Early Astronomy The Geocentric Model Geo Earth Centric

Early Astronomy

The Geocentric Model Geo = Earth Centric = Centred

Geocentric Model • First described by Aristotle around 300 B. C. • All celestial bodies seem to move across sky from East-West • Earth must be at the centre, with everything moving around us • Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn – all fixed on circular spheres orbiting the Earth.

• About 400 years later, new discoveries in mathematics showed problems with the Geocentric model • Ptolemy (around 100 A. D. ), updated the model, adding “epicycles” to the orbits of the planets • This helped to explain the retrograde motion of some planets • In total this model lasted for about 2000 years!

The Heliocentric Model • Helio = Sun Centric = Centred

• Copernicus (1500) devises a new model, with the Sun at the centre • Many new discoveries were being made at this time to help prove this model • Kepler (1600) improved the model by using ellipses for the orbits instead of circles

Formation of the Universe • Because it is believed that the Universe is expanding, it must have started off as something small • The Big Bang occurred around 15 -20 billion years ago • Formation of stars and galaxies shortly after

We are all Made of Stars • An average star (like our Sun) lives for about 10 billion years • Therefore, many stars have died out since the Big Bang • When a star explodes and dies, it is called a super nova These explosions supply the energy to make the elements which everything is made up from

The Solar System • The Sun, and anything orbiting the Sun including the planets & their satellites, comets, meteors, and asteroids. • First existed as a solar nebula (a huge cloud of gas and dust) • Gravity pulls the nebula inward, and it begins to rotate • As the nebula rotates, it forms a flat disk

A Rotating Solar Nebula

• The material in the disk is what formed the planets • This is why all the planets are on the same plane, and all orbit in a CCW direction • The material in the centre is what formed the Sun

Galaxy • A large group of stars, gas, and dust bound together by gravitational attractions • The Milky Way is our galaxy • There approx 200 billion stars in the Milky Way • Scientist estimate that there are 100’s of billions of galaxies

The Universe • All space, along with all the matter and radiation in space • Anything and everything!

Solar Distances l Distances on Earth are measured in a variety of units, depending on the distance l If really small: l Size of a school: l From WPG to VAN: Micrometers Meters Kilometres

l Units must change, because it would not make sense to measure the distance from Winnipeg to Vancouver in millimetres! l If this distance was 1900 km, how many mm? l Almost 2 billion! l 1900 km = 1, 900, 000 mm

Solar System Measurements l The distance from the Sun to the Earth is 155 million km l This is too large of a number to use, therefore when measuring distances in the Solar System we use Astronomical Units l Each AU = 155 million km

Outside the Solar System l For any measurements outside the Solar System, the AU is not very useful l Closest star (Proxima Centauri) is 270 000 AU away l Therefore we need to use a new unit

Light Year l. A light Year is the distance light can travel in one year l Light moves at 3 X 108 m/s l Earth is 155 million km away l How long does it take light to reach the Earth?

l 1) Change km to m 1. 55 X 108 km = 1. 55 X 1011 m l 2) Divide this distance by the speed of light 1. 55 X 1011 m / 3 X 108 m/s = 516. 75 s

The Third Rock From The Sun A geologically active planet - earthquakes, volcanoes - erosion from wind & water Large amounts of liquid water - 70% of Earth’s surface Unique atmosphere among the planets - 80% nitrogen, 19% oxygen

• When the Earth first formed (4. 6 billion years ago) it was entirely molten • Heavier elements sank towards the centre • Lighter elements rose towards the surface • Solid inner core (iron), molten outer core, mantle, crust

Earth in Space • The Earth revolves around the Sun once every 365 days • The Earth rotates on it’s axis once every 24 hours • The axis is tilted 23. 5 degrees • Always pointed in the same direction (North Star)

Reasons for the Seasons • For half the year the Northern Hemisphere is tilted toward the Sun (Summer!) • For half the year the Northern Hemisphere is tilted away from the Sun (Winter) • This is the cause of the seasons!

Important Dates • • June 21: Summer Solstice Arctic circle 24 hours daylight March 21, Sept. 21: Spring & Fall Equinox Everywhere receives 12 hours of day & night • Dec 21: Winter Solstice • Arctic circle 24 hours of darkness

The Moon • The most visible object in the night sky • Can see surface features with the naked eye (Light grey/dark grey areas) • Dark grey areas called “Maria” • Latin for sea (People used to think these areas were large bodies of water)

Characteristics • • • The Moon has many craters Most small, but some up to 100 km No water on the moon No atmosphere Surface covered with a fine powder and rock fragments

How did the Moon Form? • Early Earth struck by Mars sized object • Tons of debris flown into space, orbits around the Earth • This debris later condensed together to form the Moon • Proof for this is in the composition of the Moon

Moon Movements • The Moon revolves around the Earth every 27 days • The Moon revolves at the same rate it rotates on its axis (1 moon day = 27 days!) • Because of this, we never see the far side of the Moon • New moon to full moon: Waxing • Full moon to new moon: Waning

The Sun • The only star in our SS • Makes up 99. 9% of all the mass in the SS • The source of almost all the energy on Earth. • Where does this energy come from?

