THE GREAT COURSES
DVD LECTURE SERIES
 
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Lecture series are viewed on a large TV screen at the Yarram Country Club each Tuesaday at 1.00pm.
Each session goes for about 30-40 minutes. We generally stay for a chat afterwards.

 
 
We own the following lecture series.
 
THE OTHER SIDE OF HISTORY: DAILY LIFE IN THE ANCIENT WORLD NOW ON
SKYWATCHING: SEEING AND UNDERSTANDING COSMIC WONDERS VIEWED
THE GREAT TOURS: GREECE AND TURKEY, FROM ATHENS TO INSTANBUL VIEWED
A HISTORY OF EUROPEAN ART 
YOUR BEST BRAIN 
THE NATURE OF EARTH: AN INTRODUCTION TO GEOLOGY
GREAT AMERICAN MUSIC: BROADWAY MUSICALS

 
 
 
THE GREAT COURSES - DVD LECTURES

We have started our DVD lecture series.
On Tuesday 12 April, at 1.00pm, at the Country Club, we started our post-graduate degree in Astro-physics and Astronomy, with the first of the DVD-based lessons on the subject - Skywatching: Seeing and Undestanding Cosmic Wonders. There are twelve lectures of 45 minutes each. At the first session we will decide how we will logistically set out the course - possibly a fortnightly session. Perhaps we will have a 45 minute lecture session followed by a 15 to 30 minute discussion.  Hopefully the DVDs provide a true lecture environment and not the dumbed-down 'scientific' docos that are frequently screened on SBS. So come along with a truly open mind that sets aside our every day concepts of time and space and appreciates the size of a quark at a trillionth of a millimetre, of how far a light year is, that a millionth of a second is indeed significant if we are looking at the Big Bang, and that matter the size of our Earth could be compressed.into the size of a golf ball. And please note - this is not a course for 'academics' and the university trained. It is for us ordinary folk who just want to know a bit more of what is happening around us.  This should be really good fun, and extremely interesting.
 

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A History of European Art: 48 lectures each of 30 minutes.
The Great Tours: 24 lectures of thirty minutes each.

See above in LATEST NEWS AND MEETINGS for more details. The next lecture series is soon to start. 

IMPORTANT
At the General Meeting on Monday 9 May, it was decided that we would continue our excellent lecture series with a course in either A History of European Art, or The Great Tours: Greece, Turkey, Athens to Instanbul.One of these series would he held at 2.00pm on a Tuesday at the Country Club - that is, after the Skywatch session. Members will/have received an email seeking their preference from these two excellent series, after which a start date will be announced. Members can thus attend one or both sessions on a totally diffeent topic on the same day. Please make your choice and respond to Jacqui's email.

This new lecture series will start at 2.00pm on Tuesday June 21. (Not June 24 as per Jacqui's email). Which series? - to be advised.
 


 
 
 
Some notes:

SKYWATCHING: 
SEEING AND UNDERSTANDING COSMIC WONDERS

Professor Alex Filippenko.


 
 
LECTURE ONE.  12 April 2016
Day and Night Skies Across all Distances. 

Celestial sphere - the 'dome' that we percieve when we look skyward.
The zeniith is the piiunt directly above you; the horizon is the visual line where the celestial sphere 'touches' the ground. 
The horizon (over a flat surface such as the sea) can be calculated by the equation:
Distance to horizon = (the square root of the visual height from your ground surface) times 1.2  [Note: This works fine for observations as sea level, looking at an horizon between sea and the celestial sphere. Strictly speaking, the distance to horizon is the height anywhere on earth from sea level, if looking toward a sea level (or low flat land) horizon.
The blue of the sky is due to sunlight reflecting off air molecules. Why blue? See next Lecture - its (mainly) to do with the wavelength of the 'colours' of light.
Remember the levels of the atmosphere: the troposphere that we live in, up to around 12 km; the stratosphere from 12 to 50 km which includes the Ozone Layer that we hear about, near the top of the statosphere; the mesosphere continues up to 100 km; and then the all important ionosphere with its ionized state and magnetic field. 
Statistics: The moon is 384,000 km from earth. The sun is 93 million miles away - thats nearly 150 million km. [Note: Generally we speak of distance in the imperial measure, that is miles. Because of the vast distances in 'space', we also use other terms such as AU - this distance between the Earth and Sun; or Light Years which is based on the time that light travels in one year. This is 186 miles a second which is about six trillion miles - ie 6,000,000,000,000 miles. (I think I have the number of zeros right!). So a star 6 light years away is 36 trillion miles away. Note: Light Years is a measurement of distance, not time.
The closest star is Alpha Centauri at 25 trillion miles distance -  that about 4 light years away. The brightest star we can see is Sirius at about 50 trillion miles. 
The 'visibility' of a star is based on its luminosity (how bright it really is) and its distance from us. How we see it is based on the inverse square law of light - so two stars of the same luminosity - star A at x distance from us, and star B at twice that distance, would result in star A appearing to be four times as bright as star B. The actual equation is: brightness = luminosity divided by (4 x pi x d-squared).
How far can we see? The explosion of a super-nova (more on them later) can be seen from 100,000 light years away. 
I think it was Carl Sagan who said 'we are made of the stars'. Indeed that is so, as a result of the heavier (than hydrogen and helium) elements being created when a supernova explodes and matter is blasted into outer space. 

