ASTRONOMY

WHAT IS ASTRONOMY?

Astronomy – the study of the universe

Astronomy? Impossible to understand and madness to

investigate.— Sophocles, c. 420 BCE

Rotation: The turning of the Earth on its own axis• Day and Night• 24 hours

Revolution: The orbit of the Earth (or planets) around the sun

• Year• 365.25 days

•Year – the time it takes the earth to orbit once around the sun

•Month – the time it takes the moon to orbit once around the earth

•Day – the time it takes the earth to rotate once around its axis

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Historical figures in the Copernican Revolution

Ptolemy – Greek Astronomer-- 85 – 164 AD--Proposed the Geocentric model of the

universe; that the Earth was the center of the universe/solar system-- Idea accepted for 1400 years-- 1st person to use latitude and longitude

to identify places on Earth

Copernicus – Polish Astronomer-- 1473 – 1543-- Proposed the Heliocentric Model of the universe; that the Sun was the center of

the solar system--He thought the planets orbited the sun

in circles

Historical figures in the Copernican Revolution

Historical figures in the Copernican Revolution

Brahe– Danish inventor, astronomer-- 1546 – 1601-- Invented/Improved instruments for

observing the universe-- Kepler worked for Brahe to observe

the motion of the planets--Modified the Geocentric Model

-- Thought the moon and sun orbited the Earth

-- All other planets orbited the sun

Kepler – German mathematician--1571-1630--Began studying the orbits of planets

with Brahe--Discovered the orbits were not circles,

but were really ellipses (ovals)--stated that the planets move at

different speeds around the sun-- closer planets move faster than

planets further out

Historical figures in the Copernican Revolution

Galileo –Italian Astronomer-- 1564 – 1642--1st to prove Copernicus’ Heliocentric

Model with a telescope--Used the phases of Venus with explained

that Venus in fact revolved around the sun--Spent the last years of his life under

house arrest--discovered the 4 moons of Jupiter-- invented the thermometer-- built compasses for surveying land

Historical figures in the Copernican Revolution

Newton – English scientist, astronomer, mathematician

-- 1642- 1727--1st to describe the concept of gravity--Stated the force that holds us to the

Earth is the same thing that keeps the planets in orbit.

-- Three laws of motion-- Law of Universal Gravitation-- Developed Calculus

Historical figures in the Copernican Revolution

The observed solar system at the time of Newton

SunMercuryVenusEarthMarsJupiterSaturn

(all except Earth are named after Roman gods, because astrology was practiced in ancient Rome)

Three outer planets discovered later…Uranus (1781, Wm Herschel)Neptune (1846 Adams; LeVerrier) Pluto (1930, Tombaugh)

Historical figures in the Copernican Revolution

Hubble – American Astronomer--1889 -1953--in 1929 formulated Hubble's Law,

which determined the age of the universe and that it is expanding

--demonstrated that other galaxies besides our own Milky Way existed

--In the same year Edwin Hubble introduced his Hubble telescope.

-- The Hubble Space Telescope was launched on April 25th, 1990 on the

space shuttle.

Edwin Hubble

Geocentric vs Heliocentric Theories

Earth or Sun Centered?

•Geocentric Theory (Earth-centered) – Ptolemy’s theory that the earth was the center of the universe

•Heliocentric Theory (Sun-centered) – Copernicus’ theory that the sun was the center of the universe

A geographer, mathematician, and astronomer

Developed the theory that the Earth was the center of the solar system

Claudius Ptolemy

…“the natural motion of the Earth ….is towards the center of the universe; that is the reason it is now lying at the center.”

Aristotle, On the Heavens

The Geocentric Theory

• The earth is located at the center of the universe and all the planets revolve around the earth.

Nicolaus Copernicus

To know that we know what we know, and to know that we do not know what we do not know, that is true knowledge.

1473 -1543

A mathematician, and astronomer

Developed the theory that the sun was the center of the solar system

Galileo Galilei1564 - 1642

By using the telescope, Galileo noted that Venus had “phases” like the moon, so it could not orbit Earth, but must orbit the Sun….So, these observations supported Copernicus’ theory!

