ASTRONOMY PICTURE OF THE DAY How has our Understanding of the Universe Evolved?

Myths, folklore and legends were used to explain what ancient peoples’ observed in the night sky Myths, folklore and legends were used to explain what ancient peoples’ observed in the night sky First Nations believed the night sky was a pattern on a great blanket above (i.e. Ursa Major); this guided their movements. First Nations believed the night sky was a pattern on a great blanket above (i.e. Ursa Major); this guided their movements. See Fig. 1.1 See Fig. 1.1

1. What is a Model? 2. Why do we use models to represent Space?

As long as people have been watching the nightly show of stars and planets, they have sought ways to explain it. As long as people have been watching the nightly show of stars and planets, they have sought ways to explain it. First calendars were lunar, accurate for hunters, gatherers and fishermen. First calendars were lunar, accurate for hunters, gatherers and fishermen. Settled societies needed a more precise solar (Sun) calendar to predict planting and harvesting time Settled societies needed a more precise solar (Sun) calendar to predict planting and harvesting time Figuring out the regular motions of the Sun and Moon with the irregular patterns of the 5 orbiting planets was a puzzle for thousands of years Figuring out the regular motions of the Sun and Moon with the irregular patterns of the 5 orbiting planets was a puzzle for thousands of years How did the Earth fit in??? How did the Earth fit in???

About 2000 years ago, Aristotle proposed a Geocentric, or EARTH CENTRED model to explain planetary motion About 2000 years ago, Aristotle proposed a Geocentric, or EARTH CENTRED model to explain planetary motion

When you go outside at night and look up - what do you see? When you go outside at night and look up - what do you see? To explain why the distant stars didn’t move, Aristotle hypothesized that they were attached to the outermost sphere – like stars glued to a ceiling! To explain why the distant stars didn’t move, Aristotle hypothesized that they were attached to the outermost sphere – like stars glued to a ceiling! His ideas were aided by the math and geometry of Pythagoras and Euclid. His ideas were aided by the math and geometry of Pythagoras and Euclid.

Although this model explained the phases of the moon, it could not explain some observations like why do Mars, Jupiter and Saturn loop backwards across the sky Although this model explained the phases of the moon, it could not explain some observations like why do Mars, Jupiter and Saturn loop backwards across the sky Geocentric Model Geocentric Model Geocentric Model Geocentric Model

1530 Copernicus made observations that led him to conclude that the Sun was at the center and the planets revolved around it (Copernican Model)!! 1530 Copernicus made observations that led him to conclude that the Sun was at the center and the planets revolved around it (Copernican Model)!!

1610 Galileo Galilei gave further proof when looking through a telescope Galileo Galilei gave further proof when looking through a telescope. Wandering planets (retrograde motion) made sense if they revolved around the sun. Wandering planets (retrograde motion) made sense if they revolved around the sun. Wandering planets retrograde motion Wandering planets retrograde motion He also observed lunar mountains, moons orbiting Jupiter, sunspots and phases of Venus with his telescope He also observed lunar mountains, moons orbiting Jupiter, sunspots and phases of Venus with his telescope Which was not much stronger than binoculars used today Which was not much stronger than binoculars used today

In 1614, Galileo was accused of heresy for his support of the Copernican theory that the sun was at the centre of the solar system. This was revolutionary at a time when most people believed the Earth was in this central position. In 1616, he was forbidden by the church from teaching or advocating these theories. In 1614, Galileo was accused of heresy for his support of the Copernican theory that the sun was at the centre of the solar system. This was revolutionary at a time when most people believed the Earth was in this central position. In 1616, he was forbidden by the church from teaching or advocating these theories. In 1632, he was again condemned for heresy after his second was published. This set out the arguments for and against the Copernican theory in the form of a discussion between two men. Galileo was summoned to appear before the Inquisition in Rome. He was convicted and sentenced to life imprisonment, later reduced to permanent house arrest at his villa south of Florence. He was also forced to publicly withdraw his support for Copernican theory. In 1632, he was again condemned for heresy after his second was published. This set out the arguments for and against the Copernican theory in the form of a discussion between two men. Galileo was summoned to appear before the Inquisition in Rome. He was convicted and sentenced to life imprisonment, later reduced to permanent house arrest at his villa south of Florence. He was also forced to publicly withdraw his support for Copernican theory.

Galileo’s discoveries added credibility to the Heliocentric model, but it could not predict planetary motion accurately Galileo’s discoveries added credibility to the Heliocentric model, but it could not predict planetary motion accurately Johannes Kepler came up with the solution. Johannes Kepler came up with the solution. By using detailed observations of the planets from Tycho Brahe, Kepler discovered the planets moved in ELLIPSES not circles. (Circles are too perfect to be likely) By using detailed observations of the planets from Tycho Brahe, Kepler discovered the planets moved in ELLIPSES not circles. (Circles are too perfect to be likely) Modern Model of the Solar System

Technology has been used for thousands of years to measure time: Technology has been used for thousands of years to measure time: – Merkhet (Egyptians) to predict star motion – Quadrant (Egyptians) to measure star altitude – Astrolab (Arabian) to chart star positions – Cross-staff (Gurson) 1300’s to measure the angle between the moon and stars – First optical telescope 1500’s

As lens grinding technology improved (think from my parents records to your iPods) the telescopes became more powerful. As lens grinding technology improved (think from my parents records to your iPods) the telescopes became more powerful. As our viewing ability got better, the vast distance between objects in space became obvious. As our viewing ability got better, the vast distance between objects in space became obvious. – The Earth is only a small planet orbiting an average star – The Sun is only one arm of the Milky Way. – The Milky Way is only 1 of 20 local galaxies we have looked into!

Kilometers is too SMALL of a unit to measure the vast distances in space! Kilometers is too SMALL of a unit to measure the vast distances in space! Astronomical unit (AU) used for local solar system distances. Astronomical unit (AU) used for local solar system distances. – 1AU is the AVERAGE distance between the center of the SUN and the EARTH Light-year used for interstellar and intergalactic distances. Light-year used for interstellar and intergalactic distances. – 1 light year is the distance light travels in a YEAR! – Because the speed of light is 300,000 km/s in a vacuum, a light years is about 9.5 trillion kilometers – 9,500,000,000,000 kilometers!! Now that’s FAR OUT!!