|THE GREAT COURSES
DVD LECTURE SERIES
|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.
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.
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.
Professor Alex Filippenko.
|LECTURE ONE. 12 April
Day and Night Skies Across all Distances.
Celestial sphere - the 'dome'
that we percieve when we look skyward.
And a matter of notation (not mentionedin
|IMPORTANT CONCEPTS TO REMEMBER
Light years and light speed.
Atmosphere - to remember.
What's in a zero or two.
Terms to research and remember: supernova, nebulaegalaxy, Milky Way, light year, astronomical unit, Magellanic Clouds, gamma-ray burst, levels of atmosphere.
Questions to consider:
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?
|LECTURE TWO. 19April
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.
|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:
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.)
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 ?
|LECTURE THREE. 26
The Rainbow Family - Sunlight and Water
Concepts why we have a rainbow:
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:
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.