the universe topic

Early Ideas about the Universe

Ancient Beliefs and Mythology

• Early civilizations used celestial objects for predictions and timekeeping

• Ancient societies explained celestial phenomena through stories and myths

• Yolngu people: Story of Walu the Sun-woman

• Ancient Egyptians: Sun as the eye or body of Ra

Greek Contributions

• Homer (700 BCE): Believed Earth was flat

• Pythagoras (500 BCE): Proposed Earth and celestial bodies as spheres

• Aristotle (384-322 BCE): Geocentric model

• Aristarchus (310-230 BCE): Proposed heliocentric model (rejected at the time)

Problems with Early Models

1. Star positions drifted over time

2. Planetary movements were difficult to explain

Ptolemy's Model (100-170 CE)

• Added epicycles, deferents, and equants to Aristotle's model

• Improved predictions but lacked a proper mechanism

Renaissance Advancements

• Nicolaus Copernicus (1473-1543): Proposed heliocentric model

• Tycho Brahe: Improved observational techniques and instruments

• Observed a new star in 1572

• Proved comets moved among planets, disproving celestial spheres

Scientific Revolution

• Galileo Galilei (1564-1642): First astronomical telescope observations

  • Discovered Venus phases, Jupiter's moons, and Moon's surface features

• Johannes Kepler (1571-1630): Laws of planetary motion

  • Explained Mars' orbit using elliptical paths

• Isaac Newton (1642-1727): Theory of gravity

  • Published Principia in 1687

  • Established the cosmological principle

  • Developed universal gravitational law

The Modern View of the Universe

Galileo's Principle

• Objects fall straight down in any uniformly moving frame of reference

• Mechanical experiments cannot distinguish between uniform motion and standing still

Einstein's Contributions

1. Special Theory of Relativity

• Laws of physics are constant throughout the universe

• Speed of light is constant in all non-accelerated frames of reference

• Introduced concept of space-time

• 14 billion years old universe

2. General Theory of Relativity

• Space-time is affected by the presence of matter

• Explains gravity as curvature of space-time

Effects of Special Relativity

• For objects near light speed:

• Time slows down

• Lengths contract

• Masses increase

Speed of Light

• c = 299,792,458 m/s (exact)

• Approximated as 300,000,000 m/s or 3 × 10^8 m/s

The Big Bang Theory

• Proposed by Georges Lemaître (belgian priest) and Aleksandr Friedmann (russian physicist)

• Universe expanding from an infinitesimally small point

• Supported by Edwin Hubble's discovery of galactic recession (1929)

• Name coined by Fred Hoyle in 1950 (initially as criticism)

• Dark energy contributes to the growth of the universe

Composition of the Universe

• Known matter and energy: ~4%

• Dark energy: ~76%

• Dark matter: ~20%

Dark Energy and Dark Matter

• Dark energy: Accelerating universe expansion

• Dark matter: Interacts only through gravity, opposes dark energy

• Current evidence suggests dark energy is "winning"

• spiral shape for milky way galaxy

Life cycle of a star

• Star: giant ball of hot gas

• Hydrogen and helium act as a fuel for the star via fusion

• Gravity is the force that pulls the star together when it forms

• Floating gas particles begin to combine forming small clouds of gases

• The larger the mass of the nebula the stronger its gravitational field

• Nebula: Forms due to dust and gas particles in space gather due to gravitational forces

• Protostar: Formed when the nebula becomes big enough

• Main sequence star: Forms through nuclear fusion (Pushes back against the gravity pulling the star together and uses hydrogen then helium as fuel)

• Red giant: Formed when the MSS runs out of hydrogen

• White dwarf: Formed through the fusion of heavy elements such as iron

• Black dwarf: Formed after white dwarf cools (no black dwarfs formed atm)

• Red supergiant: Formed when MSS runs out of hydrogen

• Supernova: Formed when RSG explodes

• Neutron star: Formed when supernova explodes; least dense

• Black hole: Formed when supernova explodes; most dense

Classification of stars

• Only Boring Astronomers Find Gratitude Knowing Mass

The Hertzsprung-Russell Diagram

• Illustrates the relationship that exists between the temperature of stars and their luminosity

• Graphs the stars in the universe

• Luminosity (Sun=1) on y-axis

• Temperature (Kelvin) on x-axis

• Key groups:

  • Giants: Massive but cold stars

  • Main sequence: Majority of stars lie and where stars start off

  • White dwarfs: Dim but hot stars

Telescopes

Optical Telescopes

• Used to study objects in visible light

• Two main types:

1. Refracting (Refractor) Telescopes

2. Reflecting Telescopes

Refracting Telescopes

• Uses a lens as its objective to form an image

• Also called dioptric telescopes

• Earliest type of optical telescope

• Invented in the Netherlands around 1608

• Key figures: Hans Lippershey, Zacharias Janssen, Jacob Metius

• Galileo Galilei constructed his own version in 1609

Reflecting Telescopes

• Uses curved mirrors to reflect light and form an image

• Invented in the 17th century as an alternative to refracting telescopes

Advantages:

• Reduces chromatic aberration

• Allows for very large diameter objectives

• Widely used in astronomy research

• Sometimes referred to as "catoptric" telescopes

Radio Telescopes

• Operate in the radio frequency portion of the electromagnetic spectrum

• Typically large parabolic ("dish") antennas

• Used singularly or in arrays

• Located far from population centers to avoid electromagnetic interference (EMI)

• Placed in valleys for additional EMI shielding

STRUCTURE OF AN ATOM

• the smallest part or amount of an element that can exist

Components of an atom

• subatomic particles

• protons

• electrons

• neutrons

• protons and neutrons make up the nucleus

• electrons orbit the nucleus

Protons:

• small

• positive charge

• attracts anything negatively charged

• small mass and charge

• relative mass and charge of 1

• no. of protons tell which element it is

Neutrons:

• relative mass of 1

• no charge

Electrons:

• 1/2000 of a mass of protons

• relative mass of 0.0005

• relative charge of -1

• positive charge of the protons keep electrons from flying away

• total number of electrons=total number of protons

• atomic mass = protons+neutrons

THE UNIVERSE

• 1 movement of heat energy

  explain processes underlying convection and conduction of heat energy and identify situations where waves transfer energy (eg radiation)

  • light and sound are convert-able forms of energy

  • light energy can be converted to other forms with photosynthesis and solar panels

  • sound energy can be transformed into electric energy via microphones

  • thermal energy (aka heat) is transferred from a region of high temperature to a region of cold temperature through either conduction, convection, or radiation.

