Signals from Space

We live on a planet called Earth, this is a big lump of rock that orbits the sun. There are 7 other planets orbiting the sun. They make up the solar system along with the moons , asteroids and dwarf planets.

Signals from SpaceThe sun is a star, it is our source of heat and light energy.

Our sun is one of millions of stars that make up the Milky Way galaxy ( a group of stars ).

The milky way galaxy is one of

millions of galaxies that make

up the universe. Exoplanets orbit stars

In other solar systems.

Electromagnetic Spectrum

This is a group of radiations ( waves ) that travel at 3 x 108 ms-1 through air / vacuum. They are grouped according to their frequency / wavelength , have different properties and are detected by different detectors.

The different signals convey different types of information e.g. search for ET life uses radio waves but black holes can be detected by searching for gamma rays.

Electromagnetic Spectrum

Remember that

Radiation Detector

TV and Radio Aerial

Microwaves Aerial

Infrared Photodiode/ (hand)

Visible Light Eye

Ultra Violet Fluorescence of chemicals

X Rays Photographic film

Gamma rays Geiger Muller tube

xfv Increasing frequency

Electromagnetic Spectrum

Calculate the frequency of 300 m radio waves. Remember that all members of the electromagnetic radiation travel at 3 x 108ms-1.

V = 3x108 ms-1 λ = 300 m f = ?

xfv

Hzxxv

f 68

101300

103

Light Year

This is the distance that light would travel in one year:

Distance = speed x time

( this is equivalent to going around the earth 250 million times )

mxxxxxxtxvd 158 1046.9606024365100.3

Light YearObject Time for

light to travel from earth

Distance

( m )

moon 1.2 seconds

sun 8 minutes

Next nearest star

4.7 years

Edge of Milky Way Galaxy

100 000 years

Telescopes

Used to gather signals from distant objects ( signals can be any member of electromagnetic spectrum ):

Spectroscopy

White light can be split into its spectrum by a prism. The shorter the wavelength of light the more refraction and bending of the light.

Blue λ = 450 nm

Green λ = 550 nm

Red λ = 650 nm

Red

Green

Blue

Continuous spectrum• All colours merge into each other , like a rainbow. • Hot objects emit a continuous spectrum• Temperature of star can be calculated by looking

at spectrum• Cool objects emit red light but as the temp

increases , red, green and blue light are emitted :it glows white

Line Spectrum

• Emitted by low pressure gases• Chemical composition of stars can be evaluated• Each element has its unique spectrum• These are called emission spectrum

The Big BangBig Bang theory states approximately 13.7 billion years ago the universe came into existence . It started as a single point and a rapid expansion occurred. Initially the temperature was very hot and only ‘energy existed’. As it expanded , it cooled and ‘matter’ was formed . Initially particles called quarks and electrons were formed then eventually protons and neutrons. The simplest elements then followed : Hydrogen then helium.

Big Bang : The EvidenceOther galaxies are moving away from us , this suggests that at one time all the ‘matter’ in the universe must have been at a single point. This time was approximately 13.7 billion years ago.Cosmic Microwave background radiation is detected coming from all directions : This is the remnants of the ‘Big Bang’. ( Initially the temperature was very hot but it has cooled over time , we have seen that different temperature objects have different spectra. )

Advantages of Space ExplorationApart from allowing us to better understand ‘where we come from’ Space Exploration has had a huge impact on society :Use of satellites to predict weather/ storms/GPSUse of sensors to monitor volcanoes/ investigate the bodyUse of new materials in insulation/ replacement body parts/ scratch resistant lensesImprovements in computing…………

Projectile MotionThis has two components : a constant horizontal velocity and a

vertical velocity that accelerates uniformly at 9.8 m s-2.

Horizontal velocity remains constant if we ignore frictional forces and spin.

Vertical velocity changes uniformly as gravitational force acts on object.

This results in a curved

trajectory :

Projectile motionExample

Calculate the horizontal distance ,s , traveled

( range )and the height , h , of the cliff if the car takes 5 s to hit the ground.

20 ms-1

Height of cliff, h,

Range,s,

Now that’s what I call a speed bump.

0

10

20

30

40

50

60

0 1 2 3 4 5 6

velo

city

( m

s-1)

time(s)

velocity time graph

Area under graph = ½ b x h = ½ x 5 x 49 = 122.5 m

Calculate the resultant velocity of the car as it hits the sea :Draw a vector diagram:

20 ms-1

Ɵ49 ms-1

Use Pythagoras to work out hypotenuse 52.9 ms-1

Use trig to work out angle , Ɵ67.80

Resultant velocity is 52.9 ms-1 , 67.80 below the horizontal.

Newton’s Thought Expt

The ball is fired horizontally but gravitational force accelerates it towards the earth. It crashes at point A

If the horizontal velocity is increased it can ‘reach ‘ a little further around the earth to B.

If the horizontal velocity is increased further it can travel right round the earth.

Newton’s Thought Expt 3

If the horizontal velocity of the ball is increased further it flies off into space.The ball orbits the earth because gravitational force is pulling it towards the centre. The ball wants to travel in a straight line but gravitational force pulls it inwards.This is why satellites , natural and man made, orbit planets.

Re entryWhen the space shuttle re enters the earth’s atmosphere there are huge frictional forces acting against it.Some of the shuttle’s kinetic energy is turned into heat energy.To stop the craft becoming too hot inside, the underside is painted black, this is a good emitter of infra red radiation. The underside is also covered with tiles that have a low specific heat capacity and a low thermal conductivity. This ensures that the temperature of the tiles rises quickly( but accordingly lots of heat is radiated to the surroundings ) and a small amount of heat energy is transferred into the cabin.

Example energy change

The space shuttle, 100 tonnes, slows down from 7 500 ms-1 to 750 m s-1 when it hits the earth’s atmosphere. Assume that all this change in kinetic energy is turned into heat energy Calculate the maximum temperature rise if the specific heat capacity of the thermal tiles, 2000kg, is 50 J kg-10C-1.

ExampleUse Ek = 0.5mv2 to calculate kinetic energy change.

Ek before = 2.8125 x 1012

Ek after = 2.8125 x 1010

Ek change = 2.78 x1012 J

Use Eh = Ek = cm T

Cxx

x

mxc

ET h 07

12

1078.2200050

1078.2

Obviously a lot of the heat energy is re radiated otherwise the shuttle would melt.

Ablative Heat Shields

When a material turns from a solid to a liquid or from a liquid to a gas energy is required. When water evaporates off your skin you cool down. This idea is used to cool down some space craft on re entry.

Part of the heat shield is designed to burn away, the gases produced carry some heat energy away , cooling the spacecraft.

SatellitesThere are two main groups of satellites : geostationary and polar orbiting.Polar orbiting satellites orbit over the poles hence they will ‘see’ all parts of the earth over a period of time. They orbit as low as 1000 km with a period of 100 mins . The 24 GPSSatellites orbit at a height of 19,200 km with a period of 12 hrs.Satellites can be used to gather info for weather forecasting, ‘spying’, Monitoring sea levels, temperatures…

Geostationary satellites

They orbit, 36,000 km above the equator with a period of 24 hrs. They appear above the same point on earth and so are used chiefly for communications. 3 satellites can be used to send signals around the entire earth.

Parabolic Reflectors

Signals are gathered over a large area and reflected to a focus. This increases the strength of the signal. The microphone is situated at the focus.

Parabolic Reflectors

If a transmitter is situated at the focus the energy is transmitted as a parallel beam. This allows SKY to direct signals to specific parts of europe. Car headlamps use similar Physics.