February 18, 2014

Space and Time

The constituents of the universe: space, time, matter and energy

Author: Subir Kumar Bhattacharyya

While I am defining that space, time, matter and energy are the ultimate and basic ingredients of the universe, scientists will not stop at that and add another element, that is, the laws of physics, elegantly explained and formulated in mathematics. The entire domain of science that encompasses the whole gamut of our life- where we live, that is, the entire universe, why we live and what is life all emerges from the four basic constituents as theorized above like hundreds or thousands or more of descendants emerge from a single parent. The scientists have gone further to theorize that everything was created and evolved and is still evolving from a single element, that is, energy. Laypersons are sure to scoff at this proposal, because of age-old belief based on our senses, particularly from the influences of religions, lack of scientific education and usual aversion to new ideas. Even poets, litterateurs and eminent artists practising fine art and performing arts may question how these crude elements could bequeath nature so many colours, varieties, so much charm, grandeur and captivating beauties and humans such divine virtues and sublime traits and such bonds of love, parental affection, adoration and loyalty as make this planet earth an enchanting abode that none is willing to part with.        The scope of any essay for publication in a newspaper is limited, but the expanse, depth and dimension of the subject is so colossal and all encompassing that the entire scientific knowledge comes under its purview. I shall attempt at explaining why my suggestion makes sense, but at the same time confess that I may not be able to do justice fully to the article in this format. In future, I shall revert to this subject from time to time to satisfy curious readers.

The laws of physics are expressed in terms of mathematics because the latter is the lingua franca of the universe. Most of the mathematical formulae are inaccessible to laypersons and as such it is always challenging to explain all these phenomena in simple language. The concept of space, time and spacetime combined is still evolving as there are three/ four competing concepts. I shall dwell on these later and begin with matter and energy, the concepts of which are resolved and discernible, but theories are still evolving in search of unification and elegance. Everything we see in nature however pretty, majestic and tender is divisible and can be separated into molecules and further split into atoms of any or more in combination of 92 elements occurring in nature. There are some man-made elements. The difference between living beings, both floral and faunal species including humans (Homo sapiens) and non-living objects is that the former is made of organic molecules while the latter made of inorganic molecules. Organic molecules are basically carbon compounds. Colours are properties of substances to absorb and emit one or more colours of light-spectra. The light-spectrum, which consists of seven visible light colours (acronym VIBGYOR) and invisible light waves such as ultra-violet, x-ray and gamma-ray on the left side of the spectrum (more energetic light waves) in that order and infrared, microwave and radiowave on the right (much less energetic), is in fact various frequencies of light waves perceived by our brain through inputs from eyes as different colours to differentiate among various frequencies. Colour perception varies from species to species. As such they are not fundamental property or reality of nature, but its perception is the creation of our brain to optimize the chances of our survival. The diversity that we see in nature is the variation in molecular structure formed by the atoms of ninety-two elements in different combinations. Most of the atom is just empty space. The rest of the atom consists of a positively charged nucleus of protons and neutrons (neutral or no charge) that are surrounded by a cloud (existing like waves) of negatively charged electrons. Protons and neutrons are not fundamental constituents of matter/ atom, they are made of quarks. The nucleus is the center of the atom. An atom is an extremely small particle of matter that retains its identity during chemical reactions.

Avogadro's number and the mole are very important concept for the understanding of atomic structure. Avogadro's number is 6.02 x 1023, and the atomic mass number (no of protons and neutrons) in grams is the mass/ weight of 1 mole of that element. One mole of an element or a compound contains 6.02 x 1023 atoms or molecules. For example, one mole of magnesium atoms or 6.02 x 1023 magnesium atoms weigh (12 protons plus a little heavier 12 neutrons in the nucleus of one atom) 24.3 grams. A mole of carbon or 6.02 x 1023 carbon atoms weigh a total of 12.0 (6 protons plus 6 neutrons) grams. An example may be given to show how small an atom is. If an apple were magnified to the size of the earth, the atoms in the apple would be approximately the size of the original apple. Atoms can only be observed individually using special instruments such as the scanning tunneling microscope. Over 99.94% of an atom's mass is concentrated in the nucleus with protons and neutrons having roughly the equal mass, neutron being slightly heavier. A molecule of any matter is much heavier than individual atom constituting the molecule. As for example, a mole of sand, spread over the United States, would produce a layer 3 inches deep while one mole of oxygen weighs 16 grams and that of silicon weighs 28 grams.

