The Solar System - our celestial neighbourhood
The Sun and its family of planets, moons, asteroids and comets is at
present the only solar system we know. When you look at the sky at night, most of those "little lights" you see are stars - distant
suns. Our Sun is just one of many billions of stars in the Milky Way galaxy. Planets have only actually been discovered orbiting a
few hundreds of these stars (including a
5.5 "Earth-mass" one by
Perth Observatory astronomers. These discoveries depend on detecting
anomalies in stellar motion or gravitational
microlensing, as may be caused
by a planet, or by spectral analysis), although many (probably about a quarter) of all stars are believed have planetary systems like ours.
So few have been found because planets are small and don't give off their own light - they only reflect light from their parent star.
Even the world's largest telescopes couldn't directly image planets, if there were any, orbiting the nearest stars. However, the Hubble Space
Telescope has recently made some observations that appear to show a planet orbiting around a star - but not with any great clarity.
The Solar System has a well-defined layout: the Sun in the centre, then
- in order - Mercury, Venus, Earth, Mars, the asteroid belt, Jupiter,
Saturn, Uranus and Neptune. Next come trans-Neptunian Objects and
comets come from even further out. (Pluto was
classified in 2006 August by the International Astronomical Union
to the status of dwarf planet. As well
as re-classifying Pluto, the International Astronomical Union has
created a definition of the term planet and
instigated a new name for small Solar System bodies
(SSSBs);
objects that are neither planets nor dwarf planets.) You can make
up a mnemonic (a code) to remember the order of the
EIGHT planets.
For instance: My Very Elegant Mother Just Sang Until November!
Solar System Fact Sheets
Additional Astronomy Fact Sheets
The first four planets, Mercury, Venus, Earth, and
Mars, are relatively small and rocky. They are called the terrestrial
planets. Out beyond the asteroid belt, the planets are quite different
- big, light, and gaseous - the giant gas planets: Jupiter, Saturn,
Uranus, and Neptune. Pluto seems to be different again - small and
icy and is probably a large representative of trans-Neptunian objects.
Spacecraft couldn't land on the giant gas planets; there's no solid surface.
But the giant planets have plenty of moons, and the moons are solid. So
if people travel to Jupiter in the future, they could land on - for example
- the moon Ganymede.
From watching movies such as "Star Wars", you could easily come to believe
that Earth people are zooming all over the universe. In fact, only
a small number of astronauts - all of them Americans - have traveled away
from Earth into space: the Apollo program from late 1968 to mid 1972 sent
a total of eight craft to the Moon. Six of these,
Apollo 11, 12, 14, 15,
16, and 17, landed pairs of astronauts on the Moon. All the other manned
space-flights since then have simply been into orbit around the Earth (e.g.
Skylab, Soyuz, Mir, the Space Shuttle and the International Space Station).
Recently, China became the third country, after the USA and the USSR, able to send
human beings into space. Both China and the USA are planning to send astronauts to the
Moon again, but probably not for a decade or more.
While many probes have landed on Venus and Mars, only one space probe – Voyager 2 –
has visited the two furthest planets; it flew by Uranus in 1986 and Neptune in 1989. On the 12th February 2001,
the NEAR Shoemaker spacecraft landed on asteroid 433 Eros. No probe has yet been to Pluto, but the
New Horizons spacecraft is due there in 2015.
Information for Teachers
This resource addresses many CURRICULUM FRAMEWORK Science Learning Outcomes,
for all learning development phases, associated with the 'Earth And Beyond' concept.
