OU S194 Course Description|
NASA Mission to Mars
Mars global surveyor
The search for Beagle 2
Extrasolar Planets Encyclopaedia
Federation of Astronomical Societies
Galileo Journey to Jupiter
Hawaii Solar Astronomy
Search for extrasolar planets
The Solar and Heliospheric Observatory
Society for popular astronomy
UK Students for the Exploration and Development of space
University of Cambridge Institute of Astronomy
Yohkoh Public Outreach Program
Malin Space Science Systems - Images
Particle Physics and Astronomy Research
British National Space Centre
The Planetary Society
The Mars Society
Observing the Sun
Inside the Sun
Measuring the Sun
Survey of the Solar System
The view from the Earth
The planets and their major satellites
Evolution of the Solar System
Constellations and stellar distances
The colours of stars
Star birth and death
The fate of stars
Is there life beyond the Earth?
Life on Earth
Potential habitats in the Solar System
Potential habitats beyond the Solar System
The Milky Way galaxy
Clusters of galaxies
The expanding Universe
Distance, redshift and recession speed
The early Universe
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21 August 2006
I registered with this course because I need one more level 1 science shortie, to qualify for the new Certificate in Contemporary Science! I'm not going to start it until after the S330 ex*m though ..... Not sure I will manage the Planisphere ....
16th October 2006
AT LAST I have opened the book! I spent the afternoon reading through the first chapter (The Sun) - and looking at some very pretty pictures on the CD-ROM! I'll list all the chapter summaries here, although they are 'essential points', rather than any indepth summarisation.
The Sun is a star, emitting all types of eelctromagnetic radiation. The light that reaches Earth from the Sun comes mainly from the photosphere, although on its way to Earth it must pass through the chromosphere and the corona. Each of these parts of the Sun shows signes of magnetically driven activity.
Electromagnetic radiation consists of waves that can travel through empty space and cover a huge range of wavelengths.
The Sun is powered by nulcear reactions in its hot core which enable it to release energy steadily over thousands of millions of years. The energy released in the core is transported to the surface by radiation and then convection, passing through radiative and convection zones on the way.
The Sun and Moon have approximately the same angular size when viewed from the Earth.
The angular size of an object depends on its actual size and its distance from the observer.
The Earth is one of nine planets orbiting the Sun in the same direction, in nearly circular orbits, in roughtly the same plane.
The Sun, the planets with their satellites, and a range of small bodies collectively make up the Solar System.
To maintain any circular motion, a cetripetal (ie inwardly directed) force is required. The orbital motions of planets and satellites are maintained by the force of gravity.
The motions of the Earth, the Moon and the planets can explain the changing appearance of the night sky, the Moon's phases, the seasons and eclipses.
The planets in the Solar System (excluding Pluto) can be classified as either terrestrial or giant planets.
Asteroids (rocky) and comets (icy) are small bodies that formed in different regions of the Solar System.
Meteorites can provide information about asteroids and the surfaces of other planets as well as about conditions during the formation of the Solar System.
The Solar System is thought to have formed from a disc of gas and dust orbiting the Sun - the solar nebula. The general properties of the planets are determined by the distance from the Sun at which they formed.
The surfaces of planets and satellites are moulded by many processes. Space exploration has vastly increased our knowledge of the planets and their evolution.
Large numbers can be written in compact form using scientific notation.
The positions of stars can be specified using celestial coordinates
Planispheres and planetarium software can be used to determine which stars are visible at any date and time from any given location.
A wide variety of celestial objects can be seen with the unaided eye.
Stars may be arranged in constellations, but these do not represent physical groupings of stars.
By comparing the apparent brightness of stars, astronomers can deduce their distances; broadly speaking, the fainter a star appears, the greater its distance.
The light year is the distance light travels through space in a year; stars typically lie many light years from one another and from Earth.
The colours of stars indicate their temperatures; blue-white stars are hottest, while reddish stars are cooler.
Spectral lines give information about the substances that compose a star.
Small numbers can be written in a compact way using scientific notation with negative numbers for the powers of ten.
