earth & universe

The Earth and the Universe 1

The Earth and the Universe

Ever since the first humans looked in wonder at the stars in the night sky, we have longed

to know more about the Universe. The first use of astronomy was to measure time. The

early Egyptians used the appearance of the brightest star, Sirius, to mark the start of the

season when the Nile River was in flood. The Greek astronomer Ptolemy made accurate

measurements of the movement of the planets in about 180AD. Before the invention of

the telescope, people could only use their eyesight for looking at heavenly objects and

measuring positions of the stars.

But for around 400 years, most of our knowledge about the night sky came from

telescopes, mainly the refracting telescope that uses only lenses and the reflecting

telescope that uses mirrors and lenses. Galileo Galilei (1564-1642) made his first

observations using a telescope in the early 17th century.

Sir William Herschell (1732-1822) started observing the night sky in 1771, using a small

reflecting telescope. He discovered the planet Uranus, the first planet to be discovered

with the help of a telescope, since we are not able to see this planet with the naked eye.

From the 1930s, radio telescopes were able to detect other rays and waves from space as

we shall see later on.


The Universe Today, we have the technology to explore deeper into the Universe than ever imagined.

Our Earth is only just one very tiny part of the vast universe - a small rocky planet travelling around a medium sized star, the Sun, in one of billions of galaxies. A Galaxy is a huge group of millions of stars in space. But galaxies are often millions of times further

apart than the stars within the galaxy. Normal galaxies come in three different shapes;

spiral, elliptical and irregular. The universe is made up of more than 10 000 million such

galaxies. Nobody knows really where the universe begins or ends. We have so far

explored only a very small part of the universe.

The universe is everything that exists, mostly made up of empty space. It stretches further

almost than the human mind can imagine - we already know that the universe reaches at

over 13 billion light years in every direction so we see the stars as they were 13 billion

years ago! So the universe is even older than this. It is filled with matter in many different

shapes, sizes and forms. It contains dust and gases; planets such as the Earth and billions

of stars such as our Sun, our Milky Way Galaxy and countless of other galaxies.

We can see about 5000 individual stars in the night sky. On a really clear night, it is also

possible to see one or two galaxies. The most visible part of our own Milky Way Galaxy

is the part of the sky that looks like a misty cloud. It is really a band of millions of stars.

The Milky Way Galaxy looks like a thin disc with a dense, bulging centre. It is about

2000 light years thick and about 100 000 light years across. Gravity keeps the stars to-

gether in a galaxy and like most things in the universe, the galaxies all rotate. It contains

an estimated 100 000 million stars and they orbit its centre at a speed of 274 km/s.


There are other galaxies, the most famous being the Andromeda Galaxy, which is close to

the constellation Pegasus. It is the most distant object visible to the naked eye and looks

like a small fuzzy patch. The Andromeda galaxy is a huge spiral galaxy, 2.2 billion light

years away and is thought to contain at least 300 billion stars.

The light year

The universe is so huge that we cannot measure it in kilometres, or even millions of

kilometres. Imagine writing down in kilometres the distance of the Andromeda galaxy

from earth! So astronomers measure the size of the universe or the distance of stars by

using the speed at which light from these objects travel. In empty space, light travels at a speed of 3 x 108m/s. Using this speed for a year will give you a distance of 9.5 x 1012km

So the distance that light travels in one year is 9.46 million, million kilometres. This is

called a light year and it is a measurement of distance not time! In fact light from the Sun,

which is about 150 million kilometres from Earth, takes 8 minutes to reach us. The

nearest star, Proxima Centauri, is 4.225 light years from Earth.

The Solar System The sun is a very ordinary star among thousands of millions of other stars in the Milky

Way Galaxy. Its outer layer or coronas temperatures reach as high as 2 million oC. It has

a planetary system, called the Solar System, which is made up of nine planets and other left over material that did not form into planets surrounding it. The planets start off with

Mercury, which is at an average distance of 58 Mkm from the Sun. then comes Venus, Earth, Mars (these planets are known as the four rocky inner planets), Jupiter, Saturn, Uranus, Neptune and Pluto. Between the orbits of Mars and Jupiter lies an area of one


Kind of left over material, the asteroids. These are lumps of rock, some of which are many kilometres long.

