The nature of light The light of nature. The Sun is our star The Sun is our star Sunrise Sky and sea...

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The nature of The nature of light light The light of The light of nature nature

Transcript of The nature of light The light of nature. The Sun is our star The Sun is our star Sunrise Sky and sea...

Page 1: The nature of light The light of nature. The Sun is our star The Sun is our star Sunrise Sky and sea Sky and sea Colours of a rainbow Colours of a rainbow.

The nature of lightThe nature of light

The light of natureThe light of nature

Page 2: The nature of light The light of nature. The Sun is our star The Sun is our star Sunrise Sky and sea Sky and sea Colours of a rainbow Colours of a rainbow.

The Sun is our starThe Sun is our star

SunriseSunrise

Sky and seaSky and sea

Colours of a rainbowColours of a rainbow

HalosHalos

LightningLightning

SunsetSunset

Aurora – northern and southern lightAurora – northern and southern light

The MoonThe Moon

StarsStars

Human lightHuman light

Page 3: The nature of light The light of nature. The Sun is our star The Sun is our star Sunrise Sky and sea Sky and sea Colours of a rainbow Colours of a rainbow.

The Sun is our starThe Sun is our starThe Sun is our star – it is classified as a yellow dwarf, because it is The Sun is our star – it is classified as a yellow dwarf, because it is slightly smaller than the average star.slightly smaller than the average star.

The Sun provides the light for most natural phenomena of light, and The Sun provides the light for most natural phenomena of light, and it is of crucial importance for our life on Earth.it is of crucial importance for our life on Earth.

The Sun is a giant sphere of gas – especially hydrogen and helium The Sun is a giant sphere of gas – especially hydrogen and helium – where atoms of hydrogen fuse together to form helium. The Sun – where atoms of hydrogen fuse together to form helium. The Sun transform 600.000.000 tons of hydrogen to helium every second.transform 600.000.000 tons of hydrogen to helium every second.

The nuclear process of the Sun result in both visible and invisible The nuclear process of the Sun result in both visible and invisible radiation – the infrared light and ultraviolet light. The light of our radiation – the infrared light and ultraviolet light. The light of our Sun is almost pure white, but it is in fact composed of many colours Sun is almost pure white, but it is in fact composed of many colours – the spectrum of the Sun.– the spectrum of the Sun.

Page 4: The nature of light The light of nature. The Sun is our star The Sun is our star Sunrise Sky and sea Sky and sea Colours of a rainbow Colours of a rainbow.

The spectrum of colours becomes visible when the light is The spectrum of colours becomes visible when the light is transmitted through a prism. The colours represent different transmitted through a prism. The colours represent different wavelengths – therefore they are refracted at various angles.wavelengths – therefore they are refracted at various angles.

The spectrum of the Sun displays a number of black lines. These The spectrum of the Sun displays a number of black lines. These lines are called Fraunhofer lines or absorption lines, because they lines are called Fraunhofer lines or absorption lines, because they are formed by absorption of light by the matters of the Sun. are formed by absorption of light by the matters of the Sun.

Page 5: The nature of light The light of nature. The Sun is our star The Sun is our star Sunrise Sky and sea Sky and sea Colours of a rainbow Colours of a rainbow.

SunriseSunrise

ssThe sunrise often displays a reddish The sunrise often displays a reddish tint, but the colour is usually less tint, but the colour is usually less distinct than the beautiful red sunset.distinct than the beautiful red sunset.

During sunrise the Sun's light must During sunrise the Sun's light must pass through a much greater thickness pass through a much greater thickness of the atmosphere to reach an of the atmosphere to reach an observer on the ground. This extra observer on the ground. This extra distance causes multiple scatterings of distance causes multiple scatterings of blue light, but relatively little scattering blue light, but relatively little scattering of red light; this is seen as a of red light; this is seen as a pronounced red-hued sky in the pronounced red-hued sky in the direction towards the sun.direction towards the sun.

Page 6: The nature of light The light of nature. The Sun is our star The Sun is our star Sunrise Sky and sea Sky and sea Colours of a rainbow Colours of a rainbow.

Sky and seaSky and seaThe beautiful blue colour of a clear sky The beautiful blue colour of a clear sky is actually an illusion – the atmosphere is actually an illusion – the atmosphere is transparent (if not polluted).is transparent (if not polluted).

The blue colour originate from the white The blue colour originate from the white light of the Sun – although the white light of the Sun – although the white light is composed of all colours.light is composed of all colours.

