Astronomy Unit

S1-4-03 Investigate how various cultures used knowledge of the position and motion of visible celestial objects.

S1-4-04 Compare and contrast historical perspectives on the relationship between Earth and space.

KEY WORDSConstellation AstrolabePolaris CoordinateRetrograde GeocentricHeliocentric Star

WHAT DO YOU SEE?

1. Agricultural revolution: tracking stars became necessary to accurately mark the growing season.

Position allowed for creation of a calendar that had 365 days in a year.

There was both a spiritual and practical significance to tracking

the sun and stars movements

2. Exploration and Trade: tracking stars used to navigate water for trade and conquest.

Groups of stars are “constellations”

Stars and the Sun became the "landmarks" used.

• used to organize the sky• named for animals and gods

Zodiac is Greek for “circle of animals”

Measuring Angles in the Sky

Astrolabe• Instrument used to calculate the position of

objects in sky with high accuracy

• Perfected during Islamic Golden Age (800-1200s)• Period of enormous growth in math, science and

medicine

Spread of the invention of paper allowed Islamic scholars to collect and translate

the greatest collection of human knowledge in the world – held in a center

called – HOUSE OF WISDOM

Vertical (up/down) angle is called altitude.

altitude azimuth

Horizon – ground - 0°Zenith – directly above - 90°

Horizontal (left/right) angle is called azimuth - measured with a compass

North – azimuth of 0°South – azimuth of 180°

A position in the SKY is given using altitude and azimuth as its “coordinates”

The North Star – Polaris – is used for navigation.• Polaris is due north

LAND coordinates are called longitude and latitude.

Where you observe Polaris in the sky (altitude) equals your latitude on the earth's surface.

What do people in the Southern

hemisphere use?

WHAT CAN WE SEE NOW?

Ptolemy (100 AD)

• Summarized naked-eye 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

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”

Copernicus

HELIOCENTRIC

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 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 life under house arrest

Galileo published his book 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 move around the Sun in ellipses2. Planets move faster closer to the sun, and slower further away3. The further away the planets, the longer it will take to complete its orbit

Comparing Stars and Planets

Star: a very large collection of matter that emits an intense amount of energy (light and heat).

Most planets are brighter than stars Stars twinkle Planets look round in a telescope; stars look like points of light

Only five planets can be seen without a telescope…which ones?

Feature Planet StarLocation in the solar system far beyond the solar

systemDistance from Earth fairly near Very, very, very far

Real size smaller than most stars usually larger than planets

Reason we see it reflects light emits lightSurface temperature usually cold or very

coolvery hot

Composition usually rocks or gases gases under high pressure and temperature

Look does not twinkle twinklesMotion over time very slowly wanders

through constellationsappear to move as part of a constellation

S1-4-01:How do you use an Astrolabe?

S1-4-04:What evidence is there that the sun is the centre of our solar system?

What are the observable differences between stars and planets?

CAN YOU ANSWER THESE QUESTIONS?

KEY WORDSConstellation Astrolabe PolarisCoordinate RetrogradeGeocentricHeliocentric Star