Celestial Motion: History and Earth

Ptolemy Copernicus Galileo OUTCOME QUESTION(S): S1-4-04: What evidence is there that the sun is the centre of our solar system? S1-4-05: How does the position and motion of Earth produce day/night, the phases of the moon, and the seasons? Vocabulary & People  Ptolemy Copernicus Galileo Kepler Retrograde Geocentric Heliocentric Solstice Equinox

Planet is Greek for “wanderer” Ptolemy (100 AD) Summarized naked-eye observations and knowledge of that time Earth was centre of the universe - Geocentric In good with the Church Planet is Greek for “wanderer” Observation: Some planets seem to move backwards in orbits: “Retrograde motion”

Ptolemy’s proposed mini-loops were called “epicycles” GEOCENTRIC Ptolemy Ptolemy’s proposed mini-loops were called “epicycles”

Called the “Founder of modern astronomy” Copernicus (1473) Produced mathematical evidence for a Sun- centered system – heliocentric Easily explained retrograde motion Proved Earth rotated on its axis once daily and revolved around the sun once yearly Not in good with Church Called the “Founder of modern astronomy”

HELIOCENTRIC Copernicus

What can we see now?

The first one was a simple refracting telescope First optical telescope made in Netherlands (1608): Uses curved optical elements Gathers and collects light to a focal point Increase apparent size and apparent brightness The first one was a simple refracting telescope

Different energies provide astronomers with different information a Refracting telescope - lenses focus an image b Reflecting telescope - mirrors focus an image Telescopes are classified by the energy detected: Optical – visible light Infrared – heat energy Ultraviolet, X-ray Different energies provide astronomers with different information

Galileo (1564) Perfected the telescope (built a few years earlier) First to state and use the scientific method Discovered moons around Jupiter 1 Proof that not all objects traveled around Earth Venus had phases (day/night) like Earth 2 Proof that it traveled around the Sun Not in good with the Church

Galileo’s drawings and scientific records of his observations

Galileo published his book confirming Copernicus’ mathematics, and was accused of heresy by the Church. Would not recant his work as a mistake and spent life under house arrest By the way, Pope John Paul II made a public apology and exonerated Galileo in 1992

Brahe’s goal was to prove Copernicus incorrect Kepler (1571) Worked as assistant for astronomer, Tycho Brahe Brahe’s goal was to prove Copernicus incorrect Brahe built one of the best observatories in the world He received loads of money from the Church in hopes he could prove the Earth-centred view…he failed Measured positions of 777 stars and five planets that were known at that time

Kepler used Brahe’s data after his death to describe three laws of planetary motion: 1. Planets orbit the Sun in ellipses 2. Planets move faster close to Sun, and slower farther away 3. Planets farther away have a longer orbit

Earth rotates towards the East The Earth rotates on its axis once a day. At any time - half of Earth is in “day” and half in “night.” Earth rotates towards the East winter summer The Earth revolves around the Sun once a year. At any time - half of Earth is in “winter” and half in “summer.”

Time-lapse photography to show the stars spinning as we rotate on our axis

Our axis is tilted at 23.5o (degrees) This tilt and the curvature of the Earth is responsible for the variations in the Sun’s energy – and creates our seasons.

Summer Solstice (June 21) Summer: not only more “direct” but also more hours of the Sun’s energy Spring Equinox (Mar 21) 12h and 12h Winter “indirect” energy Winter Solstice (Dec 21) Shortest Day Summer Solstice (June 21) Longest Day Fall Equinox (Sept 22) 12h and 12h Summer “direct” energy

What do you notice?

That’s why there is a “dark side” of the Moon Moon Rotation Moon completes 1 rotation on its axis in the same time as it completes 1 revolution around the Earth (synchronous) We always see the same side facing the Earth That’s why there is a “dark side” of the Moon Orbit is elliptical Tilted 5° Mean Distance: 384,400 km

Phases of the Moon Shines only by reflected sunlight Depends on fraction of sunlit half visible to us

CAN YOU ANSWER THESE QUESTIONS? S1-4-04: What evidence is there that the sun is the centre of our solar system? S1-4-05: How does the position and motion of Earth produce day/night, the phases of the moon, and the seasons? Vocabulary & People  Ptolemy Copernicus Galileo Kepler Retrograde Geocentric Heliocentric Solstice Equinox