
(a) galaxies are each made up of many billions of stars
(b) the Sun is a star in the galaxy known as the Milky Way
(c) other stars that make up the Milky Way are much further away from the Earth than the Sun is from the Earth
(d) astronomical distances can be measured in light-years, where one light-year is the distance travelled in (the vacuum of) space by light in one year
one light-year
one light-year is equal to 9.5 × 10^15m
Describe the life cycle of a star
(a) a star is formed from interstellar clouds of gas and dust that contain hydrogen
(b) a protostar is an interstellar cloud collapsing and increasing in temperature as a result of its internal gravitational attraction
(c) a protostar becomes a stable star when the inward force of gravitational attraction is balanced by an outward force due to the high temperature in the centre of the star
(d) all stars eventually run out of hydrogen as fuel for the nuclear reaction
(e) most stars expand to form red giants and more massive stars expand to form red supergiants when most of the hydrogen in the centre of the star has been converted to helium
(f) a red giant from a less massive star forms a planetary nebula with a white dwarf star at its centre
(g) a red supergiant explodes as a supernova, forming a nebula containing hydrogen and new heavier elements, leaving behind a neutron star or a black hole at its centre
(h) the nebula from a supernova may form new stars with orbiting planets
Describe Milky Way and state its diameter
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
Describe redshift
an increase in the observed wavelength of electromagnetic radiation emitted from receding stars and galaxies- (wavelength (of light from distant galaxies) increases occurs when galaxies are moving away (from Earth)
the light emitted from distant galaxies appears redshifted in comparison with light emitted on the Earth
redshift in the light from distant galaxies is evidence that the Universe is expanding and supports the Big Bang Theory
Describe CMBR
microwave radiation of a specific frequency is observed at all points in space around us and is known as cosmic microwave background radiation (CMBR)
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
How can the following be found:
the speed v at which a galaxy is moving away from the Earth
the distance of a far galaxy d
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
the distance of a far galaxy d can be determined using the brightness of a supernova in that galaxy