And a matter of notation (not mentionedin the lectures). 
If we refer to our shining star in our solar system we write Sun with a capital S. But another other star, or sun, is written with a small s. We refer to our satelite as the Moon - but all other moons are with lower case. Likewise we ofter refer to our planet as Earth, but the earth can also mean the ground we walk on. Theer is no valid reference to 'earth' on any other celestial body. 
 

IMPORTANT CONCEPTS TO REMEMBER

Light years and light speed.
Light speed: 186 miles per second; 671 million miles per hour..
(300 km/s; 1100 million km/h). A light year is thus 6 million million miles (6 trillion) give or take a few yards. (Actually, it is 5.8786 x 10 to the 12th miles).
Within current scientific knowledge (thanks to Einstein) , nothing can travel faster than light. If a star is six light years away, it would take at least six years to reach there - but of course you wouldn't be able to according to Einstein. When you see the sun, in absolute time the sun has aleady disappeared eight minites earlier. If  Mars  were 200 million miles away and you could reach there at the speed of light, it would take about 18 minutes - but it will never happen. As you travel faster, you get heavier, or more specifically, your mass increases. At thew speed of light your mass would be infinite. More on that in later lectures no doubt.

The Sun.
Is 93 millions years away - approximately as it varies. It takes sunlight about 8.3 minutes to reach us. This distance is called an astronomical unit, AU. The moon is 384,000 km from earth.

Atmosphere - to remember.
Troposphere - that our home up to 12 km.
Stratosphere - includes the Ozone layer - and satellites.
Mesosphere - way up to 100km.
Ionosphere - not much hear, bordering 'outer space'. 

What's in a zero or two.
There was a time - indeed, still is - some confusion as to the terms billion, trillion etc. The USA uses the currently most acceptable nomenclature but in the near past, Britain and parts or Europe especially, were different. Without going into history, the accepted unit nomenclature (and certainly as used in our lectures) is as follows. 
A million is of course 10 to the 6th, ie 1,000,000. (You know how the '6' is written I hope - I can't do it on this webpage - it is the small-written number next to the 10, like you would have the '2' in the number two squared). 
A billion is 10 to the 9th, ie a one followed by nine zeros is 1,000,000,000.
A trillion is 10 to the 12th - you can work that out. Let's not go beyond that as highter numbers (greatr than a million) and use with the exponential notations showing the number of zeros. 

Terms to research and remember: supernova, nebulaegalaxy, Milky Way, light year, astronomical unit, Magellanic Clouds, gamma-ray burst, levels of atmosphere.

Questions to consider:
Suggest work these out and discuss at the next meeting.

1.1 If a star we call Peter is one hundred time brighter than a star called Paul, but is ten times the distance (from Earth) than is Paul, what is the relative perceived brightness between the two?

1.2  In a model of the universe built here in Yarra, if the earth were the size of a golf ball (and thus a black hole, more on that later), where would you find our moon - could the model fit in a normal lounge room? And how would you represent the moon with a household object?

1.3 What enables us to see a perfect eclipse if we are at the right place on earth, where the moon exactly 'covers' the sun?