The planets vary enormously in size. They also vary in their distance from the Sun.

Planets dont give their own light (they are not stars), they reflect the Suns light. Because

they are much nearer than stars, they appear to move slowly against the background of

the stars. The planets are held in their orbits by the gravitational pull of the sun. The orbit

of each planet is not quite a circle. It is a slightly squashed circle called an ellipse. All planets in our solar system orbit in the same plane, except Pluto. They are not all travel-

ling at the same speed, the planets nearer to the Su travel more quickly so they have a

shorter year.

1 Mercury Mercury is closest to the Sun and small for a planet (about the size of our Moon). It has

no atmosphere and is covered in craters. The side of planet facing the Sun is very hot,

about 430 oC.

2 Venus Venus is almost as big as the Earth, but very unpleasant. It is covered in clouds of

sulphuric acid, with an atmosphere of carbon dioxide at a very high pressure. Because of

the CO2 and the Greenhouse Effect it is even hotter than Mercury.

3 Earth From space, Earth is a blue planet with swirls of cloud. It is the only planet with water

and oxygen and living things. It is at the right distance from the Sun, with the right

chemicals, to support life. Other stars may have planets with the same conditions.

4 Mars Mars - the red planet - is a cold desert of red rocks, with huge mountains and canyons.

There is no life on Mars. It has a thin atmosphere of carbon dioxide, and two small

moons. Between Mars and Jupiter there are thousands or rocks, called asteroids.

5 Jupiter Jupiter is the cold giant of the planets. It has no solid surface, being mainly liquid

hydrogen and helium, surrounded by gases and clouds. The Great Red Spot is a giant

storm three times the size of Earth. Some of the 16 moons have volcanoes.


6 Saturn Saturn is another gas giant, very like Jupiter. The beautiful rings are not solid. They are

made of billions of tiny chunks of ice, held in orbit by the pull of Saturns gravity. As

well as the rings, Saturn has more than 20 moons.

7 Uranus Uranus is another giant planet. It looks pale green, with very faint rings and 15 moons. It

was discovered by William Herschel in 1781. It is unusual because its axis is tilted right

over, so that it is lying on its side as it goes round the Sun.

8 Neptune Neptune is the twin of Uranus. They are both about 4 times the size of Earth. Neptune is

bluish, due to the thick atmosphere of cold methane. It has 8 moons, one with volcanoes.

The Great Dark Spot is a storm about the size of Earth.

9 Pluto Pluto is the smallest of all, discovered in 1930. We dont know much about it. Plutos

orbit is not circular as the others. Most of the time its orbit is outside Neptunes but

between 1979 and 1999 its orbit was inside Neptunes. Some astronomers think there is a

planet 10 beyond Pluto.

The

planets

Avr. Dist. From Sun

Mkm Earth=1

Diameter

(Earth = 1)

Density

(kg/m3)

Avr. Temp oC

Mass

Earth=1

Gravity

(N/kg)

orbit time

(years)

No. of

moons

1-Mercury 58 0.4 0.4 5500 +430 to 0.1 4 0.2 0

2-Venus 108 0.7 0.95 5200 +470 0.8 9 0.6 0

3-Earth 150 1 1 5500 +15 1 10 1 1

4-Mars 228 1.5 0.5 4000 -30 0.1 4 1.9 2

Asteroids

5-Jupiter 778 5 11 1300 -150 320 26 12 16

6-Saturn 1427 9.5 9 700 -180 95 11 30 20 + rings

7-Uranus 2870 19 4 1300 -210 15 11 84 15 + rings

8-Neptune 4497 30 4 1700 -220 17 12 165 8

9-Pluto 5900 39 0.2 500 -230 0.002 4 248 1


Moons Moons are heavenly bodies which orbit planets. It is the force of gravity which holds the

moons in orbit. The Earth has only one moon but other planets have quite a few. We can

only see the moon because it reflects sunlight. The phases of the moon happen, depending

on how much of the illuminated side of the moon we can see.

Beyond Pluto is another kind of left over material, the comets such as Halleys Comet. These are bodies of rock, ice and dust. They are very highly elliptical orbits, which bring

them close to the Sun and then far out in the solar system beyond Pluto. When they fall

near the Sun they speed up as the pull of gravity increases. The dust and gas are blown

away from the Sun and shine in the sunlight, to form a long tail. When some comets pass

close to the Sun they heat up and give off material, forming a tail. Comets also give off

small rocky particles which form many of the meteors or shooting stars that we see.


