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I - Factary




In order to describe the illumination of a scene produced by a source of light we need to use an appropriate unit (in the same way we measure distance in metres and time in seconds). Scientists use a unit called a LUX to measure and describe Illumination. On Earth when the Sun is overhead it can create an illumination of about 100,000 lux. On a cloudy day we might only get 35,000 lux.


However, an adequate illumination for normal working is reckoned to be only about 300 lux. It seems that even on a cloudy day the Sun produces over 100 times as much light as we actually “need”! The minimum illumination for viewing objects without too much difficulty is around 120 lux.
Most people are quite comfortable watching a floodlit sporting event at night. The lighting for such events is designed to give an illumination on the field of between 200 and 500 lux, depending on the sport. After the game if you were to take a romantic walk home by moonlight, you would be coping with an illumination of only 0.1 - 0.2 lux!


What these numbers show is the amazing ability of the human eye to adapt to an enormous range of light levels .


You will also notice that we have avoided using the word “brightness” even though it is normal and natural to ask “how bright is the Sun?” or “how bright is that lamp?” This is because scientifically we reserve the word “brightness” to describe the effect the brain perceives when light shines into our eyes – and that is a very complicated process. As we saw above, the eye and brain allow us to cope in our everyday lives with a huge range of illumination, but it is not a very good system for quantitatively measuring that illumination. We can accurately say that two lamps appear to produce the same illumination (they appear equally bright to us) but it is impossible for us to say if one illumination (produced by a lamp, say) is twice as strong as that produced by another “brighter” lamp. To answer that we need instruments that measure lux!



Imaginative answers


One of the things that can be really boring about science, especially at school, is that most times (well in exams especially) you are supposed to churn out the same old answers to the same old questions, just to get the marks. Think how much more fun it would be if you were allowed to think of imaginative answers for a change, and got credit for them! We don't mean just silly, non-sensical answers, although they can be useful in exploring a topic, but ones that show you know some science even though your ideas may not necessarily be all that practical.


BrainiacStart a campaign against always having to give the standard 'gimme-a-mark' type answers!


An example we like and which we heard of many years ago was connected to a physics question about pressure in the Earth's atmosphere. Pupils had been learning about how atmospheric pressure decreases with height (see Pascal's factary entry) - the pressure at the top of a mountain is a lot less than at sea-level for instance. So in principle, if you have a barometer (an instrument for measuring pressure), then by measuring the pressure change from the ground floor to the top floor of a building, you could calculate the building's height. This was the answer examiners wanted to hear when they set the following question:


Q: Explain how, using a mercury barometer, you could determine the height of a multi-storey building.


One student is reported to have given the following answers:


Answer 1: I would get a long piece of string, as high as the building, and tie the barometer to one end. I would then go to the roof of the building and use the string and barometer as a large pendulum. By measuring the time the pendulum took to swing I would calculate the length of the piece of string.


Good physics! The period, T, ( the time in seconds for one complete swing) of a pendulum with length L metres is given by 2π√(L/g), where g is the acceleration due to gravity and is approximately 10 m/s². If the period of the pendulum was measured to be 10.0 seconds, the student would calculate the height of the building to be 25.3 metres. That would probably be a much more accurate answer than he would get by trying to measure the change in pressure from ground floor to top floor!


Answer 2: I would go to the top of the building and drop the barometer over the side. By timing how long it took to reach the ground I could calculate the height of the building.


Good physics again! Ignoring the effects of air resistance, if the barometer took T seconds to fall to the ground under the force of gravity, then the distance it fell is given by D = 5T2 metres. The question didn't say you had to return the barometer in good shape! If the building really was 25.3 metres high, the fall time would have been 2.25 seconds.


Answer 3: I would find the caretaker of the building and offer to give them a really nice barometer as a present if they could tell me how high the building was.


Doesn’t contain any good physics, but a great answer all the same. We hope the student got full marks even without giving the expected answer since thinking of new and original solutions to problems sometimes opens up whole new areas of investigation.




Electromagnetic radiation with wavelengths longer than visible radiation but shorter than radio waves. Most infrared radiation is absorbed by the Earth's atmosphere and so most infrared astronomy must be performed from spacecraft.



In 1800, William Herschel described how the differently coloured filters, through which he observed the Sun, allowed different levels of heat to pass. He performed a simple experiment to study the "heating powers of coloured rays". He split sunlight with a glass prism into its different rainbow colours and measured the effect each colour had on a thermometer. He observed an increase in temperature as he moved a thermometer from the violet to the red part of the spectrum. Out of curiosity Herschel also measured temperatures in the region just beyond the red colour, where no light was visible, and to his surprise, he recorded the highest temperature there. He deduced the presence of invisible "calorific" or heating rays, that which we now call infrared radiation.




