Celestial Motion: Looking Up

Constellation Polaris Star Planet OUTCOME QUESTION(S): S1-4-03: Why were the position and motion of visible celestial objects important to past cultures? How can you measure the location of objects in the sky? Vocabulary & Concepts  Constellation Polaris Star Planet

The Science of Astronomy Astronomy is the study of the Universe Scientists who study Astronomy are known as Astronomers Like most scientists, Astronomers aim to answer specific questions What kind of questions do you think Astronomers are trying to answer?

The Science of Astronomy Astronomers differ from most other scientists in one aspect… Unlike most scientists, Astronomers cannot actually touch the objects they study because everything is so far away. This makes Astronomy an observational science rather than an experimental science

Early History of Astronomy Ancient people saw seven celestial bodies moving through the stars: Sun Moon Mercury Venus Mars Jupiter Saturn

Early History of Astronomy 5 of these objects were considered to be “special stars” due to their movement patterns. Ancient people called these special stars planets. Only five planets can be seen without the naked eye…Which ones? My Very Educated Master Just Showed Us Nine Planets

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 celestial movements

Zodiac is Greek for “circle of animals” 2. Exploration and Trade: tracking stars used to navigate water for trade and conquest. Stars and the Sun became the "landmarks" used. Groups of stars are “constellations” used to organize the sky named for animals and gods Zodiac is Greek for “circle of animals”

STONEHENGE

A star (Sun) and all the objects orbiting it What is Up there? Stars: very large collection of matter that emits an intense amount of energy (light and heat). Planets: collection of matter that is generally spherical and revolves (orbits) around a star. Our solar system: A star (Sun) and all the objects orbiting it

Scientists estimate our solar system is 4.6 billions years old Feature Planet Star Location Distance from Earth Real size Reason we see it Surface temperature Composition Look Motion over time Far beyond the solar system In the solar system Fairly near Very, very, very far Smaller than most stars Larger than planets Reflects light Emits light Cold or very cool Very hot Rocks and/or gases Gases A constant light Twinkles / flickers Very slowly wanders through constellations Move only as part of a constellation Scientists estimate our solar system is 4.6 billions years old

CAN YOU ANSWER THESE QUESTIONS? Why were the position and motion of visible celestial objects important to past cultures? How can you measure the location of objects in the sky? Vocabulary & Concepts  Constellation Polaris Star Planet

Ptolemy Copernicus Galileo 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 & Concepts  Ptolemy Copernicus Galileo Kepler Retrograde Geocentric Heliocentric Solstice Equinox

Celestial Motion: History and Earth

Planet is Greek for “wanderer” 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 Planet is Greek for “wanderer” Observation: Some planets seem to move backwards in orbits: “Retrograde motion”

Called the “Founder of modern astronomy” 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”

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/moon 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 evidence confirming Copernicus’ mathematics, and was accused of heresy by the Church. Would not recant his work as a mistake and spent entire 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 He received loads of money from the Church in hopes he could prove the Earth-centred view…he failed Brahe built one of the best observatories in the world 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 (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?

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.”

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 Fall Equinox (Sept 22) 12h and 12h Summer Solstice (June 21) Longest Day 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

What do people in the Southern hemisphere use? The North Star – Polaris – is used for navigation. Polaris is due north How high Polaris is in the sky (altitude) equals your latitude on the earth's surface. What do people in the Southern hemisphere use? LAND coordinates are called latitude and longitude.

This is Winnipeg

Measuring Angles in the Sky   Measuring Angles in the Sky

Astrolabe Instrument used to calculate the position of objects in the sky with high accuracy Perfected during Islamic Golden Age (800-1200s) Period of enormous growth in math, science and medicine

(measured with a compass) Vertical (up/down) angle is called altitude: 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” altitude azimuth

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 & Concepts  Ptolemy Copernicus Galileo Kepler Retrograde Geocentric Heliocentric Solstice Equinox