The Earth Look up at the sky on a clear night. The sky seems to arch overhead like a vast

star-studded dome. Ancient people believed that the stars were actually stuck on the

inside of a sphere, surrounding the Earth. Each day, the Sun and stars seem to move

across the sky, rising in the East and setting in the West. Ancient civilisations attribute

this motion to the rotation of the celestial sphere around the Earth. The apparent rotation of the celestial sphere means that the sky changes in appearance

continually during the night. The night sky also looks different, from season to season,

according to the latitude of your position. To many people today, the continually varying appearance of the sky is as confusing as it was to ancient man.

Of course, the Sun and stars do not really move of their own accord around the heavens

each day; it is actually the daily rotation of the Earth on its axis that makes them appear

to move so.

The Earth takes 24 hours to rotate once on its axis (one complete revolution), then for each hour of time the stars will appear to move 15o across the sky. The Earths daily

rotation, obtained from the observations of stars, is the basis of our time keeping.

But the Earth does not only spin on its axis. It is also moving on its orbit around the Sun

and it is pulled into orbit by a centripetal force. This is the gravitational force between the mass of the Sun and the mass of the Earth. The time taken for the Earth to orbit the Sun once is known as a year, it lasts approximately 365 days and 6 hours. Because the Earth does not orbit the Sun in an exact number of days, we have to add an extra day to

the calendar every four years to keep the calendar with the seasons. Each year con-

taining an extra day is called a leap year.

An additional confusion, is that the Earths axis of rotation is not perpendicular to the

plane of its orbit, but instead tilts at an angle of 23.5o from the vertical. This tilt of the Earths axis causes the seasons.


In June, the earths North pole is tilted 23.5o towards the Sun

and so there is summer in the northern hemisphere. Six

months later, in December, the South pole is presented to the

sun, causing summer in the southern hemisphere. In summer,

the days last longer than the nights, while the opposite is true

in winter. But on two days each year, night and day are equal

in length. These are the occasions on which the sun crosses

the celestial equator, and are known as the equinoxes. The vernal equinox occurs on 21st March and the autumnal occurs on the 23rd September.

There is one more effect we need to take into account to complete our understanding of

the appearance of the sky, and that is the effect of changes in latitude. An observer at one

of the Earths poles would see only half the sky. Above would lie the celestial pole, the

celestial equator would be just on the horizon. Each night, the stars would spin around the

pole, with none appearing to rise or set. An observer standing at the Earths equator, by

contrast, would see the celestial poles lying on the north and south horizon respectively,

and the celestial equator would be above. Each night, stars would appear to rise in the

East, move overhead and set in the west as the Earth turned. During one year, an observer

would see the entire sky that can be observed form that latitude.

Observations stationed at latitudes on Earth midway between the poles and the equator

see an intermediate amount of the sky. Some stars appear to circle the pole each night

without setting (circumpolar stars) while others rise and set. Inhabitants of the Earths

northern hemisphere can easily check their latitude, because a fairly bright star, Polaris,

lies close to the north celestial pole. Unfortunately there is no equivalent star near the

south celestial pole.


Gravitational Forces About 1666, at the early age of 24, Isaac Newton investigated the motion of a planet

moving in its orbit round the Sun. Newton concluded that a universal law could be stated

for the attraction between any two particles of matter, not just planets! In fact, all objects attract each other and gravity is the force of attraction which acts between all masses. He found that the force of attraction between two given particles of a certain mass is

inversely proportional to the square of their distance apart. From this law it follows that

the force of attraction F, between two particles of masses m and M respectively, at a distance d apart, is given by the following equation.

F = G m M M m m d2 Force : 1 1/4

Distance: 1 2

G is a universal constant known as the gravitational constant. This expression for F is Newtons law of gravity. This law is applied to the motion of planets round the Sun, to satellites round the Earth and to the moon.

From this law we can conclude that:

1. The greater the mass, the greater the force of attraction.

2. The greater the distance, the smaller the force of attraction. In fact if the distance

doubles, the gravitational pull is 1/4. This is the inverse square law. The graph illustrates how the force of gravity varies as you get closer to a planet.

