Stress Patterns

Here are some more pictures taken at the ASE show. 

These show the stress patterns which are visible in our set square after it is exposed to polarised light, for these images we have used a polarised light source from a standard LCD computer screen instead of our normal lightbox.

The LCD screen has a polarising film in it at 45 degrees to the vertical so only a single sheet of polarising film is needed to produce an effect.

Set square with out Polarising Film.

Stress patterns within the set square viewed through a sheet of Polarising Film.

Amazing World

I have found an amazing video cropping up on my news feed a lot in the last few days and decided to take a look at it.
Well I cant keep it all to myself it is an amazing piece of footage from the International Space Station. 


What a truly amazing planet we live on.


I do just wish this as a little slower so I could appreciate the detail a little more.



Earth | Time Lapse View from Space, Fly Over | NASA, ISS from Michael König on Vimeo.


Time lapse sequences of photographs taken by Ron Garan 
fragileoasis.org/​bloggernauts/​Astro_Ron and the crew of expedition 
28 & 29 onboard the International Space Station from August to October,
2011




List of clips:
1. Aurora Borealis Pass over the United States at Night
2. Aurora Borealis and eastern United States at Night
3. Aurora Australis from Madagascar to southwest of Australia
4. Aurora Australis south of Australia
5. Northwest coast of United States to Central South America at Night
6. Aurora Australis from the Southern to the Northern Pacific Ocean
7. Halfway around the World
8. Night Pass over Central Africa and the Middle East
9. Evening Pass over the Sahara Desert and the Middle East
10. Pass over Canada and Central United States at Night
11. Pass over Southern California to Hudson Bay
12. Islands in the Philippine Sea at Night
13. Pass over Eastern Asia to Philippine Sea and Guam
14. Views of the Mideast at Night
15. Night Pass over Mediterranean Sea
16. Aurora Borealis and the United States at Night
17. Aurora Australis over Indian Ocean
18. Eastern Europe to Southeastern Asia at Night

What do the spectrums mean?

Previously I have shown images that I have taken of the spectrum captured using my home-made spectrograph and plain and simple diffraction grating slides, but what do the images captured actually mean?


I will start by explaining what visible light is in relation to the electromagnetic spectrum then


Visible light:
This is one section of the Electromagnetic (EM) spectrum which is visible to the human eye. Light (and other electromagnetic radiation) travels as a wave but unlike sound energy, which vibrates the air particles to transport the signal away from the source, it does not need particles to travel through since it is a vibration of the magnetic and electric fields. This enables light to reach us from the sun, through the vacuum of space. 

This image shows the different wavelengths of the visible light spectrum. Red light has a lower frequency (therefore a larger wavelength ~700nm) and violet light has a higher frequency (smaller wavelength ~400nm), outside of these wavelengths the human eye is unable to pick up the signal contained by these waves. 


Colours are perceived by the eye due to different proportions of the different wavelengths being absorbed and reflected by different surfaces. A surface which appears Red will be reflecting the EM radiation which corresponds to the red section of the spectrum whilst absorbing the other wavelengths. 
Colours which are not a direct wavelength colour (Red, Orange, Yellow etc) can be made up by mixing light of different wavelengths. 


'White light' is made in a similar fashion and is composed of light of all the different wavelengths. 


Images of the spectrum:


The fact that white light is made up of the whole spectrum can be shown simply by shining a light through a prism which uses the difference in densities of the glass and air to bend the light. Light of different wavelengths reacts to the change in densities by a different amount so they bend at different angles causing the spectrum to spread out. 

This process is replicated in the diffraction grating but in a way that means it is possible to have a 'flat' material rather than the traditional bulky prism. 


The images I took previously of the spectrum from an incandescent bulb shows the same complete coverage of the spectrum and all at a similar intensity.

Whereas the spectrum of the energy saving light bulb shows bands of higher and lower intensity throughout the visible spectrum. 

The differences between the two spectra are due to the processes that the bulbs use to create 'white light' (I will discuss this in a later post). But what do the actual spectra mean?


Well, certain elements will give off light at specific wavelengths, called an emission spectrum, which is controlled by the actual structure of the atom in question. 


here is an example of an emissions spectrum for Carbon:

This shows the intensity peaking at specific wavelengths. Using spectroscopy scientists can ideantify the elements in a substance. This is mostly used in astronomy, where scientists will use the emissions spectra for stars or distant galaxies to identify what elements are present and giving off light.

Photos of Light spectrum through diffraction grating

In addition to my Polarising film set up I am trying to create a set up to show how light is split when passing through diffraction grating. So I picked up a grain of wheat bulb and set about trying to work out how would be best to show this.
Unlike my polarising film photos the set up was not already created, so these photos are from my first round of trials and there will be more when I have managed to incorporate the modifications that showed to be necessary from this round.

I did initially try a round of photos with an E10 bulb and a white background but this was too large a light source and the white background meant that it washed the colour out of the spectrum and provided problems when trying to clean up the images.

So my first modifications resulted in using a black table as a background and taking the photos in the dark (except for the bulb) to reduce the amount of background light, and using a grain of wheat bulb since this would produce a much smaller light source.
I am yet to decide if taking photos in a dark room is a good idea or not since when the light source is in the photo it 'burns out' due to being so much brighter than the surrounding image.


This image shows how bright the light is but also shows the colours produced quite well.

This was only the second photo I took with this set-up and here I will have to apologise for the quality of the photos since it was only a trial they are only taken using my iPhone camera.




This shows how the main part of the spectrum is 'burnt out' since it it much brighter but it also shows the range of colours that the light produces and shows the start of a second 'tail' out side of the initial spectrum. Here the light source is to the left of the image.

Another problem that shows up on some of these images in that the Diffraction Grating that I used was just held by me in one hand so it had a tendency to bend resulting in bent spectrum lines this will be rectified in future photography sessions by mounting the diffraction grating before using it. I will also mount the camera since these images are taken in the dark resulting in a long exposure time so to create a higher quality photograph mounting the camera would reduce the blur created by movement of the camera.

The first set of images were taken with either 500 or 1000 lines/mm Single Axis Diffraction grating but I also had 532 lines/mm Twin-Axis Diffraction Grating to play about with and this produced some much more interesting images



Here the spectrum is split as it was before but due to the diffraction grating having two axis the light is split in many directions producing this interesting star effect.

To view more of the initial photos see them here