UNIT 6b
(Space Physics and Radioactivity)
The solar system
Solar system is a planetary system (a star and orbiting objects)
The Sun Mercury Venus Earth Mars asteroid belt Jupiter Saturn Uranus
Neptune Pluto
Earth’s moon Artificial Satellite
Dwarf planet
o The sun (our star), a hot sphere of gas.
o Planets (large objects which orbit a star), all orbit in the same plane and all
have slightly elliptical orbits.
o The time to complete 1 orbit increases with distance from the Sun.
o The inner planets are all terrestrial (rocky) planets.
o Outer planets (Jupiter…) are all gaseous giants. Small rocky core but are
mostly made of gases such as hydrogen and helium.
o Dwarf planets (e.g. Pluto), planet like objects that are too small to be
planets.
o Asteroid belt is made up of asteroids and 1 dwarf planet and is between
Mars and Jupiter. Asteroids are big pieces of rock and metal that orbit.
Moons and artificial satellites:
A satellite is anything that orbits a planet/dwarf planet – can be natural or
artificial (manmade)
o Moons – natural satellites, most planets have moons orbiting them. Some
of the inner planets have few moons, outer have many.
o TV Satellites – ISS (International Space Station) and Humble Space
Telescope all orbit Earth and are examples of artificial satellites (put into
orbit by humans).
Comets
o Comet – balls of rock, dust and ice which orbit the Sun in very elongated
ellipses (often different planes from the planets).
o They have very large orbits that can pass far beyond the solar system.
o As a comet approaches the Sun, the ice melts, leaving a bright tail of gas
and debris which can be millions of Km long.
,Sizes and distances in space
The universe
The universe is made of billions of galaxies. Galaxies are made up of billions of
stars and planets. Our planetary system is the Solar System which is one of
billions which form the Milky Way galaxy.
The Sun is roughly halfway along one of the spiral arms of the Milky Way. The
observable universe is the part which we can detect from Earth.
Sizes
Planets – a few hundred thousand km. Earth – 13,000 km.
Stars – a few hundred thousand km to several billion km.
Planetary systems – bigger than stars (includes all that orbits it too). The Solar
System is 1000’s of times bigger than the Sun).
Galaxies – contain billions of stars – much bigger than planetary systems.
Distances in space
In a vacuum, all electromagnetic waves travel at the speed of light. (roughly 3 x
108 m/s).
A light year is the distance that electromagnetic waves travel in 1 yr. so if
a star is 5 light years from earth it would take 5 years at the speed of light
to get there.
To convert between light years and metres, find the distance in metres
that light travels in 1 year using s = d/t . ‘s’ is the speed of light (m/s), and
‘t’ is time (seconds). Then multiply distance by n. of light years.
, As well as light years, shorter distances are measured in light minutes and
light seconds.
The Astronomical Unit (Au) is used for distances. 1 Au = average dist. from
Earth to Sun
(Space Physics and Radioactivity)
The solar system
Solar system is a planetary system (a star and orbiting objects)
The Sun Mercury Venus Earth Mars asteroid belt Jupiter Saturn Uranus
Neptune Pluto
Earth’s moon Artificial Satellite
Dwarf planet
o The sun (our star), a hot sphere of gas.
o Planets (large objects which orbit a star), all orbit in the same plane and all
have slightly elliptical orbits.
o The time to complete 1 orbit increases with distance from the Sun.
o The inner planets are all terrestrial (rocky) planets.
o Outer planets (Jupiter…) are all gaseous giants. Small rocky core but are
mostly made of gases such as hydrogen and helium.
o Dwarf planets (e.g. Pluto), planet like objects that are too small to be
planets.
o Asteroid belt is made up of asteroids and 1 dwarf planet and is between
Mars and Jupiter. Asteroids are big pieces of rock and metal that orbit.
Moons and artificial satellites:
A satellite is anything that orbits a planet/dwarf planet – can be natural or
artificial (manmade)
o Moons – natural satellites, most planets have moons orbiting them. Some
of the inner planets have few moons, outer have many.
o TV Satellites – ISS (International Space Station) and Humble Space
Telescope all orbit Earth and are examples of artificial satellites (put into
orbit by humans).
Comets
o Comet – balls of rock, dust and ice which orbit the Sun in very elongated
ellipses (often different planes from the planets).
o They have very large orbits that can pass far beyond the solar system.
o As a comet approaches the Sun, the ice melts, leaving a bright tail of gas
and debris which can be millions of Km long.
,Sizes and distances in space
The universe
The universe is made of billions of galaxies. Galaxies are made up of billions of
stars and planets. Our planetary system is the Solar System which is one of
billions which form the Milky Way galaxy.
The Sun is roughly halfway along one of the spiral arms of the Milky Way. The
observable universe is the part which we can detect from Earth.
Sizes
Planets – a few hundred thousand km. Earth – 13,000 km.
Stars – a few hundred thousand km to several billion km.
Planetary systems – bigger than stars (includes all that orbits it too). The Solar
System is 1000’s of times bigger than the Sun).
Galaxies – contain billions of stars – much bigger than planetary systems.
Distances in space
In a vacuum, all electromagnetic waves travel at the speed of light. (roughly 3 x
108 m/s).
A light year is the distance that electromagnetic waves travel in 1 yr. so if
a star is 5 light years from earth it would take 5 years at the speed of light
to get there.
To convert between light years and metres, find the distance in metres
that light travels in 1 year using s = d/t . ‘s’ is the speed of light (m/s), and
‘t’ is time (seconds). Then multiply distance by n. of light years.
, As well as light years, shorter distances are measured in light minutes and
light seconds.
The Astronomical Unit (Au) is used for distances. 1 Au = average dist. from
Earth to Sun