We have already seen that the Suns

force of gravity holds the planets in

orbit, but planets are not equally

attracted by the Sun. Mercury is

very near to the Sun. To counteract

this strong force of gravity, the

planet must move faster and cover

its orbit quicker. So mercury moves

at a faster speed than Pluto since it is

nearer to the Sun.


Satellites Imagine firing a cannon from the top of a high

mountain. The canon ball would fall back to the

Earth just like when you shoot a ball. But if the

cannon ball is fired faster, it falls farther away. If

the cannon ball is fired at 8 km/s (25 times the

speed of sound), then it would still fall towards

the Earth, but because of the curving of the

Earth, the ball would stay the same height above

the ground. It is then a satellite in orbit and the

force of gravity keeps pulling it into orbit.

So an object becomes a satellite when it is propelled fast enough - at a speed of 28 800

km/s - to be able to fly in a continuous fall or arc around the Earth without being pulled

back by gravity. Satellites fly above the Earths atmosphere at a height of at least 160 km.

The higher the orbit, the slower the speed of the satellite and the longer it takes for one complete orbit. A close-look observation satellite will fly in a low orbit around the Earth so that its cameras can take high-resolution images. However, a communications

satellite is situated in a high orbit so that it can provide services to as large an area of the

world as possible.

The speed of a satellite can be calculated very easily. If

the radius of the orbit is R, then the circumference of the circle is 2 R. If the time for one orbit (the periodic time) is T, then:

Speed = Distance travelled = 2 R time taken T Example: A satellite at a height of 700 km above the Earths surface, orbits with a

period of 100 minutes. What is its speed if the radius of the Earth is 6400 km?


A Geostationary Satellites used for Communications A satellite moves very fast, but it can seem to be standing still! If the satellite is put at

just the right height and speed, it will take 24 hours to go round the Earth. This is the

same time as the Earth takes to spin once, so the satellite appears to stay over one place.

Most communication satellites are in geostationary orbit above the Equator (equatorial orbit) at a height of 36 900 km so that they appear stationary when viewed from Earth.

Communications satellite technology has developed at a rapid rate. Just 30 years ago the

rather basic Telstar satellite was transmitting TV signals to a ground station for onward

transmission by land-line to peoples homes. Today, satellites can beam TV pictures di-

rectly into millions of homes - and from not just one channel but hundreds of different

ones at the same time. Some important scientific advances have made this possible. Also

the satellites, with their perfectly fashioned antennas, have extremely high transmitting

power - they are supplied with large amounts of electricity by advanced solar panels.

Lastly, the high power transmissions mean that satellite-receiving dishes can be smaller.

Satellite provide numerous communications services other than TV. Some are able to han-

dle 30 000 simultaneous phone, data and fax calls.

Modern communications technology

allows us to keep in touch with each other

from almost anywhere in the world. The

network of satellites in space provides

instant communications whether by

telephone, mobile phone, fax, pager,

computer or e-mail. If you telephone to

America, a microwave radio signal is transmitted from a dish aerial up to the satellite.

The satellite then transmits it down to another aerial dish in America. Microwaves are used because they travel in a narrow beam, in a straight line and pass through the Earths

atmosphere. The satellites are positioned in such a way that a mobile phone user is within

the range of at least one satellite at any time. Today a typical communications satellite

weighs 3500 kg providing high power transmission in many wavebands. Using 6000W of

power from solar cells, it transmits to thousands of receiving dishes as small as 1m in

diameter or smaller.


B Low Polar Orbit Satellites Satellites can be launched into polar orbits which are usually lower. As the Earth turns on

its axis, the satellite passes over a different part of the Earth on each orbit. The time taken

for each full orbit is just a few hours and so it allows the whole surface of the Earth to be

monitored each day. This finds many applications:

1 Weather Satellites A fleet of polar weather satellites from USA, Russia, Europe, India and Japan provide a

daily World Weather Watch service to the worlds population. The satellites help

meteorologists to make instant weather forecasts including early warnings of weather

extremes such as hurricanes. These early warnings enable thousands of people to

evacuate areas about to be hit. The familiar weather satellite pictures we see on our TV

screens are only one part of the weather story. Satellites also take images in different

wavelengths, highlighting other aspects of the weather, such as temperature and

atmospheric content.

