The solar system

The solar system consists of our nearest star (the Sun) and the eight planets which orbit around it, together with their moons, other small celestial bodies and a belt of asteroids, also there are 3 dwarf planets. The Sun is at the centre of our solar system. All other bodies in the Solar System orbit the Sun, most of them taking many years to do so.

Units of measure

The universe is so big that the typical units of measure that we use
on Earth to calculate distances (kilometers, miles,…) are too small.
Because of this we use:

Astronomical units (AU): It is equivalent to the average distance
from the Earth to the Sun. About 150 million km. Generally used to
measure distances within the Solar System.

Light year. Distances in space are so vast that they are measured in
light years – the distance that light travels in a year. Light travels at
a speed of roughly 300 000 km per second. A light year is therefore
about 9 500 000 000 000 km

Seasons

Seasons are caused by the Earth´s rotation around a tilted axix and the Earth´s revolution.

When the northern hemisphere is tilted towards the Sun it receives more solar energy than the southern hemisphere, it is summer in the northern hemisphere and winter in the Southern. The Summer solstice is the day with more daylight hours in the year, 21st of June.
As the Earth continues on its orbit at the Sun both hemispheres receive equal amount of sunlight. Days become longer in the southern hemisphere and shorter northern hemisphere, it is Autumn in the northern hemisphere. The two days in the year when the day and the night last the same are the equinoxes : 21st march, 22nd september.

Gravitation force:

The gravitational force of stars and planets depends on their mass. The greater the mass of an object, the greater the gravitational force that it exerts. The distance between two objects also affects their gravity: the further apart they are, the weaker the force.

Natural satallite

Is a solid rocky object that orbits a planet. The Earth has only one, but other planets can have over 20. These moons give out no light and are only visible when they reflect sunlight.

Asteroid

An asteroid is a rocky object wich is larger than a meteorid and smaller than a planet. Most are found in a belt between the orbits of Mars and Jupiter (it´s called: Asteroid belt)

Meteor

A meteor is a small body, such as rock or piece of dust moving throught space, they range of large rocks weighining several tons to small grains of dust. As they enter in the Atmosphere of a planet they heat up as a result of friction as they move throught the gases this can make them glow and gives them their nickname of chooting stars. 

Comet

Comets are bodys made up of gases, dust and ice crystals wich has a long luinous tail. They look like stars, but they orbit them.

Division of galaxies

Beyond our galaxi (The milky way) are many others galaxies. Based on their shape they are divided into espiral, elliptical and irregular.

- Elliptical: They are spherical shaped.

- Spiral: Our galaxy, the Milky Way is classified as one of these galaxies.

- Irregular galaxies.

Theorys about the universe.

 Claudius Ptolemy
(AD 100-165), a great Greek astronomer, argued that the stars and planets moved around the Earth in circles, because the circle was a perfect shape created by the gods. This is what scientist call the Geocentric theory. His description of how the universe worked was accepted for more than 1,500 years, when
Nicolas Copernicus (1473-1543) noticed that the movements of the Earth could be better explained if the Sun, not the Earth, lay at the centre. This is called the Heliocentric theory. Like Ptolemy, Copernicus believed that the planets moved in circles, but Johannes Kepler (1571-1630) showed that their orbits were elliptical (oval-shaped).

Planets

There are 8 planets in the solar system:

- Inner ones (Rocky planets):

Mercury, Venus, Earth and Mars.

- Outer ones (Gas giants)

Jupiter, Saturn, Uranus and Neptune.
But there are also some Darf planets:
(3) Pluto, Ceres and Eris.

Stars

A star is a masive ball of hot gas that gives off heat and light. Almost all stars are much larger than Earth. Our nearest star is the Sun, is 150 million km away.

Fact:Earth´s second nearest star, Alpha centauri C, is 4.21 light years away.

information founded in the book: Space (usborne discovery)