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”
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