2 Earth Observation Satellites Daily maps from Earth observation satellites show the surface temperature anywhere on

the Earth, both on land and at sea. Other images reveal the water content in the atmos-

phere and its pattern of circulation, and monitor the damage to the earths ozone layer

caused by the emission of greenhouse gases. So international meteorological satellites in

polar and geostationary orbit above the earth are continually monitoring the worlds

weather as well as changes to our environment. Meteosats successor, called Metop, is a

typical example of todays environmental satellite.

3 Navigational Satellites Navigation satellites can provide accurate information to within a few metres of a per-

sons location anywhere in the world - on land, at sea or in air. They can also work out the

speed of a moving person or object at within 0.1m/s. This technology is vital for all types

of military operations, from guiding a missile to its target or telling on undercoat agent exactly where he or she is. Russia and the USA operate fleets of navigational satellites.

The US Air Force operates a navigational service called the Global Positioning System, GPS. It consists of 24 Navstar satellites, which are at all times equally spaced apart in six different paths around the Earth.


Many satellites have been launched for purely scientific purposes - to learn as much as possible about the Earth and its place in space. The discovery of radiation belts around

the Earth by Americas first satellite, Explorer 1, is a classic example of this. Other

satellites have been launched to study the radiation belts, the Earths magnetic field and

its upper atmosphere.

Many research and development satellites have been launched to test out new equipment

to be used on future operational spacecraft, while other satellites have conducted experi-

ments using the lack of gravity in space. Space processing could lead to a revolution in

the worlds pharmaceuticals and electronics industries.

4 Astronomical Satellites New astronomical satellites have now been developed that observe the Universe not as

we would see it with our eyes but using different wavelengths, such as x-rays and UV

light. Some of these telescopes have been launched into space to obtain a better view of

the Universe, without the interference of the Earths atmosphere. An example of such a

satellite is the Hubble Space Telescope (HST), which was launched into space in April 1990. This telescope is probably the greatest advance in astronomy. It can see 50 times

deeper into space than the most powerful telescope on Earth. Using a telescope on Earth

to see into space is rather like being under water in a swimming pool and trying to see

outside the pool. It is very difficult to see through the thick atmosphere. In space the HST

is not influenced by any atmosphere. With the help of the HST, astronomers are now able

to see sites they used to dream of - black holes, quasars and even possible planets moving

around other stars. Many of the visible light images are combined with other observations

made in other wavelengths by the HST, producing more complete photos.

Life of stars Stars are incandescent balls of gas, giving out their own heat and light, similar to our own Sun. While the stars stay fixed in position, the planets orbit a central star, mov-ing slowly across the sky. The planets appear bright to us because they reflect light from

the Sun - they do not emit their own light. But how are stars born? What keeps them

glowing? And how do they grow old and die? Astronomers believe they now have

answers to most of these questions.


Stars are, thought to be, formed from giant clouds of dust and gas in space, known as nebulae. One famous site of star formation is the great nebula in Orion, visible to the naked eye as a hazy patch, and particularly impressive viewed through a telescope. Stars

are forming today inside the Orion Nebula. Radiation from the largest and hottest of these

stars makes the whole nebula glow.

Stars start to form when part of a gas cloud like the nebula breaks up into individual blobs

as a result of random swirling motions in the cloud. These blobs collapse under the

inwards pull of their own gravity. As they shrink, becoming smaller and denser, pressures

and temperatures build up inside them until nuclear reactions switch on at their cores.

When this happens, a gas blob becomes a true star.

Our star had a similar birth, then the planets began to form. The heat of the Sun pushed

some of the lighter gas and ice into a doughnut-shaped cloud, leaving the heavier dust in

the gap. Because of gravity the dust began to stick together, eventually making the four

rocky inner planets. In the same way, the outer planets formed from ice, then collected the

gas to become gas giants like Jupiter.

Stars, it seems, do not come into being on their own, but in vast groups. The Pleiades

cluster in the constellation of Taurus is an example of a star group that has formed from a

giant gas cloud. Our Sun was probably a member of a similar cluster when it was born

4700 million of years ago, but the stars of that cluster have long since drifted apart. Some

nebulae contain no illuminating stars, and therefore are dark. These can only be seen in

silhouette against a brighter nebula or the Milky Way star field.


