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 are 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 DistancesSolar DistancesDistances on Earth are measured in a Distances on Earth are measured in a

variety of units, depending on the variety of units, depending on the distancedistance

If really small:If really small: MicrometersMicrometersSize of a school:Size of a school: MetersMetersFrom WPG to VAN:From WPG to VAN: KilometresKilometres

Units must change, because it would Units must change, because it would not make sense to measure the not make sense to measure the distance from Winnipeg to Vancouver distance from Winnipeg to Vancouver in millimetres!in millimetres!

If this distance was 1900 km, how If this distance was 1900 km, how many mm?many mm?

Almost 2 billion!Almost 2 billion!1900 km = 1, 900, 000, 000 mm1900 km = 1, 900, 000, 000 mm

Solar System Solar System MeasurementsMeasurements

The distance from the Sun to the The distance from the Sun to the Earth is 155 million kmEarth is 155 million km

This is too large of a number to use, This is too large of a number to use, therefore when measuring distances therefore when measuring distances in the Solar System we use in the Solar System we use Astronomical UnitsAstronomical Units

Each AU = 155 million kmEach AU = 155 million km

Outside the Solar SystemOutside the Solar SystemFor any measurements outside the For any measurements outside the

Solar System, the AU is not very Solar System, the AU is not very usefuluseful

Closest star (Proxima Centauri) is Closest star (Proxima Centauri) is 270 000 AU away270 000 AU away

Therefore we need to use a new unitTherefore we need to use a new unit

Light YearLight YearA light Year is the distance light can A light Year is the distance light can

travel in one yeartravel in one yearLight moves at 3 X 10Light moves at 3 X 108 8 m/sm/sEarth is 155 million km awayEarth is 155 million km awayHow long does it take light to reach How long does it take light to reach

the Earth?the Earth?

1) Change km to m1) Change km to m

1.55 X 101.55 X 1088 km = 1.55 X 10 km = 1.55 X 101111 m m

2) Divide this distance by the speed 2) Divide this distance by the speed of lightof light

1.55 X 101.55 X 1011 11 m / 3 X 10m / 3 X 108 8 m/s = 516.75 s m/s = 516.75 s

The Third Rock From The SunThe 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 SpaceEarth 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 SeasonsReasons 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 DatesImportant 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