electromagnetic radiation consists of photons that carry energy photons can
behave simultaneously as a particle or a wave a phenomenon called wave particle
duality because of a photons wave behavior electromagnetic radiation has
frequency and wavelength frequency is the number of waves passing a point in
one second wavelength is the distance between one peak and the next
Think about two different types of electromagnetic radiation say gamma rays
and radio waves if we measure their wavelengths we'll find that gamma rays
have a much shorter wavelength and a correspondingly higher frequency because
the distance between two peaks is shorter so that more waves pass a point
in 1 second frequency and wavelength are inversely related
we can also calculate a waves energy using Planck's equation according to
this equation energy equals Planck's constant times frequency so an
electromagnetic radiation that has higher frequency has higher energy and
shorter wavelength whereas an electromagnetic radiation that has lower
frequency has lower energy and longer wavelength different kinds of
electromagnetic radiation have different frequencies wavelengths and energies if
we put these properties in order we end up with the electromagnetic spectrum the
electromagnetic spectrum consists of radio waves microwaves infrared visible
light ultraviolet x-rays and gamma rays radio waves have the lowest frequency
the lowest energy and the longest wavelength whereas gamma rays have the
highest frequency the highest energy and the shortest wavelength visible light is
located between infrared and ultraviolet light and occupies only a very small
part of the whole spectrum
between 1666 and 1672 Isaac Newton carried out various experiments on color
he managed to separate the various colors from red to violet from white
light using a prism the separation of visible light into its different colors
is known as dispersion after light passes through a prism surface each
color follows a different path because each color has a different wavelength
and this difference results in a different angle of daeviation on passing
through the prism different colors are bent through different angles and the
colors are separated from each other if we put a second prism in the path of the
separated colors we can combine them and make white light again the dispersal of
light explains how rainbows form water droplets in the air behave as tiny
prisms and separate the colors of sunlight each color corresponds to a
particular electromagnetic radiation because each color has an energy-level
frequency and wavelength if we take a closer look at the color spectrum red
has the lowest energy whereas violet has the highest energy
electromagnetic radiation has properties other than energy wavelength and
frequency for example electromagnetic radiation doesn't need a medium in which
to travel and so can travel through a vacuum also it has the highest possible
speed the speed of light is about 300,000 kilometers per second which
means that with the help of some reflectors it could whiz seven and a
half times around the earth in one second
even though electromagnetic radiation travels so fast
it still takes sunlight about eight minutes to reach Earth this gives some
impression of how far the Sun is away from us and the Sun is very close
compared to most things in space the next nearest star system is Alpha
Centauri which is really made up of two brightest stars and a much dimmer one
about 4.4 light-years away this means that even if we had advanced technology
to travel very close to the speed of light it would still take is about four
and a half years to get to Alpha Centauri and if Alpha Centauri were to
explode this instant something it can't actually do it would take four point
four years before we could know anything about it the closest large galaxy to the
Milky Way is the Andromeda galaxy we can observe it with our eyes alone as a
fuzzy patch in the night sky yet it lies 2.2 million light-years from us even in
a starship that could travel at almost light speed it would take us 2.2 million
years to get there the farthest known galaxies from Earth is called M ACS zero
six four seven JD it lies at the staggering distance of
thirteen point three billion light years
when we look at the sky at night then some stars or galaxies that we see might
not even exist anymore and some stars are galaxies that we can't see might
exist but their light hasn't yet had chance to reach us and we'll only know
about them in the future
one last question how is light produced stars produce energy by nuclear fusion
reactions deep inside the Sun hydrogen atoms combine at very high temperatures
to make helium atoms as a result of this process large amounts of energy are
released and eventually escape into space in the form of x-rays ultraviolet
visible light infrared and even radio waves during solar flares the Sun Also
emits gamma rays fortunately Earth's atmosphere prevents much of this solar
radiation from reaching the surface 26% of incoming solar radiation is reflected
by the atmosphere and 18% is absorbed by the ozone layer only 56% of solar
radiation reaches the surface some of which is reflected back by ice or other
bright materials only 48% is actually absorbed by land or water solar
radiation that reaches the surface consists of about 53% infrared 44%
visible light and 3% ultraviolet most of the light that we see was born deep
inside the Sun and other stars traveled across great distances of space and
finally made it through the defences of Earth's atmosphere to reach our eyes the
end of its epic journey
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