The uncertainty in a measurement is an etsimate of the error (the difference between the measured and true values).
Star formation begins when a molecular cloud contracts under gravity.
A contracting fragment of a cloud becomes a protostar, its central temperatures incresing until they are high enough for nuclear reactions to begin.
A main sequence star shines steadily for billions of years while consuming its hydrogen in nuclear reactions.
When its hydrogen is exhausted, a main sequence star swells to become a red giant or a supergiant.
A red giant ejects a planetary nebula and ends as a white dwarf.
A star that begins with over 11 times the Sun's mass ends in a violent supernova explosion, leaving an extended remnant and possibly either a plusar or a black hole.
Material ejected from stars eventually cools and may enter further cycles of star formation.
All life-forms on Earth are based on complex carbon compounds, and require liquid water during at leat part of their life cycles.
In looking for extraterrestrial life, attention should focus on places where huge, complex carbon compounds and liquid water could exist, the possible existence of liquid water being sufficient in practice.
Within the Solar System, Mars and Europa are the best candidates for finding extraterrestrial life. At the surface of Mars today water can persist only as a solid, and there is no evidence for life on the Martian surface. There might be life deep underground, where water could exist as a liquid. In the distant past, conditions on Mars were different, and liquid water could have persisted at the surface. Life might have evolved then, and so we might find fossils.
Europa is a rocky world overlain by an ocean of water and topped by a thin crust of ice. The water is maintained as a liquid through tidal heating. There might be aquatic life-forms in the oceans.
Beyond the Solar System astronomers look to the planets for other stars. Many nearby stars are already known to have planetary systems. This represents a few per cent of the nearby Sun-like population, and this proportion can only grow. As we discover more exoplanets, their spectra will enable us to look for signs of life.
The Sun is one of about 1011 stars that make up the Milky Way galaxy. The Sun is part of a disc of stars, 100 000 light years in diameter, with a bar-shaped bulge at its centre. This is embedded in an extensive stellar halo. However, all these visible components of the Milky Way are believed to be dominated by an even more extensive halo of dark matter that accounts for teh great majority of the Milky Way's mass.
Most galaxies can be classed as elliptical, lenticular, spiral or irregular, according to their observed shape.
The distances of galaxies can sometimes be gauged from their angular sizes.
The Doppler effect can be used to measure the movements within galaxies. The discs of spiral and lenticular galaxies show orderly rotation. Elliptical galaxies show little or no overall rotation.
Active galaxies emit far more electromagnetic radiation than can be accounted for by their stars and ISM alone. They are believed to contain supermassive black holes. The behaviour of matrial falling into those black holes is primarily reponsible for the additional radiation emitted by active galaxies, and for its variability.
Galaxies are gathered together in space in clusters and superclusters. The superclusters are separated by voids, giving rise to a large-scale structure that is similar to that of a sponge. Superclusters are hundreds of millions of light years across. Each supercluster therefore occupies a small but significant fraction of the volume of the visible Universe.
Hubble's law describes a proportional relationship between redshift and distance for remote galaxies. Its discovery provided a simple means of determining the distances of galaxies, and evidence of the uniform expansion of the Universe on a large scale.
The modern view of cosmic expansion is that it involves the expansion of space in a way described by general relativity. This appraoch provides a natural explanation of Hubble's law.
Hubble's law may also be expressed in terms of a proportional relationship between the current distance of a galaxy and its current recession speed. Recent measurements of Hubble's constant indicate that galaxy recession speeds currently increase by about 22 milometres per second per million light years, with an uncertainty of about 10%.
Evidence indicates that the expansion of the Universe began about 13.7 billion years ago in an event known as the big bang.
As the Universe expanded and cooled, the nuclei of light elements were formed with predictable abundances. Later the Universe became transparent, releasing the radiation that became the observed cosmic microwave background radiation.
Departures from uniformity in the cosmic microwave background radiation are related to the formation of superclusters and voids. They provide detailed information about the age and composition of the Universe, and confirm the presence of the little understood dark energy that is thought to account for most of the energy in the Universe.