A Flame test occurs when a metal ion is heated in a bunsen burner flame. The metal compound will emit bright light that is a different colour to the bunsen burner flame. One type of metal ion will only emit certain specific coloured light. This light (Emission Spectrum) can be analysed (prism or a diffraction grating) and the identity of the metal can be determined.
Remember when all the colours of the visible spectrum overlap, the result is white light. A prism can be used to split white light into all the different colours in the visible light spectrum. Water droplets from rain also produce a similar effect when a rainbow is seen. When a flame test is observed the eye detects a mixture of the specific colours. When Hydrogen gas is excited in a flame the overall colour appears to be pinkish, even though the main visible colours present are red, blue and violet.
The Hydrogen gas discharge tube appears to emit pink light. The pink light is analysed using a diffraction grating. The actual coloured light in the hydrogen spectrum can be clearly identified as red, blue and violet (the light seen through the framed grating at the right of the tube).
Click the link below to find out more about flame tests and emission spectra:
http://www.webexhibits.org/causesofcolor/3BA.html
When astronomers analyse the light emitted by stars they use absorption spectra. Absorption spectra give the same information as emission spectra. The difference is that the absorption spectrum has black lines imposed on a background that has all the colours of the visible light spectrum. These black lines exactly match the coloured lines that can be seen in an emission spectrum that has a black background (see the diagram below).
The emission spectrum of Hydrogen. From http://coolcosmos.ipac.caltech.edu
The absorption spectrum of Hydrogen. From http://coolcosmos.ipac.caltech.edu
Check out the link below that shows you a series of absorption spectra for different known elements and then challenges you to figure out the elements present in a mystery star from it’s spectrum. It’s fun!
http://www.learner.org/teacherslab/science/light/color/spectra/spectra_1.html
The Life Cycle of Stars:
Stars begin life as giant clouds of Hydrogen gas. Remember Hydrogen gas is the most simplest element it’s atomic number is 1, since it has only 1 proton in it’s nucleus and it is the most abundant element in the whole universe. As the temperature and energy of the gas increases the Hydrogen nuclei can fuse with one another to form Helium nuclei. This process is called nuclear fusion.
Stars with low mass, like our sun, can keep fusing nuclei up to Carbon. High mass stars have a different destiny. Gravity can continue to pull carbon atoms together and additional fusion processes proceed, forming oxygen, nitrogen, and eventually iron. When the core contains essentially just iron, fusion in the core ceases. This is because iron is the most stable of all the nuclei. It takes more energy to break up an iron nucleus than that of any other element. The fusion of elements with larger nuclei than Iron would require an input of energy rather than the release of energy. Once energy is no longer emitted from the core of the star, in less than a second, the star will collapse. This leads to a chain of events that causes the star to explode. This is called a supernova explosion.
During the unstable conditions of the supernova explosion, elements heavier than iron will be formed. A shock wave propels these elements out into space. The material that is exploded away from the star is known as a supernova remnant.
When Moby wrote the song “We are all made from stars” – he wasn’t joking! All of the atoms that you are comprised of were once either formed inside a star or created when a star exploded and threw it’s atoms across the universe. Somehow these atoms made it to earth and have got together and formed bonds that have enabled them to be in a stable state – the result is a living thing, a human being, you!
See the link below to learn more about the lives of stars (the ones in outer space – not the ones in Hollywood!)
http://imagine.gsfc.nasa.gov/docs/teachers/lessons/xray_spectra/background-lifecycles.html
The Death of Stars:
A supernova is an exploding star. When I was at secondary school in 1987, a supernova explosion was detected in the sky. The cool thing about this supernova was that it had actually occured hundreds of years earlier but it had taken that long for the light that was created at the time of the explosion (supernova remnant) to finally travel all the way to earth. I wonder how many stars there are, that we think we can see but they have actually exploded and we don’t know about it because the light hasn’t got here yet.
Find out more about Supernovae – click on the link below:
http://hubblesite.org/reference_desk/faq/answer.php.id=30&cat=stars
What is Dark Energy?
Sounds sinister doesn’t it! But dark energy is a hypothetical exotic form of energy that supports the idea of an expanding universe.
Why is the idea of an expanding universe important?
Dark energy supports Hubble’s theory of an expanding universe. Hubble formulated his theory after making observations back in the 1920s. The idea of an expanding universe is one of the major pieces of evidence for the Big Bang theory.
How much dark energy is there?
Current theories suggest that around 74% of the total mass-energy of the universe is dark energy.
Some of the evidence for dark energy comes from Supernovae:
Recent observations of supernovae reinforce the theory that the universe’s rate of expansion is increasing. Objects that emit light waves that are moving away from planet earth will appear to have larger wavelengths than a stationary source of light (Doppler Effect). This is a similar phenomenon to how a police or ambulance siren’s pitch is different when it is moving away from an observer to when it is stationary. This effect is called a red shift because red light has larger wavelengths than other visible coloured light. Conversely if a source of light was moving toward earth the wavelengths would be blue shifted or decreased in size in relation to a source that is at rest.
This diagram shows how the absorption spectra can shift with respect to the spectrum whose source was at rest. From http://snap.lbl.gov/images/redshift.jpg
Since supernovae are red shifted this means that they are moving away from their previous positions in space. The amount of red shift can be used to find the speed of the original exploding star.
Dark energy is needed to explain observations about the geometry of space and the total amount of matter in the universe. Measurements of the amount of Cosmic Microwave Background (CMB) radiation suggest that the shape of the universe is flat. A flat universe leads to a total amount of matter in the universe of about 30%, as measured by the CMB. This matter includes baryons (protons and neutrons which make up atomic nuclei but there are many other unstable baryons too) and dark matter (hypothetical matter that does not interact with the electromagnetic force, but whose presence can be inferred from gravitational effects on visible matter). This implies the existence of an additional form of energy to account for the remaining 70% total mass-energy system of the universe. The most recent observations are consistent with a universe made up of 74% dark energy, 22% dark matter, and 4% ordinary matter.
To find out more about how supernovae mesurements support the Dark Energy theory and also Einsteins ideas check out the link below:
http://www.cosmosmagazine.com/node/2190/full
Brian Schmidt from the ANU, Canberra, was mentioned in the above Cosmos article. See his website by clicking on the link below:
http://www.mso.anu.edu.au/~brian/
Brian was co-awarded the Nobel Prize in Physics in 2011 for this work.
http://www.nobelprize.org/nobel_prizes/physics/laureates/2011/info_publ_phy_11_en.pdf
http://www.nobelprize.org/nobel_prizes/physics/laureates/2011/sciback_fy_en_11.pdf
http://www.nobelprize.org/nobel_prizes/physics/laureates/2011/schmidt-interview.html
February 7, 2011 at 4:39 am |
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