The size of the nucleus is much smaller than that of the whole atom. The radius of a nucleus is approximately equal to (1.07)3√A fm, where A is the total number of nucleons or the total number of protons and neutrons. The radius of an atom is in the range of 105 fm. 1 fm or femtometer is equal to 10 to the power minus 15 (10-15) meters. In comparison, the ratio of the radius of helium atom vis-à-vis that of its nucleus is 40,000:1. If we consider the shape of both the atom and its nucleus to be spherical, the volume of the atom (volume= 4/3pi times r3) is 64x1012 times that of the nucleus. This explains how infinitesimal the volume of the mass (ignoring the mass of electrons) is compared to the volume of the empty space inside the atom. Then how is it that we feel solidity of matter? It is because of interplay of various forces inside atoms, between atoms, inside molecules and between molecules constituting matter. Many mechanical, electrical, magnetic, optical and chemical properties of solids are the direct consequence of Pauli's exclusion principle, meaning that no two fermions (an electron is a fermion) can occupy the same quantum state. Energy can be defined as the ability of a system/ body/ force to exert pulls or pushes against the basic forces of nature, along a path of a certain length. The total energy contained in an object is identified with its mass, and energy like mass cannot be created from nothing or destroyed. According to Einstein's famous equation E = MC2 (it is considered the most famous equation in science), mass can be converted to energy and energy to mass, provided there is enough energy. 1 kg of mass has the energy equivalent of 9 x 1016 Joules and as such 1 gram has the energy equivalent of 9 x 1013 Joules. However, only a fraction of mass can be converted to energy. Nuclear reactors employ fission process to generate energy (electricity is a form of energy). Fusion process that keeps stellar including solar energy output alive converts hydrogen (hydrogen used as fuel) into helium, and a fraction of mass is converted to energy. Fusion process releases much more energy than fission process does. However, controlled fusion so far remains beyond the reach of human ingenuity. 

Human qualities and virtues did not become the standard traits of human character at once, they evolve over time. We must remember only such qualities became our defining characteristics as enhanced the chances of our survival. All human qualities including defining characteristics of emotion like love, compassion, filial affection, loyalty, adoration and negative attributes like hate, revenge and cruelty and so on are encoded in our genes contained in the DNA inside our cell nucleus and passed down to succeeding generations. These emotion and traits are the result of interactions and sharing of neurons in the brain. In fact, all traits that we possess individually are the result of interplay among genes, environment at home and outside, upbringing and some luck, meaning that some favourable factors what we call luck. Human behaviour, propensity and the like are now greatly understood because of advancement in neuroscience. Further elaboration is beyond the scope of this article and I wish to stop here.

While explaining how human characteristics have evolved over time, I wish to put down a few lines on consciousness, the perception or impression of being before I dwell on matter and energy. Although neuroscience is developing, neuroscientists have discerned how brain creates emotions and are unanimous presently in their opinion that we, the humans, have no free will, validating the long-held belief among the scientific community that the free will or the strong feeling that we are in charge is in fact an illusion. Elaborating further, our brain always maintains a 3-dimensional picture of our surroundings; constantly updating the mental picture drawn from inputs received from sensory organs and makes us act in consonance with that picture. The brain takes inputs from senses by electrical impulses and processes them in various constituent parts of the brain and transmits decisions (outputs) or reactions that various organs of our body need to act on in response to the environmental stimuli. The time lag between reception of inputs to and transmission of outputs or instructions from the brain to executing organs ranges from 3/4th of a second (opinions about lower range vary from half a second to as long as 1 second) to several seconds. But the brain has to take instantaneous decisions in response to stimuli. Because of the compulsions under which the brain functions, it is only logical that it reacts according to mental picture, not in direct response to environmental stimuli. At the conscious level, the brain occasionally takes corrective measures (they could be hazardous occasionally) deviating from mental pictures in case it finds that the pre-conceived response is not adequate for survival. 

