Space physics

• the Earth is a planet that rotates on its axis, which is tilted, once in approximately 24 hours
• the Earth orbits the Sun once in approximately 365 days
• it takes approximately one month for the Moon to orbit the Earth
• the four planets nearest the Sun are rocky and small
• the four planets furthest from the Sun are gaseous and large
• planets, minor planets and comets have elliptical orbits
• the Sun is not at the centre of the elliptical orbit, except when the orbit is approximately circular
• 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
• 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
• the Sun contains most of the mass of the Solar System
• 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 decreases
• the orbital speeds of the planets decrease as the distance from the Sun increases
• an object in an elliptical orbit travels faster when closer to the Sun
• 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 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
• galaxies are each made up of many billions of stars
• the Sun is a star in the galaxy known as the Milky Way
• other stars that make up the Milky Way are much further away from the Earth than the Sun is from the Earth
• astronomical distances can be measured in light-years
• one light-year is the distance travelled in (the vacuum of) space by light in one year
• 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
• 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
• 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
• the life cycle of a 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
• the life cycle of a 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
• the life cycle of a 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
• the life cycle of a star: (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
• the life cycle of a star: (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
• the Milky Way is one of many billions of galaxies making up the Universe
• the diameter of the Milky Way is approximately 100000 light-years
• redshift is an increase in the observed wavelength of electromagnetic radiation emitted from receding stars and galaxies
• 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
• 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
• CMBR radiation has been expanded into the microwave region of the electromagnetic spectrum as the Universe expanded
• 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
• the Hubble constant is the ratio of the speed at which the galaxy is moving away from the Earth to its distance from the Earth