  • conduction is mainly in solids

  • convection is mainly through liquids and gases

  • radiation can be anywhere, even in a vacuum

  conduction

  • heat travels when fast moving particles vibrate against some more particles which vibrate against more particles, etc.

  • can go through objects or from one to another e.g. cooktop to saucepan

  • heat can travel by conduction at different speeds, depending on the type of material and state of matter

  • gases are poor, liquids are okay, and solids are the fastest

  • metals are generally better conductors than

• 2 waves and energy

  • sound and light travel as waves which transfer or propagate energy

  • two types of waves:

    • transverse waves e.g. water waves. the medium or material carrying the wave oscillates up and down perpendicular to the direction of the energy transfer. they consist of a series of crests and troughs.

    • longitudinal waves aka compression waves e.g. sound waves. the particles move parallel to the propagation of the wave. contains compressions and rarefactions.

  • wavelength = distance between two adjacent crests.

  • amplitude = maximum distance that each particle moves away from its resting/equilibrium position. determines loudness.

  • period = the time it takes from one complete wave to pass a given point (in secs)

  • frequency = number of complete waves that pass a point in one sec. measured in waves/second, or Hertz (Hz). determines pitch. the higher, the closer together—and vice versa.

  • speed = horizontal speed of a point on a wave as it propagates itself, in meters/second

  • also compression waves, e.g. sound waves. outcome three goes into more detail on this.

• 3 sound energy

  • it’s carried as compression waves. sound is essentially just air particles being pushed together then spread apart, bumping into each other and creating a series of compressions and rarefactions.

  • sound can’t travel through empty space, because there are no particles to vibrate, unlike light.

  • Hertz (Hz) are named after Heinrich Hertz, the German physicist who first detected radio waves in 1887.

  • sound waves travel faster in mediums whose particles are closer together - so solid, then water, then air

    • air = 343

    • sea water = 1533

    • rubber = 1600

    • copper = 3560

    • iron = 5130

    • diamond = 12 000

  • dolphins send out high frequency sound (ultrasound) to locate food and communicate.

  • sound moves faster in warm air due to the particles having more kinetic energy, moving quicker.

  • sound with frequencies higher than humans can hear is called ultrasound.

    • e.g. sending a sound wave through a mother’s body, some sound is reflected back from the baby, and can be translated into an image.

    • sonar is another word for ultrasound along the ocean floor.

  • a cathode ray oscilloscope converts sound energy into electrical energy, allowing it to be studied. it uses air pressure changes to detect it, and produces a graph called a waveform.

  • the decibel (dB) scale measures the loudness of sound. it increases by powers of 10 per 10dB; if 0dB is the quietest audible sound, 30 dB is 10^3 (1000) times that, and 40 is 10 000 times that.

  • any sound above 85 dB can cause hearing loss. you know it’s above this if you have to raise your voice to be heard by someone else.

• 4 properties of light

  • describe the occurrence and some applications of absorption, reflection, and refraction in everyday situations

  • light is an electromagnetic wave. it’s transverse.

  • electromagnetic waves can travel through a vacuum and travel through air at 300 000 kilometers per second.

  • the line used to show the path light takes are called rays.

  • individual light rays aren’t visible, but can be seen when the light is scattered through a material, e.g. car headlights on a foggy night, or party lights through smoke.

  • light reflection from curved mirrors - they can be concave (curved inwards) or convex (curved outwards). parallel rays of light are reflected to a focal point; this is outside the mirror for concave, and inside it for convex.

  • transparent = object on the other side visible translucent = light scattered so much object is not clearly visible opaque = can’t see it at all

    

  • light normally goes in straight lines. light can be made to bend by passing it through different transparent media, called refraction—the change in the speed of light when it moves from one substance to another.

  

  • refraction:

  

  • convex versus concave lenses:

  

  • convex are called converging lenses because the light rays are refracted towards each other. concave are called diverging lenses because the rays are refracted away from each other. observed in the diagram

  • dispersion = separation of colours that make up white light; each one is bent out differently when entering or leaving a glass prism.

  • each colour is a slightly different speed, so is refracted at a slightly different angle.

  • the colour of an object depends on which parts of the spectrum are reflected off it towards your eyes. e.g. a red surface absorbs all colours but red.

  • the brain only has three colour sensitive cells—blue, green, and red. colours are just mixes of those. colours that are equal mixes of these colours are called secondary colours, i.e. yellow, magenta, cyan.

• 5 electromagnetic spectrum

  • relate the properties of different types of radiation in the electromagnetic spectrum to their uses in everyday life, including communications technology

  • the frequency of electromagnetic waves is the number of pulses of electric/magnetic fields generated per second.

  

  • gamma waves: radioactive x-rays: medical uses ultraviolet: sunburns you visible spectrum: thank god you’re not blind! infrared: heat maps microwaves: heat your food. satellites. radio waves: transfer information. thank god for mobile data.