Now reverting to matter and energy, I explain some fundamental laws of physics and draw the subject to a wholesome conclusion. According to the ‘Standard Model' of particle physics, there are four fundamental forces of nature- electromagnetic force (light, electricity and magnetism combined), weak nuclear interactions or force, strong nuclear force and gravitational force and several dozens matter particles and number of assumptions. They interact with one another according to the laws of physics and produce everything what we see in nature. An example will explain how the number of fundamental particles has grown over time. In an atomic structure, electrons revolve round a nucleus consisting of protons and neutrons, protons being positively charged and neutrons neutral. All protons should have been scattered and not confined within the nucleus because like charges repel each other. Scientists first theoretically deduced and then experimentally verified that masons hold them together. It was further discovered that protons and neutrons are made of quarks, and these fundamental particles cannot exist in isolation, they must combine to form proton and neutron and their electric charge is a fraction and not an integer. Scientists then found out why quarks always paired up because strong nuclear force holds them together (the force particle is gluon). In this way, scientists proceeded to discover new fundamental particle to account for specific behaviours. The existence of all these fundamental particles was verified experimentally in laboratories. Quantum mechanics explains the behaviours of particles and cosmic phenomena at the micro level and theory of relativity explains at the macro level, that is, behaviours of large-scale structures like stars and galaxies. Both these theories hold good in their respective fields but they are not compatible meaning that when they are combined to account for black holes and so on, absurd results come out. Grand Unification Theory (GUT) was postulated to unify three forces in nature except gravity. As the models described above are inelegant, scientists all over the world are fully engaged in finding a single mathematical formula or theory that explains every object and every phenomena occurring in the universe. Evolving superstring theory and M- theory are developments in that direction. 

Space and time are the two most enigmatic elements in the universe. What we perceive with our senses as space and time is fundamentally wrong and our perception is just an illusion. Mathematicians and physicists aided by mathematics discern their properties and what they mean and how they behave. The basic attributes of space and time are that space is curved or/ and indented owing to the presence of massive bodies and time of moving bodies flows slower than that of bodies at rest.

In explaining the attributes of space, I must warn the readers at the outset that space is not like anything we think space is. We generally think of space as a complete vacuum or zero vacuum entity endlessly stretching in all directions. The informed readers are aware that waves of electromagnetic force, that is, photons are all-pervading and they are constantly moving at the velocity c until they are absorbed by some matters enhancing their energy. If we imagine that completely empty space is spread all over to infinity, light rays radiating from stars would have been fully sucked by that empty space beyond the boundary of our universe and never return. But observations by scientists confirm that light rays are being reflected. These findings lead to the realization that our universe must be cut off from the empty space, if there is anything like that. We mistakenly think of space as a stage on which all particles and massive bodies like stars and galaxies are going about their individual journey or are dancing to the tune of an invisible creator like actors perform on a stage their respective roles according to a script and under instructions of a director. Images of deep space received through satellite-based observatories confirm that the space we see or visualize has many properties unlike our mental picture. I wish to deliberate on the subject from philosophical point of view. Either God created the empty space or infinite space naturally exists for eternity. Why should God create empty space infinitely stretched in all directions whereas an infinitesimally small space (compared to infinite space) is used to accommodate this universe? Why should God create this universe in this particular place, not in other place? Why should empty space exist stretched to infinity in all directions whereas a very small fragment is necessary for this universe? Moreover, nature abhors redundancy. Even if we think there is infinite space outside our universe, it has no connection with our universe and our universe is completely cut off making it a self-contained and bounded one.  

 Some of the counterintuitive properties of space are described below.

1)      Space is expanding. It does not mean celestial bodies like stars and galaxies are moving away from us or from one another. If it means that celestial bodies are moving away from us, the velocity of recession would have been the same for all heavenly bodies irrespective of their distance from us. Contrary to popular belief and imagination, the more distant a celestial body such as a star or a galaxy is from us, the faster is its velocity of recession. Direct observations prove beyond doubt that space is expanding meaning that every point or every cubic centimeter of space is expanding. As a result, cumulative effect of the expansion of space at every point propels all celestial bodies from us and away from one another at recession velocities directly proportional to the distance from us and away from one another.

2)      Space is not continuous. Space is discreet or grainy in constituency. Scientists therefore use the term ‘fabric of space' to denote graininess.

3) Space is always seething with activities. Empty space is not empty. It has energy and as a result, particles and anti-particles are constantly forming and are immediately annihilated releasing energy.

4)      The fabric of space is distorted due to movement of particles. In fact, space interacts actively with matter and energy and is warped or curved and indented in presence of or to accommodate massive bodies like the sun. This is one of the findings of Einstein's theory of relativity. Bending of light rays traveling near the sun was first demonstrated in an experiment conducted by British scientist Arthur Stanley Eddington sometime in the 1940s. Curvature of space is a reality that a pilot flying an airplane can only ignore at his own peril.

