Celestial Motion:History and Earth

OUTCOME QUESTION(S):S1-4-04:How was the process of science important in showing 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 HeliocentricSolstice Equinox

Ptolemy (100 AD) • Hypothesized “epicycles” to explain observations

and knowledge of that time• Earth was centre of the universe - Geocentric• In good with the Church

Observation:Some planets seem to move backwards in orbits:“Retrograde motion”

Planet is Greek for “wanderer”

Ptolemy

GEOCENTRIC

Ptolemy’s proposed mini-loop “epicycles” solved the retrograde

motion puzzle

Copernicus (1473)• Produced mathematical evidence for a Sun- centered system – heliocentric

• Much simpler explanation for retrograde motion• Hypothesized Earth rotated on axis once daily and

revolved around Sun once yearly • Not in good with Church

Called the “Founder of modern astronomy”

Copernicus

HELIOCENTRIC

WHAT CAN WE SEE NOW?

First optical telescope made in Netherlands (1608):

The first one was a simple refracting telescope

• Uses curved optical elements• Gathers and collects light to a focal point• Increase apparent size and apparent brightness

Telescopes are classified by the energy detected:• Optical – visible light• Infrared – heat energy• Ultraviolet, X-ray

Different energies provide astronomers

with different information

a Refracting telescope - lenses focus an image b Reflecting telescope - mirrors focus an image

Galileo (1564)• Perfected the telescope (built a few years earlier)• First to state and use the scientific method

• Discovered moons around Jupiter1 Proof that not all objects traveled around Earth

• Venus had phases (day/night) like Earth/moon 2 Proof that it traveled around the Sun

• Not in good with the Church

Galileo’s drawings and scientific records of his

observations

• Would not recant his work as a mistake and spent entire life under house arrest

Galileo published his evidence confirming Copernicus’ mathematics,

and was accused of heresy by the Church.

By the way, Pope John Paul II made a public apology and exonerated Galileo in 1992

Kepler (1571)

• Brahe built one of the best observatories in the world

• Worked as assistant for astronomer, Tycho BraheBrahe’s goal was to prove Copernicus incorrect

• Measured positions of 777 stars and five planets that were known at that time

He received loads of money from the Church in hopes he could prove the

Earth-centred view…he failed

Kepler used Brahe’s data after his death to describe three laws of planetary motion:

1. Planets orbit the Sun in ellipses (not circles)

2. Planets move faster close to Sun, slower farther away

3. Planets farther away have a longer orbital period

What do we know today?

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

The Earth revolves around the Sun once a year. At any time - half of Earth is in “winter” and half in “summer.”

summer

winter

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“direct” energy

Winter“indirect” energy

Summer: not only more “direct” but also more hours of the Sun’s energy

Summer Solstice (June 21)

Longest Day

Winter Solstice (Dec 21)

Shortest Day

Fall Equinox (Sept 22)

12h and 12h

Spring Equinox (Mar 21)

12h and 12h

WHAT DO YOU NOTICE?

• 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

• Orbit is elliptical• Tilted 5°• Mean Distance:

384,400 km

Moon Rotation

That’s why there is a “dark side” of the Moon

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:How was the process of science important in showing 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 HeliocentricSolstice Equinox