Chapter 1 Cosmology and the Birth of Earth
1.2 An image of our Universe
Structure of the Universe
The Universe is the space and everything it contains. It contains matter (substance that makes up
objects) and energy (the ability to do work). We can refer to the amount of matter in an object as mass.
In the Western world two distinct schools developed concerning the arrangement of stars and planets,
and their relationship to the Earth, Sun and moon.
1) Geocentric model = Earth in the middle (without moving) and planets, sun and stars moving around
it in circular orbits.
2) Heliocentric model= Sun at the centre and other planets and stars orbiting around the Sun.
In the renaissance, Copernicus and Galilei proved that the Earth and planets did orbit the Sun. Keppler
discovered that the planets follow elliptical orbits (instead of circular). And Isaac Newton explained
gravity, which made it possible to understand why planets orbit a star.
A star is an immense sphere of incandescent 1 gas that emits intense energy. (Sun=star)
A planet is an object that orbits a star, is roughly spherical and has cleared it’s
neighborhood of other objects (gravity has pulled all particles in the orbit to the planet)
A moon is a sizable body orbiting a planet
A asteroid is a rocky and/or metallic object with diameters ranging from 1 cm to about
930 km. Icy (materials that could exist in gas form under conditions of the Earth, but
which are solid) bodies with diameters over 2 km are called dwarf planets
A comet is an icy object on path to the inner part of the Solar system (by gravitational
pull of planets) where they release long tails 2of gas.
The gravitational pull holds on to many objects which together with the Sun are called the Solar
system. All planets orbit in the same direction and plane 3 called ecliptic.
* The inner planets (Mercury, Venus, Earth, Mars) are called terrestrial planets. They are small, consist
of a shell of rock surrounding a ball of metal.
*The outer planets (Jupiter, Saturn, Uranus, Neptune) are known as giant or Jovian planets. These are
very big and exist of a little bit of rock/metal and a lot of gas.
1 Incandescent = gloeiend
2 Tail= staart
3 Plane=schijf
, Dimensions of the Earth
The first person who came to a good estimate of the dimensions of the Earth, was the
Greek astronomer Erastosthenes. He saw that in
Syene, the Sun lit the base of a deep vertical well
precisely at noon. And if the Earth would be
spherical, it couldn’t be the same at another place at
the same time. So he measured the shadow of a vertical
building in Alexandria. And he calculated that the perimeter of the
Earth was 39,400 km.
Speed of light
Since researchers discovered that light travels at a constant speed of
about 300,000 km per second in space, they
use it to describe huge distances between objects in
space. They define a large distance by
stating how long it takes for light to travel
the distance. A light year is the distance light travels
in one Earth year.
Motion of the Earth
Earth rotates on its axis, the imaginary line that
passes through the center of the Earth and pierces the
planet’s surface at its two poles. Earth’s axis
currently tilts at about 23,4 degree relative to the
ecliptic. The Earth rotates once in about 24 hours
with respect to the sun and once every 23 hours 56
minutes and 4 seconds with respect to the stars.
The Earth also orbits the Sun, traveling counterclockwise. It takes one year to complete. This causes
the seasons.
1.3 Forming the Universe
Doppler Effect
(sound)
When sound waves pass, air moves back and forth, alternately compressing and expanding. We refer
to the distance between waves as the wavelength and the number of waves that pass a point in a given
time interval as the frequency.
When a train moves towards you, the sound waves get compressed by the train. So the wave length is
smaller and the frequency is higher. When the train passed you, the sound waves get expanded. So the
wave length is bigger and the frequency is lower. This, the change in frequency that happens when a
wave source moves, is known as the Doppler effect.
(light)
The Doppler effect also applies to light, but can be noticed only if the light source moves very fast.
The color you see depends on the frequency of the light waves. Red light has a longer wavelength
(lower frequency) than does blue light (higher frequency, shorter wavelength).
1.2 An image of our Universe
Structure of the Universe
The Universe is the space and everything it contains. It contains matter (substance that makes up
objects) and energy (the ability to do work). We can refer to the amount of matter in an object as mass.
In the Western world two distinct schools developed concerning the arrangement of stars and planets,
and their relationship to the Earth, Sun and moon.
1) Geocentric model = Earth in the middle (without moving) and planets, sun and stars moving around
it in circular orbits.
2) Heliocentric model= Sun at the centre and other planets and stars orbiting around the Sun.
In the renaissance, Copernicus and Galilei proved that the Earth and planets did orbit the Sun. Keppler
discovered that the planets follow elliptical orbits (instead of circular). And Isaac Newton explained
gravity, which made it possible to understand why planets orbit a star.
A star is an immense sphere of incandescent 1 gas that emits intense energy. (Sun=star)
A planet is an object that orbits a star, is roughly spherical and has cleared it’s
neighborhood of other objects (gravity has pulled all particles in the orbit to the planet)
A moon is a sizable body orbiting a planet
A asteroid is a rocky and/or metallic object with diameters ranging from 1 cm to about
930 km. Icy (materials that could exist in gas form under conditions of the Earth, but
which are solid) bodies with diameters over 2 km are called dwarf planets
A comet is an icy object on path to the inner part of the Solar system (by gravitational
pull of planets) where they release long tails 2of gas.
The gravitational pull holds on to many objects which together with the Sun are called the Solar
system. All planets orbit in the same direction and plane 3 called ecliptic.
* The inner planets (Mercury, Venus, Earth, Mars) are called terrestrial planets. They are small, consist
of a shell of rock surrounding a ball of metal.
*The outer planets (Jupiter, Saturn, Uranus, Neptune) are known as giant or Jovian planets. These are
very big and exist of a little bit of rock/metal and a lot of gas.
1 Incandescent = gloeiend
2 Tail= staart
3 Plane=schijf
, Dimensions of the Earth
The first person who came to a good estimate of the dimensions of the Earth, was the
Greek astronomer Erastosthenes. He saw that in
Syene, the Sun lit the base of a deep vertical well
precisely at noon. And if the Earth would be
spherical, it couldn’t be the same at another place at
the same time. So he measured the shadow of a vertical
building in Alexandria. And he calculated that the perimeter of the
Earth was 39,400 km.
Speed of light
Since researchers discovered that light travels at a constant speed of
about 300,000 km per second in space, they
use it to describe huge distances between objects in
space. They define a large distance by
stating how long it takes for light to travel
the distance. A light year is the distance light travels
in one Earth year.
Motion of the Earth
Earth rotates on its axis, the imaginary line that
passes through the center of the Earth and pierces the
planet’s surface at its two poles. Earth’s axis
currently tilts at about 23,4 degree relative to the
ecliptic. The Earth rotates once in about 24 hours
with respect to the sun and once every 23 hours 56
minutes and 4 seconds with respect to the stars.
The Earth also orbits the Sun, traveling counterclockwise. It takes one year to complete. This causes
the seasons.
1.3 Forming the Universe
Doppler Effect
(sound)
When sound waves pass, air moves back and forth, alternately compressing and expanding. We refer
to the distance between waves as the wavelength and the number of waves that pass a point in a given
time interval as the frequency.
When a train moves towards you, the sound waves get compressed by the train. So the wave length is
smaller and the frequency is higher. When the train passed you, the sound waves get expanded. So the
wave length is bigger and the frequency is lower. This, the change in frequency that happens when a
wave source moves, is known as the Doppler effect.
(light)
The Doppler effect also applies to light, but can be noticed only if the light source moves very fast.
The color you see depends on the frequency of the light waves. Red light has a longer wavelength
(lower frequency) than does blue light (higher frequency, shorter wavelength).