The Heliocentric Theory

• The Sun is the center of our solar system

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The reasons for seasons – the Earth travels around the sun, and its axis of rotation is tilted by 23.5 degrees to the plane of the orbit. In July, the northern hemisphere is getting more sunlight than in January.

The heliocentric model

Geocentric Model Heliocentric Model

Comparing and Contrasting Historical Theories of the Solar System

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HELL

HEAVEN

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Timeline

Copernicus

1473-1543

Brahe

1546-1601Kepler

1571-1630

Galileo

1564-1642

Newton

1642-1727

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The Copernican Revolution

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Nicolaus CopernicusThe Earth moves, in two ways.• It rotates on an axis (period = 1 day).• It revolves around the sun (period = 1 year).

Tycho Brahe

1546 – 1601Adjusted the Geocentric Theory

Brahe’s precise observations of planet movement lead him to believe that the moon and sun orbited the sun, and the other planets orbited the sun

Through Brahe’s observations with instruments that lead to the invention of the telescope he developed mathematical calculations of the orbits of the planets, sun, and moon,

These calculations helped Kepler determine the equations for planetary motion

Johannes Kepler (1571 – 1630)Developed the laws that describe how the planets move in the solar system

• Planets move in elliptical orbits

Mrs. Scasny’s

Galileo’s discoveries in Astronomy

Galileo did not invent the telescope, but when he heard about the invention he figured out how to build telescopes. He had the best telescopes of his time. He was the first person to use telescopes to look at the heavenly bodies. He was first, so he made the discoveries.

Craters and mountains on the moon 4 Moons of Jupiter Phases of Venus The Milky Way consists of innumerable stars. Sunspots (dark spots) move across the sun’s face.

All of these favored the Copernican (heliocentric) model.

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Galileo’s sketch of the moon as seen from his telescope

A photograph of the moon

Galileo made many specific discoveries in astronomy, through observations by telescope.

The general implications…

● The planets are objects like the Earth – masses – rather than some kind of special heavenly objects. Or, to put it another way, the Earth is just another planet.

● The planets, including Earth, travel around the sun.

● The Universe is a lot bigger than we can see by the naked eye.These ideas could be

dangerous.

The Church decided that the heliocentric model was a heresy.But Galileo continued to argue in favor of the theory, and published his reasoning. The Inquisition in Rome accused him of heresy, and required him to answer.

He was put under arrest and sentenced to prison. But because of his fame and age (70 years old at that time) he was allowed to serve under house arrest in Florence, for the remaining years of his life.

The Trial of Galileo

Isaac Newton1642 - 1727

To explain the motion of the planets, Newton developed three ideas:

1. The laws of motion2. The theory of universal gravitation

1. All objects in the universe attract each other through gravity

2. Heavy objects and those that are close together have the strongest gravitational force

3. Calculus, a new branch of mathematics (oh what fun!!)

Newton solved the premier scientific problem of his time --- to explain the motion of the planets.

Isaac Newton

“If I have been able to see farther than others it is because I stood on the shoulders of giants.”

--- Newton’s letter to Robert Hooke, perhaps referring to Galileo and Kepler

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Newton’s Theory of Universal GravitationNewton and the Apple

(The apple never fell on his head, but sometimes a stupid person will say that, trying to be funny.)

Newton asked good questions the key to his success.

Observing Earth’s gravity acting on an apple, and seeing the moon, Newton asked whether the Earth’s gravity extends as far as the moon.

Warm Up

•How much time passes when…

1. …..the moon goes around the earth 3 times?

2. …..the earth goes around the sun 50 times?

3. …..the Earth rotates 360 degrees?4. …..there are 12 full moons?5. …..the Earth rotates halfway

around?

Warm Up1. What causes the Earth’s seasons?

2. Draw the diagram below and label which season we would be having:

Warm Up1. What causes the Earth’s seasons?

2. Draw the diagram below and label which season we would be having:

SUN