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N - Factary


Naked eye (observation)


See also, magnitude.


An observation made without using any equipment such as binoculars or a telescope. Never use your naked eye to look at the Sun.



The faintest stars which can be seen with the naked eye are approximately of astronomical magnitude 6. The angular resolution of the eye is between 0.5 and 1.0 arcminutes.


Never use your naked eye, binoculars, a camera or telescope to look at the Sun directly.

Always project the Sun's image onto a piece of paper or film.


Nano (n)


A prefix meaning one billionth of something. That's 0.000 000 001 or 10-9 of something.

Nano can be abbreviated to 'n'. For example, nm is the abbreviation for nanometre. This is a useful measurement when discussing things as small as the wavelength of some electromagnetic radiation.


Nanometre (nm)


Usually abbreviated to nm, this is the unit of length most commonly used for describing the wavelength of electromagnetic waves all the way from visible light to gamma rays. It is equal to 10-9 (one billionth) of a metre and to 10 Angstroms.

The wavelength of visible radiation ranges from about 350 nm to 650 nm.



NASA logo


America's space agency: the National Aeronautics and Space Administration. That’s a fact worth remembering for quizzes! The most common misinterpretation of the initials is probably National Astronomy and Space Agency. The European equivalent is ESA (European Space Agency) - pretty much as you would expect!




An elementary particle with no charge and almost no mass, which interacts very weakly with other matter. It was named by physicist Enrico Fermi and means 'little neutral one' in Italian.



Millions (well, actually nearer two hundred trillion trillion trillion!) neutrinos are produced every second by the nuclear reactions in the centre of the Sun. However, since hardly anything can stop them, they escape into space almost straight away, unlike electromagnetic radiation, which can take tens of thousands of years to make its way from the centre of the Sun to its surface.


It has been estimated that billions of these neutrinos pass straight through our bodies every second, but because they really are very hard to 'catch' only one or two will ever collide with the atoms in your body during your whole lifetime.


The so-called 'neutrino problem' has puzzled solar astronomers for many years now. After neutrinos were discovered in 1956 and predictions made as to how many the Sun was producing, it seemed a good idea to build an instrument to try and detect some to check out our understanding of the way they are produced and the way they interact (or don't as the case may be) with other matter.


Unfortunately, when these neutrino detectors were built they were only able to find a fraction of the neutrinos expected. Was there something wrong with the calculations of how many neutrinos the Sun was producing? Did this indicate a fundamental misunderstanding of how fusion energy in the Sun was released? For many years this looked like a possibility, but in 2001 new results from the Sudbury Neutrino Observatory in Canada showed that in fact the Sun does produce the expected number of neutrinos. It was realised that, on their journey to the Earth from the core of the Sun, many of the neutrinos produced would change into a different kind of neutrino. There are three kinds of neutrinos known as the electron, muon and tau. The Sun produces the electron type. When these change to muon and tau forms, they cannot be detected by the instruments on Earth. However, knowing how many of them do change form, it is possible to calculate how many original electron neutrinos are produced and that turns out to be as expected.




An electrically neutral elementary particle with 1839 times the mass of an electron. Neutrons are present in the nucleus of all atoms except hydrogen. When atomic nuclei of the same element contain different numbers of neutrons, they are said to be different isotopes of that element.


The three isotopes of Hydrogen.

Image showing the 3 isotopes of hydrogen


Neutron star


Jocelyn BellThe final stage of a star which has slightly more mass than the Sun. When stars like that come to the end of their lives, production of energy stops and gravity pulls the star tighter and tighter together until all the matter collapses into neutrons. Because they consist of very compact matter, almost pure neutrons, neutron stars are small and very dense. They rotate rapidly and emit beams of radio waves, which, as the star rotates and the beam sweeps across the Earth, are seen as pulsar radio sources. The signals from pulsars were first detected using a radio telescope in Cambridge, England by Jocelyn Bell and Anthony Hewish. At first, because of the signal’s perfect regularity, the astronomers considered the possibility that these signals were artificial and sent by another civilisation.

    Professor Jocelyn Bell

Image of Sir Isaac NewtonNewton, Sir Isaac (1642-1727)


Newton was a true genius, one of the world's greatest scientists. He was born in 1642 into a farming family. He attended Trinity College, Cambridge University, but since he was poor, he had to do menial tasks for the Fellows to pay his way and he wasn't particularly good at his studies! He was liked even less because he was a solitary person who loaned his money to other students to make a profit. Everyone knows Newton to be a great scientist, but not a loan shark!


In 1664, the Great Plague broke out and the University was closed. He went home and began studying the nature of light. His early investigations looked at what happened when light passed through a glass prism. He showed that white light is made up of different colours. He built the first telescope that used mirrors instead of glass lenses.


Newton is well known for his three Laws of Motion and most famously of all for his Law of Gravity. This states that every object in the universe attracts every other object with a force which is proportional to the product of their masses and inversely proportional to the square of the distance between them. In short, everything tries to clump together! The story (probably made up) suggests that a falling apple made Newton wonder whether the force exerted by the Earth, which made the apple fall, was the same force that made the Moon 'fall' towards the Earth and kept it in orbit. Whatever did provide the inspiration, Newton went on to develop his Law of Gravity, which he used to explain the motion of planets around stars and satellites around planets.


newton (N)


The SI unit of force, symbol: N. A force of 1 newton is the force necessary to accelerate a mass of 1 kg by 1 m/s2. Force was defined by Sir Isaac Newton in his Second Law of Motion which says that:


force = mass x acceleration


F = ma

The most common force you probably come across is 'weight' and that is associated with the most common acceleration you come across - that due to gravity. If we put some numbers in the equation above we have that the force (or weight) of a mass of 1 kg being accelerated by gravity at the Earth's surface (about 10 m/s2) is:


weight = 1 kg x 10 m/s2

             = 10 newtons



Notice that the unit we call a newton is just a shorthand to save writing the SI units out in full i.e. ( - that’s ‘metre kilograms per second squared’



Nuclear fusion


The process in which atoms of lighter elements are joined together to form atoms of heavier elements, and during which huge amounts of energy are released. Very high temperatures and pressures are required for this process to work. The most common place where this is known to occur is in the cores of stars such as the Sun which, at a temperature of 15 million °C, provide ideal conditions for the fusion of hydrogen into helium.




The positively charged core of an atom consisting of protons and neutrons around which electrons orbit. The one exception is normal hydrogen, which has just a single proton and no neutrons in its nucleus.


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