The blue colour is caused by scattering The blue colour is caused by scattering – Rayleigh scattering – where the – Rayleigh scattering – where the various molecules of air and tiny dust various molecules of air and tiny dust particles scatter the blue and violet light particles scatter the blue and violet light more than any other colour of light.more than any other colour of light.

The blue and violet colours have the The blue and violet colours have the smallest wavelengths of visible light, smallest wavelengths of visible light, which result in major scattering.which result in major scattering.

Page 7: The nature of light The light of nature. The Sun is our star The Sun is our star Sunrise Sky and sea Sky and sea Colours of a rainbow Colours of a rainbow.

The Earth is called the blue planet – The Earth is called the blue planet – mainly because of the oceans, which mainly because of the oceans, which show a distinctive blue colour, when show a distinctive blue colour, when viewed from space.viewed from space.

It is the scattering of light by water It is the scattering of light by water molecules, that gives the blue colour of molecules, that gives the blue colour of the sea. Even relatively shallow waters the sea. Even relatively shallow waters show the blue colouration, because show the blue colouration, because water is more dense than air.water is more dense than air.

The Danish seas are generally greyish The Danish seas are generally greyish green in colour, which is caused by a green in colour, which is caused by a high concentration plankton and the high concentration plankton and the abundance of clouds near the coastline.abundance of clouds near the coastline.

The sea may also reflect the colour of The sea may also reflect the colour of the sky.the sky.

Page 8: The nature of light The light of nature. The Sun is our star The Sun is our star Sunrise Sky and sea Sky and sea Colours of a rainbow Colours of a rainbow.

Colours of a rainbowColours of a rainbowA rainbow is one of natures most loved A rainbow is one of natures most loved phenomena of light. The are many tales phenomena of light. The are many tales of the rainbow – we all know, that there of the rainbow – we all know, that there is a pot full of gold at the end of a is a pot full of gold at the end of a rainbow.rainbow.

The colours arise when the white light The colours arise when the white light of the Sun is refracted and reflected by of the Sun is refracted and reflected by water drops. The white light is a mixture water drops. The white light is a mixture of all colours, each with a characteristic of all colours, each with a characteristic wavelength. The water drops acts as wavelength. The water drops acts as small prisms, which split the white light small prisms, which split the white light into its coloured components.into its coloured components.

This picture shows a distinctive primary This picture shows a distinctive primary rainbow and a faint secondary rainbow.rainbow and a faint secondary rainbow.

Page 9: The nature of light The light of nature. The Sun is our star The Sun is our star Sunrise Sky and sea Sky and sea Colours of a rainbow Colours of a rainbow.

In some cases You may see a double rainbow – one distinct and one with faint colours. This is caused by single and double reflection within the water drops.

Page 10: The nature of light The light of nature. The Sun is our star The Sun is our star Sunrise Sky and sea Sky and sea Colours of a rainbow Colours of a rainbow.

HalosHalosHalos, also known as “icebows”, are also optical phenomena that appear near or around the Sun or Moon.

There are many types of optical halos, but they are mostly caused by ice crystals in cold cirrus clouds located high (5-10 km, or 3-6 miles) in the upper troposphere. The particular shape and orientation of the crystals is responsible for the type of halo observed.

Light is reflected and refracted by the ice crystals and may split up into faint colours because of dispersion, similarly to the rainbow.

Page 11: The nature of light The light of nature. The Sun is our star The Sun is our star Sunrise Sky and sea Sky and sea Colours of a rainbow Colours of a rainbow.

LightningLightningLightning is a violent light phenomena Lightning is a violent light phenomena accompanied by thunder. It has often accompanied by thunder. It has often been attributed to the anger of gods.been attributed to the anger of gods.

Lightning are strong electrical currents, Lightning are strong electrical currents, which originate from turbulent flows of air which originate from turbulent flows of air – especially during humid periods.– especially during humid periods.

The strong turbulence in a cloud result in The strong turbulence in a cloud result in a positive upper part and a negative a positive upper part and a negative lower part. The principle is the same as a lower part. The principle is the same as a balloon rubbed against woolly clothing. balloon rubbed against woolly clothing.

The large potential between cloud and The large potential between cloud and ground – several million volts – may ground – several million volts – may ionise the air and result in lightning. The ionise the air and result in lightning. The lightning heats the air, which explodes in lightning heats the air, which explodes in thunder.thunder.

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The strong turbulence in a thunder-The strong turbulence in a thunder-cloud creates friction between ice cloud creates friction between ice crystals, water droplets and dust crystals, water droplets and dust resulting in static electricity.resulting in static electricity.

If the potential between cloud and If the potential between cloud and ground is sufficiently high ground is sufficiently high –– a a lightning evolves. The lightning lightning evolves. The lightning seeks the easiest way to ground – seeks the easiest way to ground – i.e. a tree.i.e. a tree.