ANSWERS


 
 
 
LECTURE TWO.  19April 2016
The Blue Skies, Clouds and Lightning 

The Earth's atmosphere decreases in density with increasing height. The atmosphere is almost transparent and thus colourless. The almost gives us the blue sky. Most sunlight - which is white (not yellow!) - reaches the earth, but some light (photons) are reflected from the atoms (and other minute particles such as dust) and scatter across the sky, often bounciing off other atoms before reaching earth - specifically, before reaching our eyes. 
So why is the sky blue? For some reason or other, the molecules reflect more of the shorter wavelengths of light than the longer ones, so blue is reflected more-so than red, five times as much in fact. 
Why is there a halo around the sun? This is due to aerosols - tiny particles of gas or liquid that scatter sunlight as white light The halo effect around the bright sun is due to the aerosols scattering white light. The halo is called an aureole
Polarization of light - this is a tricky one. Polarization is a scientific concept - it involves light, radiation, or magnetism moving in specific directions - specifically, oscillating (the 'wave') perpendicular to its direction of travel. It's hard to get the mind around this one, but is is easy to experience if you use a pair of polaroid sunglasses. Get two pairs, and rotate one around the other and see what you see!  Light from the sky is partially polarised, and can be easily further polarised - ask any serious photography. 
Clouds are droplets of water or ice crystals. They scatter all wavelengths of light equally so appear white.  Clouds are produced when moisture in the air condenses, forming either water droplets or ice crystals. Condensation (it rains) occurs when the air temperature falls below dew point - because cold air cannot retain as much moisture as warm air. Like life species, clouds have similar classification nomenclature (but no so extensive) to define each 'type', called a genera. The main genera  are cirrus, stratus and cumulus. Within these 'top orders'  are 'species' such as cirrostratus, stratocumulus etc etc. which can further be defined  by a sub-species defining its shape, density and thickness. It's an intense study in itself.- called nephology. 
We learnt about lightning - the study called fulminology. Lightning is formed from the ionization of air: collisions among particles strip electrons off some atoms, leaving them positively charged and providing a negatively charged excess of electrons on other particles. In this way, a lightning bolt is a greatly scaled-up version of the discharge you experience with static electricity in your home. It mainly occurs in cumulonimbus clouds. Thunder occurs when the electric current in a lightning bolt suddenly heats the air in the discharge channel to temperatures of about 30,000-50,000 degrees Fahrenheit, causing it to glow by incandescence. This superheated air expands supersonically and sends a shock wave through the atmosphere; that's what we hear as thunder.
 

IMPORTANT CONCEPTS TO REMEMBER

The air in our atmosphere is composed of molecules of different gases. The most common gases are nitrogen (78%), oxygen (about 21%), and argon (almost 1%). Other molecules are present in the atmosphere as well, but in very small quantities, including water vapour.

Light is an electromagnetic wave, with wavelength (the distance between the troughs), the frequency (how fast the waves zip by), and the amplitude (how high is the wave). 

The dew point (dew point temperature or dewpoint) is the temperature at which dew forms and is a measure of atmospheric moisture. It is the temperature to which air must be cooled at constant pressure and water content to reach saturation - and then it rains or forms 'the dew' on the ground.

The main cloud genera: 
cirrus: thin, high, wispy consisting of ice crystals.
stratus: horizontal layers or sheets , not too thick, of ice crystals or water droplets.
cumulus: puffy billowing clouds, high vertical component, of water droplets. 

To determine how far away the thunder is, work on the difference between seeing lightning and hearing thunder as being five seconds per mile or three seconds per kilometre. (Work this out for yourself based on what we learnt last session.)
 

Understanding question:
Suggest answer these and discuss at the next meeting.

2.1 Apart from the fact that we would not be here, what would you see if you looked up from an Earth without an atmosphere during the day? 

2.2 What does a photographer do to darken or enhance the sky? (No, using Photoshop is not the answer.)

2.3 Why was I excited when I saw an uncinus and a floccus the other day?

2.4 In which level of the atmosphere do we find clouds ?

2.5 Is there a similarity between clouds and fog ?

2.6 What is a contrail and how is it formed? (I photographed one this morning.)

2.7 What is the fear of lightning (and thunder) called ?

ANSWERS

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LECTURE THREE.  26 April 2016 
The Rainbow Family - Sunlight and Water