Thermonuclear Reactions • The Sun is made up of mostly Hydrogen and Helium atoms • It is so hot at the core that 2 hydrogen atoms can fuse together to form helium • This is called nuclear fusion • Power plants use nuclear fision (opposite)

Sun Atmosphere • The photosphere is the visible layer of the Sun • Not really a “surface” • The chromosphere is visible only during an eclipse • The corona is the outermost region of the Sun’s atmosphere

Sun Spots • Regions of the photosphere that appear dark because they are cooler than the surrounding areas • Can be about the size of the Earth • Galileo first discovered sunspots • He found they moved across the sun • This proved the sun rotated on its axis

• • Sunspot cycle every 11 years Last sunspot maximum: 2001 Last sunspot minimum: 1996 When there are many sunspots, Earth is usually warmer • When there are fewer sunspots, Earth is usually colder

Solar Flares • Huge eruptions from the photosphere • Occur in large sunspot groups • Radiation from these flares hit Earth, interfere with radio communication, create intense northern lights

Asteroids • Left over pieces of rock and metal that did not form planets • Large asteroid belt between Mars and Jupiter…………Destroyed planet? ? ? • Some up to 1000 km in diameter • Paths crossing other asteroids, moons, and planets

Comets • AKA “dirty snowballs” • Humans have been aware of comets for a very long time, often considered bad omens • Discovered that comets reappear in cycles • Halley’s Comet: Every 76 years. • Last appearance in 1986, next in 2061

• Comets are made of two parts • 1) Head (coma): Small dense nucleus, surrounded by a large gas section • 2) Tail: Made of fine particles of dust and gas. Can be very long • The tail can only be seen when the comet approaches close enough to the Sun for it to melt the iced gas • The tail always points away from the Sun • With each pass, the comet loses some of its mass

Others…… • Meteoroid: Lumps of rock and metal, pulled into Earth’s ATM • Once a meteoroid enters the ATM it burns up due to friction • Meteor: A meteoroid that completely burns up (shooting star) • Meteor showers common several times a year • Meteorite: An unburnt portion, Strikes the Earth

Meteor Showers • On any given night you can expect to see a few “shooting stars” each hour • At certain times though, you can see many more • Jan 4 110/h • Aug 12 68/h • Oct. 21 30/h • Nov. 17 10/h • Dec. 14 58/h

Stars • If you ever looked up at the night sky, you can see that the stars are not all the same • They vary in Brightness • They vary in colour • They vary in size

Star Brightness • Depends on the distance and size of the star • The Sun is so bright because it is so close to us, but it is only an average star • Luminosity: A measure of the total amount of energy a star radiates per second • Some stars are 30, 000 times more luminous than the Sun

Star Colour • Stars come in a variety of colours • Scientists can tell the surface temperature by the colour of the star • Red stars are cooler (Surface T 3000 C) • Blue stars are hotter (Surface T 20000 C) • The Sun is a yellow star (6000 C)

Star Size • Stars come in a variety of sizes • Small stars are called dwarfs • Large stars are called giants • Our star is an average star

Dwarf Stars • Low mass stars • Slowly convert hydrogen into helium (over 100 billion years) • May stay a dwarf all its life, our start as an average star, and turn into a dwarf • Red, white and Black dwarf stars depending on age

Average Stars • Consume their hydrogen in about 10 billion years • (Our sun is about 5 billion years old) • Once H is burned up, energy production stops • Core collapses due to gravity • Increased T = increased pressure

• The outer layers of the star begin to expand • May become 100 times its original size • Now called a red giant • When our Sun reaches this stage it will engulf Mercury, Venus, Earth and Mars! • Eventually the outer gases are burnt off, and all that is left is a super dense core

Massive Stars • • • Consume their hydrogen more rapidly Millions of years, not billions These stars become super giants Life span shorter, but more energetic Two fates once core collapses and explodes (super nova) • The star may turn into a neutron star, or a black hole

Space Technology • Telescope: a device used to magnify distant objects • Come in all sizes and shapes • Refractor telescope uses glass lenses • Reflector telescope uses mirror lenses • The wider the telescope, the more light it can process

Observatories • A building designed and equipped with a powerful telescope to observe the night sky • Best places: Arid regions, mountain tops • Above cloud cover, away from light pollution • Hawaii & Chile are two of the best places in the world, multiple observatories

Hubble Telescope • What better place for a telescope than outerspace? • Launched in 1990 • Orbiting 600 km above the Earth • Built by the European Space Agency (ESA) and NASA • Starting to become outdated

The Future • The next generation telescope coming in 2009 • Called the James Web Space Telescope

Mir Space Station • Launched in 1986 by the Russians • Since then has had multiple upgrades • Serves as a permanent site for astronomers to conduct their research • Shared by multiple countries