The electromagnetic spectrum and astronomy - our Solar System, cosmology, nuclear fusion and the life cycle of stars

Doc Brown's Physics Revision Notes

Suitable for GCSE/IGCSE Physics/Science courses or their equivalent

See also The Big Bang Theory of the Universe

 This page will answer many questions e.g.

 How has the explanation, theory and model of the Solar System evolved through time?

 What is nuclear fusion in stars?

 How have telescopes and photography helped us explore and understand the features of the Universe?

 What is the life cycle of a star?



Visible light and the Solar System

history of astronomy, Solar System models, cosmology, usefulness of telescopes and photography

  • 1.1 Be able to describe how ideas about the structure of the Solar System have changed over time, including the change from the geocentric to the heliocentric models and the discovery of new planets.

    • The geocentric model: The sun, moon, planets, and stars ie everything, all orbited the Earth in a series of concentric circles.

      • This model originates from ancient Greek civilisation 2000-2500 years ago and lasted for 1500-2000 years.

    • The heliocentric model: The Earth and other planets orbited our sun -then considered as the centre of our universe.

      • Astronomers such as Copernicus working in the mid-16th century, were making observations and calculations to explain the movement of the planets without the geocentric model and that a heliocentric model fitted the data better.

        • Copernicus published his heliocentric theory and calculations in 1543, just in time, two months before his death!

      • The Catholic Church was not too impressed by the scientific model challenging the religious view of how our 'universe' works.

    • Our contemporary model: The 8 major planets, minor planets and asteroids orbit the Sun in slightly elliptical orbits (our 'Solar System'), but our Sun is just one of millions-billions of stars in our galaxy (we see part of it as the 'Milky Way') and in turn the observable universe itself contains billions of other galaxies.

  • 1.2 Be able to show an understanding of how scientists use waves to find out information about our Universe, including:

    • a) the Solar System - the Sun and orbiting planets and asteroids

      • The movement of the planets and asteroids has been observed from visible light (reflected sunlight) for thousands of years, initially with the naked eye and from the early 16th century onwards, with telescopes.

      • With modern techniques, the Sun can be observed by detecting emissions in various regions of the electromagnetic spectrum eg infrared, visible light, ultraviolet, X-rays and even gamma ray emissions.

    • b) the Milky Way - the view looking through our own galaxy

      • Until relatively recently, the Milky Way galaxy, has been observed with the naked eye and then telescopes on Earth, but now it can be viewed through powerful telescopes on satellites eg the Hubble Space Telescope. Our galaxy, and for that matter distant galaxies, can be continually observed using everything from giant radio telescopes, huge optical\visible light telescopes to gamma ray burst detectors.

  • 1.3 Be able to discuss how Galileo’s observations of Jupiter, using the telescope, provided evidence for the heliocentric model of the Solar System.

    • Galileo, in the early 17th century, working with the newly invented telescope, found his view of the 'universe' in conflict with that of the Catholic Church, especially after discovering moons orbiting around the planet Jupiter, which meant not everything orbited the Earth and the geocentric model was flawed.

  • 1.4 Be able to compare methods of observing the Universe using visible light, including the naked eye, photography and telescopes.

    • In observing the night sky, the naked eye, apart from aesthetic appreciation, has been largely replaced by photography, usually coupled to a telescope.

    • However, historically, stars, planes, comets, our Moon have all been successfully discovered, observed, mapped and plotted via naked eye observations and astronomical tables of data assembled.

    • Distant stars can be seen because they are so hot and powerful emitters of electromagnetic radiation eg visible light.

    • Telescopes off much better light gathering power than the naked eye and the lens and lens-reflecting mirror systems can produced greatly magnified images and can peer into deep space totally inaccessible to the naked eye.

    • Photographing the same patch of sky and comparing images from one night to another can show up whether an object is moving eg asteroid or comet or some new star appearing or an old star exploding in a massive supernovae explosion,.

    • So, anything that changing that reflects or emits visible light can be detected and by using long-time exposures you can detect very faint very distant objects.

    • The result of all these historical and continuing contemporary observations with telescopes of all kinds is to give us a pretty good picture of the observable universe, even if we don't fully understand how it all works!

  • 1.9 Be able to describe how a reflecting telescope works.

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Nuclear fusion in stars and the life cycle of a star

nuclear fusion life cycle of stars, protostar, red giant, super red giant, supernova, black hole neutron star, white dwarf black dwarf

  • a) Know and understand that nuclear fusion is the joining of two atomic nuclei to form a larger one.

  • b) Know and understand that nuclear fusion is the process by which energy is released in stars.

  • c) Know and understand that stars form when enough dust and gas from space is pulled together by gravitational attraction.

    • Know that smaller masses may also form and be attracted by a larger mass to become planets around a star (a much larger mass).

    • You should be able to explain why the early Universe contained only hydrogen but now contains a large variety of different elements.

  • d) Know that during the ‘main sequence’ period of its life cycle a star is stable because the forces within it are balanced.

    • The term ‘radiation pressure’ will not be required.

  • e) Know and understand that a star goes through a life cycle.

    • Know that this life cycle is determined by the size of the star.

    • You need to be familiar with the chart below showing the life cycles of protostars and main sequence stars about the same size as the Sun or stars bigger than our sun, involving a Red Giant, Super Red Giant, White Dwarf, Black Dwarf, Supernova, Neutron Star, Black hole.

  • f) Know that fusion processes in stars produce all of the naturally occurring elements.

    • Know that these elements may be distributed throughout the Universe by the explosion of a massive star (supernova) at the end of its life.

    • You should be able to explain how stars are able to maintain their energy output for millions of years.

    • Know that elements up to iron are formed during the stable period of a star.

    • Know that elements heavier than iron are formed in a supernova.


See also The Big Bang Theory of the Universe

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Waves - electromagnetic radiation, sound, optics-lenses, light and astronomy revision notes index

General introduction to the types and properties of waves and how to do wave calculations, ripple tank experiments

Illuminated & self-luminous objects, reflection of visible light, ray box experiments, ray diagrams explained, uses of mirrors

Refraction and diffraction, the visible light spectrum, prism investigations, ray diagrams explained

Electromagnetic radiation, sources, types, properties, uses and dangers

The absorption and emission of radiation by materials - temperature & surface factors

See also Global warming, climate change, reducing our carbon footprint from fossil fuel burning

Optics - types of lenses (convex and concave), experiments and ray diagrams

The visible spectrum of colour, light filters and explaining the colour of objects

Sound waves - properties explained, uses of sound including ultrasound, earthquake waves

See also more detailed notes on The Structure of the Earth and earthquake waves (seismic waves)

The electromagnetic spectrum and astronomy - solar system, cosmology, nuclear fusion and the life cycle of stars

The Big Bang Theory of the Universe, the red-shift and microwave background radiation


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