Scientists are a bit like detectives in a lot of respects. Both perform investigations to gather evidence from which they form conclusions. Without investigations we would never know how the universe works. This is how we gather data and decide what is a 'fact'. To a scientist a fact is only a fact if it stands up to being tested by experimentation. Also be careful with the word 'truth'. Scientists don't search for the truth, it's never quite as simple as that.


In schools we are taught how to investigate questions. Every investigation starts with a question and ends up with some kind of an answer. These are obtained through a process of scientific method that starts with the planning stage. This is where the question is broken down into manageable sections, predictions are made and a method of investigation is identified. Then comes the obtaining of evidence section. This can involve taking measurements or the observation of events, and testing the variable you wish to know about and its effects. Once results have been gathered they have to be analysed. This is where any patterns, relationships or facts are identified. Graphs are a good method of analysing results. Finally the evidence has to be evaluated. The results and conclusion are no good unless the readings are reliable and accurate.




An ion is an atom that has lost or gained one or more electrons and has become electrically positively or negatively charged as a result.


Electrons can be knocked away from atoms in several ways. Most often it happens when the temperature gets so high that the atoms are moving around so violently they bang into each other and during the collisions the electrons get knocked off. Sometimes the electrons can suffer a 'direct hit' from an energetic photon (packet of radiation energy) and that can also knock them out of the atom.



Normally an iron (Fe) atom has 26 electrons orbiting the nucleus. Conditions in the solar corona however are so hot that we usually observe the iron atoms when they only have between 13 and 18 of their electrons left. An iron ion with only 15 electrons left out of its original 26 is written as Fe+11 because 11 electrons have escaped and so it is left with a positive charge of +11.




The process by which ions are produced. This typically involves collisions with atoms or electrons ("collisional ionisation"), or by interaction with photons of electromagnetic radiation ("photo-ionisation").




The region of the Earth's upper atmosphere containing free electrons and ions produced by photo-ionisation. Because some radio waves can be reflected by the ionosphere (it acts like a giant mirror surrounding the Earth) it is used, even in these days of communication sateliites, to send radio signals around the Earth.The ionosphere can significantly influence the spread around the world of radiowaves with frequencies of less than about 30 MHz.


Study of the ionosphere is important for solar-terrestrial science, but it is also still important in the “real world” because it is used:


1) a lot by the UK Ministry of Defence for high frequency (short wave) communications because it's cheap and easy and doesn't depend on the availability or reliability of satellites.


2) by emergency services - e.g. for shipping (cheap and easy again)


3) by amateur 'radio hams'


4) by radio/TV broadcasts (including the BBC world service even though they now have 'local' transmitters around the world). An interesting hands-on type use is shown in this picture.


Ionosphere - radio map


This map shows you the best frequency to use for communications using the ionosphere. For efficiency it is best to use the highest frequency possible and the map shows you the highest frequency that the ionosphere will reflect. Depending on where you want to communicate with, the map allows you to choose the best frequency. Since ionospheric conditions change constantly, the map is updated several times a day.




The universe is made up of over 118 elements which are the basic building blocks of the universe. Each element is made up of just one type of atom. However, nature allows some variations in these basic atoms and we call these variations isotopes. Isotopes have the same numbers of protons and electrons as the standard atom, but they have different numbers of neutrons. As a result, they have a different atomic mass from the standard atom.


Here’s a great diagram of isotopes of hydrogen and carbon. It was created by Dr Freitas of Riverside Community College chemistry department.



BrainiacOne of the most famous uses of isotopes is in dating of old organic material using isotopes of carbon (C).


Most of the carbon in the Earth's atmosphere exists as 12C (called carbon twelve). That is to say it has 12 protons and 12 neutrons. However, 14C (carbon fourteen) is a radioactive isotope with 12 protons but 14 neutrons, which is constantly being created in the atmosphere by the action of cosmic rays. The number of 14C atoms in a sample of the atmosphere is a constant fraction (about 1.3 x 10-12) of the total number of carbon atoms. Living organisms have the same ratio of 14C to 12C since they continually exchange carbon dioxide (CO2) with their surroundings. When the organism dies it no longer exchanges CO2 with the atmosphere and so the radioactivity of its 14C slowly decreases. By measuring the 14C activity of organic materials found in archaeological sites and knowing the 14C half-life, the age of the material can be determined. The half-life of a radioactive isotope is the time it takes for the radioactivity rate to drop to half its original value.


ISS - The International Space Station


In 1984 the President of the United States, Ronald Reagan, committed the U.S. to developing a permanently occupied space station. NASA invited other countries to join in the project. In little more than a year after Reagan's declaration, nine of the ESA's 13 member countries had signed up, as had Canada and Japan.


More than 900 researchers from those and other countries are developing experiments that will be carried out on the ISS in biotechnology, combustion science, fluid physics, materials science, life sciences, engineering and technology, and Earth science.




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