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Chapter 1: Cosmology
Cosmology and the Birth of the Earth
1.1 Introduction
In the context of scientific cosmology, the Universe contains of 2 basic entities:
Matter: the material substance of the universe, it consists of atoms and has mass.
Energy: the capacity to do work.
1.2 An Image of Our Universe
Geocentric model = an ancient Greek idea suggesting that the Earth sat motionless in the center of the Universe while stars and
other planets and the Sun orbited around it.
Heliocentric model = the idea that all heavenly objected including the Earth orbited the Sun.
🌍 Planet = An object that orbits a star, is roughly spherical and has
cleared its neighbourhood of other objects. (three properties)
→ exoplanet = planet that orbits around other stars
Over time, stars appear to Wanderer = planēs in Greek. That’s where the word planet comes from.
Over time, planets appear to
revolve around in circles.
wander (retrograde motion).
Chapter 1: Cosmology 1
, terrestrial planets = planets that are of
The Earth is located in the Solar System
Mercury, Venus, Earth and Mars comparable size and character to the Earth and and orbits around a star called the Sun. Our
(the inner planets) consist of a metallic core surrounded by a rock Sun is one of over 300 billion stars in the
mantle Milky Way Galaxy. There are billions of
giant planets (jovian planets) → Jupiter and galaxies in the universe.
Jupiter, Saturn, Uranus and
Saturn are called gas giants → Uranus and
Neptune (the outer planets)
Neptune are called ice giants
Other objects in the solar system:
Moons A sizeable solid body, locked in orbit around a planet.
A relatively small rocky or metallic object that orbits the Sun, most lie between the orbits of Mars and Jupiter.
Asteroids
Known asteroids can range in diameter from 1 cm to 930 km
Icy bodies lying outside the orbit of Neptune, those that occur in a donut-like ring form the Kuiper Belt and more
Kuiper Belt and Oort Cloud Objects
distant ones form the Oort Cloud Objects. They can range in diameter from less than 1 cm to 2000 km
An asteroid with a diameter greater than about 900 km that has not cleared its orbit of debris. The only five
Dwarf Planets
identified dwarf planets are: Pluto, Eris, Haumea, Ceres and Makemake
Comets Kuiper Belt or Oort Cloud Objects that follow an elliptical orbit that brings them into the inner Solar System.
How was the circumference of the earth calculated?
The Greek astronomer Eratosthenes (ca. 276-194 BC) was the first to
come up with a good estimate. He compared the angle of the light from
the Sun on Earth in two different places; Alexandria and Syene. By using
the distance between the places (≈5000 stadia), he estimated that the
circumference of the Earth was 250,000 stadia ≈ 39,300 km. This is very
close to today’s value of 40,008 km.
💡 Light-year = the distance that light travels in one (Earth) year,
which is about 9.5 trillion kilometers.
The nearest star to Earth is called Alpha Centauri and lies about 40.85
trillion km or 4.37 light-years away. This means that the light we see
from the star when we look at the sky, left the star 4.37 years ago.
The Earth has proven motion in three ways: around its axis, around the
Sun and around the centre of the Milky Way.
1.3 Forming the Universe
Doppler Effect = a phenomenon in which the frequency of wave energy appears to change when a moving source of wave
energy passes an observer
→ A source of sound or light (which is a form of electromagnetic radiation) emits waves. When that source is moving towards an
observer it seems like the wavelength becomes shorter and therefore the frequency (= amount of waves per time interval) higher.
This is because the source has moved closer to the observer since the last wave was emitted.
Chapter 1: Cosmology 2
Chapter 1: Cosmology
Cosmology and the Birth of the Earth
1.1 Introduction
In the context of scientific cosmology, the Universe contains of 2 basic entities:
Matter: the material substance of the universe, it consists of atoms and has mass.
Energy: the capacity to do work.
1.2 An Image of Our Universe
Geocentric model = an ancient Greek idea suggesting that the Earth sat motionless in the center of the Universe while stars and
other planets and the Sun orbited around it.
Heliocentric model = the idea that all heavenly objected including the Earth orbited the Sun.
🌍 Planet = An object that orbits a star, is roughly spherical and has
cleared its neighbourhood of other objects. (three properties)
→ exoplanet = planet that orbits around other stars
Over time, stars appear to Wanderer = planēs in Greek. That’s where the word planet comes from.
Over time, planets appear to
revolve around in circles.
wander (retrograde motion).
Chapter 1: Cosmology 1
, terrestrial planets = planets that are of
The Earth is located in the Solar System
Mercury, Venus, Earth and Mars comparable size and character to the Earth and and orbits around a star called the Sun. Our
(the inner planets) consist of a metallic core surrounded by a rock Sun is one of over 300 billion stars in the
mantle Milky Way Galaxy. There are billions of
giant planets (jovian planets) → Jupiter and galaxies in the universe.
Jupiter, Saturn, Uranus and
Saturn are called gas giants → Uranus and
Neptune (the outer planets)
Neptune are called ice giants
Other objects in the solar system:
Moons A sizeable solid body, locked in orbit around a planet.
A relatively small rocky or metallic object that orbits the Sun, most lie between the orbits of Mars and Jupiter.
Asteroids
Known asteroids can range in diameter from 1 cm to 930 km
Icy bodies lying outside the orbit of Neptune, those that occur in a donut-like ring form the Kuiper Belt and more
Kuiper Belt and Oort Cloud Objects
distant ones form the Oort Cloud Objects. They can range in diameter from less than 1 cm to 2000 km
An asteroid with a diameter greater than about 900 km that has not cleared its orbit of debris. The only five
Dwarf Planets
identified dwarf planets are: Pluto, Eris, Haumea, Ceres and Makemake
Comets Kuiper Belt or Oort Cloud Objects that follow an elliptical orbit that brings them into the inner Solar System.
How was the circumference of the earth calculated?
The Greek astronomer Eratosthenes (ca. 276-194 BC) was the first to
come up with a good estimate. He compared the angle of the light from
the Sun on Earth in two different places; Alexandria and Syene. By using
the distance between the places (≈5000 stadia), he estimated that the
circumference of the Earth was 250,000 stadia ≈ 39,300 km. This is very
close to today’s value of 40,008 km.
💡 Light-year = the distance that light travels in one (Earth) year,
which is about 9.5 trillion kilometers.
The nearest star to Earth is called Alpha Centauri and lies about 40.85
trillion km or 4.37 light-years away. This means that the light we see
from the star when we look at the sky, left the star 4.37 years ago.
The Earth has proven motion in three ways: around its axis, around the
Sun and around the centre of the Milky Way.
1.3 Forming the Universe
Doppler Effect = a phenomenon in which the frequency of wave energy appears to change when a moving source of wave
energy passes an observer
→ A source of sound or light (which is a form of electromagnetic radiation) emits waves. When that source is moving towards an
observer it seems like the wavelength becomes shorter and therefore the frequency (= amount of waves per time interval) higher.
This is because the source has moved closer to the observer since the last wave was emitted.
Chapter 1: Cosmology 2