Stars do not burn in the usual sense of the word, to give us light. They are powered by nuclear reactions at their centres, which turn hydrogen to helium, releasing huge amounts of energy in the process. This is similar to the reaction, which occurs in a hydrogen bomb, but in stars the reaction occurs in a more controlled way.

Stars are made largely of hydrogen, which is the simplest and most abundant element in

the Universe. For instance 70% of the sun (by weight) is hydrogen, and most of the

remainder is Helium, the second simplest and most abundant element. All other elements

make up less than 2% of the Suns mass. These figures are typical of other stars.

In the nuclear furnace at the centre of the sun, atoms of hydrogen are crushed together to

make atoms of Helium, a process called fusion. The temperature at the core of the Sun where this reaction takes place is estimated to be 15 million oC. Each second 600 million

tons of hydrogen in the sun are turned into helium, with 4 million tons going to produce

energy. Even at this rate, the sun has enough hydrogen stocks to last for about another

5000 million years. The sun is believed to be in stable middle age, roughly half way

through its life cycle.

Eventually a star starts to run out of hydrogen at its core, having turned it

all into helium. Burning hydrogen then moves out into the surrounding

zone. When this happens, the star gets hotter inside and the result of this

extra energy release is that the star swells up in size. As it swells, its

surface temperature drops so that it becomes red in colour. The star has

become a red giant. So the stars colour and brightness depend on its temperature. Blue stars are the hotter, while red stars are the coolest. It

follows that most red stars are very old and have expanded to a huge size

compared to their original size.

A red giant can be as much as 100 times the size of the present Sun.

When our Sun reaches this stage, in billions of years, it will engulf the

Earth, thereby ending life on our planet. For the next stage in the stars

development, the helium core also becomes sufficiently heated to ignite

and partake in nuclear reactions, this time forming carbon. The extra

energy released expands the star still further - so much so that its outer

layers drift off into space, forming a stellar smoke ring or planetary nebula. Planetary nebulae have nothing to do with planets, they get their name from the fact that through a telescope they resemble the disc of a planet.

At the centre of the expanding shell of gas lies the exposed core of the former red giant

star. This small, hot core is known as a white dwarf. A white dwarf star may contain as much mass as the Sun, compressed into a ball the size of the Earth. White dwarfs are


Made of such dense materials that a handful of material would weigh several tons. Since

white dwarfs are so small, they are very faint and difficult to spot through telescopes.

They cool off slowly like a dying fire to become a black dwarf, eventually fading into invisibility. This is predicted to be the final fate of the Sun.

All stars of less than about four times the mass of the Sun go through this life cycle,

although at different rates, depending on their masses. A star like Sirius, for example,

with about twice the mass of the Sun, can live for no longer than 1000 million years,

which is 1/10 the suns predicted life time. At the other hand of the scale, red dwarf stars -

far smaller and cooler than the sun - are predicted to live at least 10 times as long as the

sun, because they use up their nuclear fuel more slowly. Red dwarfs, being long-lived, are

probably the most abundant stars in the Galaxy, although they are so faint they are

difficult to spot.

Stars with more than about 4 solar masses die a spectacular death. A

large star burns hotter (blue giant) and runs out of fuel sooner. They

expand and cool to red super-giants, larger and brighter even than red

giants, and then a series of run-away nuclear reactions sets in at their

core. The result is that the star erupts in a gigantic nuclear explosion

known as a supernova. In a supernova explosion, the star may flare up in brightness by thousands of times, so that for a few days or

weeks it is giving out as much light as an entire galaxy!

As the star erupts, complex nuclear reactions occur which give rise to

all the known chemical elements. These atoms are scattered into

space by the explosion to mix with gas clouds and then to gather up

to make new stars. One famous supernova was seen by Middle

Eastern and Oriental astronomers in 1054AD. Some stars blow up

themselves completely to bits in a supernova.

But in many cases the heavy core of the dead star remains as an

object even smaller than a white dwarf which then becomes a

neutron star (or pulsar). If this still has a big mass it continues to collapse under its own gravity. The pull of gravity becomes so strong that nothing can escape it, even light. It be-

comes a black hole.