Lightning factsLightning facts

LengthLength ~0,3 – 3 km.~0,3 – 3 km.

But lightning between But lightning between clouds may be over clouds may be over 100 km.100 km.

VoltageVoltage ~ 100.000.000 V~ 100.000.000 Vmax. 1.000.000.000 Vmax. 1.000.000.000 V

CurrentCurrent ~ 30.000 A~ 30.000 A

max. 350.000 Amax. 350.000 A

EffectEffect ~4.000.000.000 kW~4.000.000.000 kW

EnergyEnergy ~250 kWh~250 kWh

TemperatureTemperature ~15.000 °C~15.000 °Cmax. 30.000 °Cmax. 30.000 °C

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A typical cloud-ground A typical cloud-ground lightning flash initiates lightning flash initiates inside the storm.inside the storm.

The electric field cause The electric field cause a negatively charged a negatively charged channel to emerge from channel to emerge from the storm base toward the storm base toward the ground.the ground.

It takes the stepped It takes the stepped leader 50 milliseconds leader 50 milliseconds to reach its full length . to reach its full length .

As the stepped leader As the stepped leader approaches the ground, approaches the ground, its strong, negative its strong, negative charge repels all charge repels all negative charge within negative charge within the immediate strike the immediate strike zone, while attracting zone, while attracting vast amounts of vast amounts of positive charge.positive charge.

The stepped leader The stepped leader actually induces electric actually induces electric channels up from the channels up from the ground known as ground known as "streamers“."streamers“.

The electric potential of The electric potential of the stepped leader is the stepped leader is connected to the connected to the ground and the ground and the negative charge starts negative charge starts flowing flowing DOWNDOWN the the established channel.established channel.

An electric current An electric current wave, called a "return wave, called a "return stroke", shoots UP the stroke", shoots UP the channel as a brilliant channel as a brilliant pulse.pulse.

It takes the current It takes the current about 1 microsecond to about 1 microsecond to reach 30,000 amperes.reach 30,000 amperes.The stroke actually The stroke actually travels FROM the travels FROM the ground INTO the cloud!ground INTO the cloud!

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A thundercloud may produce lightning A thundercloud may produce lightning with intervals of a few seconds – and the with intervals of a few seconds – and the lightning often strike the same spot!lightning often strike the same spot!

Lightning is very dangerous and kill Lightning is very dangerous and kill many people each year.many people each year.

If you hear thunder or see lightning, you If you hear thunder or see lightning, you should go into a house or a car.should go into a house or a car.

If you are unable to do so,If you are unable to do so,you should avoid treesyou should avoid treesand to minimize your risk ofand to minimize your risk ofbeing struck, crouch down on the balls of being struck, crouch down on the balls of your feet – “The lightning crouch”.your feet – “The lightning crouch”.

When inside a house or a car, you When inside a house or a car, you should avoid all apparatus with electric should avoid all apparatus with electric wiring – including the phone.wiring – including the phone.

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Even a plane might be struck by Even a plane might be struck by lightning.lightning.

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SunsetSunsetThe sunset may be a beautiful display The sunset may be a beautiful display of red colours – and the colouration is of red colours – and the colouration is usually more distinct than a sunrise, usually more distinct than a sunrise, due to a higher humidity.due to a higher humidity.

During sunset the Sun's light must During sunset the Sun's light must pass through a much greater thickness pass through a much greater thickness of the atmosphere to reach an of the atmosphere to reach an observer on the ground. This extra observer on the ground. This extra distance causes multiple scatterings of distance causes multiple scatterings of blue light, but relatively little scattering blue light, but relatively little scattering of red light; this is seen as a of red light; this is seen as a pronounced red-hued sky in the pronounced red-hued sky in the direction towards the sun. The direction towards the sun. The scattering is mainly caused by air and scattering is mainly caused by air and water molecules.water molecules.

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Sunset at Mars.Sunset at Mars.

Mars has almost no atmosphere Mars has almost no atmosphere which result in a faint bluish which result in a faint bluish sunset, as the blue colours of light sunset, as the blue colours of light are scattered the most. In the are scattered the most. In the daytime, the sky on Mars is daytime, the sky on Mars is completely transparent.completely transparent.

Dust and volcanic gases also Dust and volcanic gases also scatters the light.scatters the light.

Big volcanic eruptions like Mt. St. Big volcanic eruptions like Mt. St. Helens give rise to especially Helens give rise to especially strong colouration of the sunset. strong colouration of the sunset. The effect last more than one year.The effect last more than one year.