Concepts why we have a rainbow: 
(a) The speed of light is slower in glass and water than in air, and this causes the light to ‘bend’ or refract, when entering and exiting glass and water. 
(b) The speed of each wavelength (colour!) Of light varies slightly, ie violet fr example has a shorter wavelength and travels through glass and water slower than red light, so violet light is bent more.
(c) Sunlight entering a raindrop is both reflected and refracted - ie, some light bounces back, some light passed through and is ‘bent’ to various degrees depending on its wavelength, both on entering and exiting. Some light on exiting also gets reflected back into the raindrop.
(d) No two people see the same rainbow. It depends solely on the relative position of the person (ie the eyes) and the rainbow, that is, the relative position of the person to the line of refraction of the ‘rays’ of light - and in the same context, each individual raindrop is reflecting a different ray (colour) to each person.
(e) The maximum amount of refraction is 42 degrees (for red) and drops to 40 degrees for violet. 

These factors result in sunlight creating a coloured rainbow, with violet light being refracted less than red light and thus violet light appears lower in the rainbow than red light. This is always the case with a ‘primary’ rainbow. It is the other way round for a ‘secondary rainbow’ which may appear faintly behind the primary. 

The ‘spread’ of light in a rainbow, and as experienced with light through a glass prism, is called a spectrum. A spectrum defines a specific range of electro-magnetic wavelengths which define what we see with our eyes and in interpreted by our brain - what we actually see. The various wavelengths define the colour. Infra red and ultra violet as just the same electro-magnetic waves as our perceived ‘light’ but we cannot see them - our retinas cannot capture them in normal circumstances. 

The sky immediately above the rainbow is darker than the sky below the rainbow. This is due to the fact that light cannot refract more than 42 degrees (hence darker), yet all light refract to some degree less than 42 degrees, so the ‘bottom’ of the rainbow and its sky is lighter. 

A rainbow is actually a circle, or a cone to be more precise (as the ‘circle’ is only a perception by the one viewer whereas the rainbow exists as a cone to be seen as infinite ‘circles’ to be seen individually by an infinite number of people). If the observer is standing on or close to the ground, the cone, ie the ‘circle’ extends into the earth and thus cannot be seen. From the air however, a complete circle could be seen under the right conditions. 

Because of the laws of refraction indicated above, we cannot see a rainbow if the sun is more than 42 degrees above the horizon. If the sun is very close to the horizon, a pure semi-circle can be seen. And to see a rainbow (in rainy conditions of course) you must be between 40 and 42 degrees from the antisolar point. This is the direction in the sky directly opposite the sun - stand up, look at your shadow and image a line from the sun to your head. 

Also to be seen:
- a lunar rainbow (at the time of a full moon)
- fogbows - rainbows in fogs
- reflected rainbow (as seen reflected from a flat sheet of water).
- secondary rainbow - above the primary rainbow, with its colour band reversed, due to a secondary refraction within the raindrop - that is, light has ‘bounced’ within the raindrop and then exited. 

 


 
 

There are also rainbows called supernumerary bows which can be explained by a detailed look at the wave theory of light. It has to do with the wave formation of light, the ‘adding and subtracting’ of two waves. The lecture explains this but it required a good knowledge of the interaction of electro-magnetic waves. (In other words, I have not a clue what he is talking about - well, mainly).

The corona around the moon is caused by a similar diffraction of raindrops for rainbows, but in this case the diffraction corona requires tiny droplets of water or ice crystals inside clouds. (This can also occur around the Sun but don’t try looking for it unless equipped with the right sun-viewing glasses.) This is also related to the formation of cloud iridescence. 

The lecture also refers to a glory, a ring or set of rings on clouds in the direction opposite the sun. This is not to be confused with a Morning Glory, a rare cloud formation close to the ground, generally over sea, that looks like a long grey towel wrapped into a tight cylinder. A remarkable sight. (I saw one years ago at Narooma when on a boat). 
 

FACTS AND FIGURES

Rainbows are refracted light from raindrops (or through glass) with a degree of ‘bending’ light between 42 and 40 degrees into a spectrum. 

Raindrops are generally 0.1 to 5 millimetres in diametre (a millimetre is a thousands of a metre), although those forming rainbows need to be typically 1 to 2 millimetres. 
 

QUESTIONS TO PONDER

3.1 Suppose water droplets refracted all wavelengths of visible light exactly the same way - would rainbows still be seen. And what would they look like?

3.2 Would the appearance of a rainbow change with viewing through a polarizing filter?

3.3 Can we touch a rainbow? 

3.4 What else can cause a rainbow to be readily seen.