Cloud of gas gathered gas becomes more compact nuclear fusion process where

by gravity as a result it get hotter hydrogen is changed into

helium - a star is born!


small stars expand to outer layers expand to

red giants become planetary nebulae.

Core collapses to become a

white dwarf

Medium stars expand to supernova explosion

Hydrogen runs out yellow/orange super giants leaving a neutron star

large stars expand to supernova explosion

become white super giants leaving black hole

Beginnings and endings Edwin Hubble, the astronomer who established the existence of galaxies outside our own,

announced in 1929 that the galaxies seemed to be moving apart from each other at speeds

that increased with distance, as though the entire Universe was expanding like a balloon

being inflated.

This amazing and fundamental discovery, was made by analysing the spectrum of light

from distant galaxies. Their light turned out to have increased in wavelength, a common

effect caused by rapid motion of a light source away from the observer, and named the

Doppler effect after the German physicist Christian Doppler who described this principle in 1842. The effect is known as a red shift, because red light lies at the long - wavelength end of the spectrum and so an increase in wavelength means that light is shifted towards

the red end. In other words, the frequencies are all slightly lower than they should be. Its the same effect as a car horn, sounding lower-pitched when a car is travelling away

from you. The sound drops in frequency.


Hubble found that the amount of red shift in a galaxys light depends on its distance from

us, with the farthest galaxies having the greatest red shifts and hence they must be mov-

ing away from us the quickest. The relationship between red shift and distance is called

Hubbles Law and it means that by measuring the red shift in light from a galaxy we can

estimate its distance. Hubbles discovery might seem to imply that our local group of

galaxies is the centre of the Universe from which all else is receding, but this is not the

case. An observer on any galaxy would see exactly the same effect as we do. The entire

universe is expanding and hence all the galaxies are moving apart from each other. There

is no known central point in the universe.

Scientists have three main theories about the creation of the Universe:

1 the steady state theory The steady state theory says that the Universe has always been existing, expanding and

that new material is constantly being created and there is the same amount of matter in

the same place. This theory is no longer supported since astronomers can see that the uni-

verse looked different in the past. A further blow to the steady state theory is that radio as-

tronomers have heard what they believe is the echo of the Big Bang - an explosion

which marked the origin of the Universe. In 1965, the American physicists Arno Penzias

and Robert Wilson detected a faint radio noise coming from all over the sky. In 1978, this

earned them a Noble Prize. The reason for this noise is that space in not entirely cold, but

has a temperature of 2 or 3 degrees above absolute zero. The slight warmth pervading the

Universe is interpreted as being the energy left over from the Big Bang.

2 The pulsating Universe theory According to the pulsating Universe theory, all matter is flying apart from a heavily com-

pacted mass and will eventually slow down, begin to contract and become so condensed

that it will explode again.

3 the Big Bang theory The Big Bang theory suggests that the universe began in an explosion about 15 billion

years ago and will continue to expand forever. According to this theory, the early universe

was very hot and dense, with all its matter and space packed into a very small area, then it

exploded. As it cooled down, the Universe expanded and astronomers believe it is still

expanding. These estimates are not very accurate because it is hard to tell how much the

expansion has slowed down since the Big Bang. The rate at which the expansion is


Slowing down is an important factor in deciding the future of the Universe. Without the

force of gravity, the universe would expand forever. However the attraction between all

masses in the universe tends to slow the expansion down.

The eventual fate of the universe depends on how fast the galaxies are moving apart and

how much total mass there is in it. We can measure the speed with which the galaxies are

separating but we just dont know how much mass there is in the universe as most of the

mass appears to be invisible (in black holes and interstellar dust). There are two ways the

universe could go:

1. If theres enough mass compared to how fast the galaxies are currently moving, the

universe will eventually stop expanding and begin contracting. This would end in a

Big Crunch, which would be followed by another Big Bang and the endless cycles of explosions and contractions.

2. If theres too little mass in the Universe to slow the expansion down, then it could

expand forever with the universe becoming more and more spread out.

Who knows what and when will be the end?!

earth & universe

Documents

vast universe

billions of stars

individual stars

night sky

billions of galaxies

milky way galaxy

normal galaxies

small reflecting telescope