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Aurora – Aurora – northern and southern lightsnorthern and southern lightsNorthern lights are one of the most Northern lights are one of the most beautiful sights in the night.beautiful sights in the night.

Aurora is typical of the circumpolar Aurora is typical of the circumpolar regions of both the north and south regions of both the north and south hemisphere.hemisphere.

Aurora is caused by an interplay of the Aurora is caused by an interplay of the solar wind, the upper atmosphere and solar wind, the upper atmosphere and the magnetic field of Earth.the magnetic field of Earth.

The Aurora is usually seen as greenish The Aurora is usually seen as greenish bands waving over the sky. More rarely bands waving over the sky. More rarely the colours are red or violet. The colour the colours are red or violet. The colour depends on the composition of the depends on the composition of the atmosphere – red in 300-500 km, green atmosphere – red in 300-500 km, green in 100-300 km and violet in 90-100 km.in 100-300 km and violet in 90-100 km.

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The solar wind is composed of The solar wind is composed of hydrogen plasma – protons and hydrogen plasma – protons and electrons – flowing from the Sun. electrons – flowing from the Sun. The activity of the Sun varies and The activity of the Sun varies and may result in a solar storm with a may result in a solar storm with a high number of particles.high number of particles.

The magnetic field transports the The magnetic field transports the charged particles towards the charged particles towards the polar regions of Earth. Within the polar regions of Earth. Within the ionosphere the particles interact ionosphere the particles interact with air molecules – especially with air molecules – especially oxygen and nitrogen. Interaction oxygen and nitrogen. Interaction with oxygen produces red and with oxygen produces red and green colours, whereas nitrogen green colours, whereas nitrogen produce green colours.produce green colours.

Page 20: The nature of light The light of nature. The Sun is our star The Sun is our star Sunrise Sky and sea Sky and sea Colours of a rainbow Colours of a rainbow.

The MoonThe MoonMoonlight is very romantic, but it is Moonlight is very romantic, but it is also give rise to tales of superstition also give rise to tales of superstition and magic phenomena.and magic phenomena.

The Moon is the lightest object in the The Moon is the lightest object in the sky at night. Half the Moon is always lit sky at night. Half the Moon is always lit by the Sun, but the trajectory of the by the Sun, but the trajectory of the Moon results in different views from the Moon results in different views from the Earth.Earth.

Actually the Moon is darker than Earth, Actually the Moon is darker than Earth, but it reflect part of the Sun light, which but it reflect part of the Sun light, which make it appear light in the dark night.make it appear light in the dark night.

Mercury, Venus, Mars, Jupiter and Mercury, Venus, Mars, Jupiter and Saturn may also be visible at night due Saturn may also be visible at night due to reflected light from the Sun.to reflected light from the Sun.

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StarsStarsThe night sky is constantly changing, The night sky is constantly changing, but the apparent movement of the but the apparent movement of the stars is due to the rotation of Earth.stars is due to the rotation of Earth.

Star signs has been known for Star signs has been known for thousand of years – today the brightest thousand of years – today the brightest stars are placed into 88 star signs.stars are placed into 88 star signs.

The stars display a great variety – the The stars display a great variety – the distance to Earth varies, they have distance to Earth varies, they have different ages, size and composition.different ages, size and composition.

Blue stars have a surface temperature Blue stars have a surface temperature up to up to 100.000100.000°C, while our Sun only °C, while our Sun only have a temperature of 5.500°C at the have a temperature of 5.500°C at the surface.surface.

The Magellan Cloud viewed fromThe Magellan Cloud viewed fromthe Hubble telescope.the Hubble telescope.

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Human lightHuman lightOnce upon a time the night belonged to Once upon a time the night belonged to the Moon and stars……the Moon and stars……

Today electric lights of roads and cities Today electric lights of roads and cities become more and more dominant. become more and more dominant. Sometimes we think it is beautiful and Sometimes we think it is beautiful and sometimes we call it light pollution.sometimes we call it light pollution.

Electric light is great, when used with a Electric light is great, when used with a purpose. It is very important that we purpose. It is very important that we use the light where it is needed. To use the light where it is needed. To many lights are poorly designed, many lights are poorly designed, resulting in a waste of energy and light resulting in a waste of energy and light pollution.pollution.

In the cities it may be difficult to view In the cities it may be difficult to view even the brightest star, because our even the brightest star, because our electric light blind us.electric light blind us.

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Even from space we can see the human lights. This picture Even from space we can see the human lights. This picture clearly shows the position of the big cities of Earth.clearly shows the position of the big cities of Earth.