5)      Space is not absolute. It is squeezed, dented like a well, curved due to the presence of massive bodies, and curved path or arc formed joining two points, which is part of the great circle, is the shortest distance between the two points, not the straight line. As space, all bodies, all matter and force particles are in a state of flux, there is no fixed frame of reference. Inside matter, molecules and atoms are constantly changing position and as such what we see as solid bodies at rest in fact move, albeit very slowly not visible through our naked eyes and decay over time.

Curvature of space is such a fundamental property of the universe that it needs elucidation so as to make readers understand its features. A few questions are naturally logical and relevant and needs be addressed. What does curvature of space mean? What are its attributes? How is it going to affect our understanding of the universe? Curvature of space is really a curved space. The mental picture about space that we have is that of a flat space. If we roll a piece of A4 size paper either length-wise or breadth-wise, the boundaries of both sides come closer and closer until they meet, making the shape of the piece of paper a cylinder. Latest observations confirm that the curvature actually leads to a complete bending round and closing up of space so that it becomes a domain of finite extent. For the purpose of our discussion, the closed space may be generally taken to be spherical. In a spherical space, if one goes on in the same direction, he will eventually come to the starting-point again. As there is no boundary, no point can be used to leave or enter a closed space. All these features constitute a self-contained finite universe. Perhaps the most fundamental characteristic of a spherical universe is that at great distances from us or any point, there is not so much room as we could have imagined. Let us take the example of the earth's surface. The surface area within two miles of say, GPO, Dhaka is nearly 4 (2x2) times the area within one mile. The surface area within 6,000 miles is considerably much less than 6000x6000 times the area within 1 mile. This could be easily visualized. Similarly, in 3-D curved space of the universe, the volume of space or amount of room within two light years (distance) of the sun is nearly 8 times the volume or amount of room within one light year. However, the volume or amount of room within 2 million light years is significantly less than 8 times of the volume within 1 million light years. The more distance we consider, the volume of space or amount of room will gradually diminish and the amount of diminution is inversely proportional to the distance.

In this context, I wish to refer to Stephen Hawking, who succinctly drew analogy of 2-D curved surface like the surface of earth to define the features of 3-D curved space. We know from observation what the characteristics of 2-D curved surface are. i) The curved surface is bounded and there is no edge or boundary and none can fall off the surface. ii) There is no vantage point or place that can claim that it is only at the centre. In fact, every place will find it is surrounded by equal number of places on all sides. iii) The centre of the 2-D curved surface is located nowhere on the curved surface, but somewhere on the third dimension. Similarly, the curved space of the universe is bounded; there is no edge or boundary and none can leave or enter the curved space. There is no special place; every star or galaxy is surrounded by equal number of stars or galaxies on all sides, and no star/ galaxy can claim any special position. The centre of the 3-D curved space will locate nowhere on the 3-D space, but somewhere on the fourth dimension. I have already explained how volume of space or amount of room diminishes in direct proportion to the distance from any point or star/ galaxy, and it holds good for every star/ galaxy.

As I am discussing time and its properties, the readers are advised to first accept the idea that time, like space is weird and counterintuitive. Like space, time is not absolute, it is variable. There are, however, some constants of nature. The most fundamental constant of nature is the velocity of light c, which is always constant, irrespective of the velocity of an observer or the source of light. As the velocity of light is constant and space is variable, time is also variable. Different observers in relative motion will keep different times. A simple calculation is laid down for more curious readers. Velocity of light c equals to distance light traverses divided by time a light ray takes. Distance is variable because of distortion, lengthening or squeezing of space and as such time can't be constant because in that case c will be variable, contradicting bed-rock principles of physics. Time slows down for an observer in motion relative to an observer at rest. Time-related equation in Einstein's special relativity very well establishes the relation how time elapses for different observers in relative motion.

Theoretical physicists have perhaps spent more time to demystify time than they have done to address other subjects. Julian Barber, a renowned physicist demonstrated in his book "The end of time' that passage of time is an illusion. The finding can simply result from the definitions of space and time and the equation of velocity, that is, v = dx/dt. What the equation is saying is that, if an object moves over any distance dx, there is an elapsed time dt. Since time is defined in physics as a parameter for denoting change (evolution), the equation for velocity along the time axis (not along space axis) must be given by v = dt/dt which is self-referential. The self-reference comes from the simple differential calculus that says dt/dt (differentiation of t with respect to t) always equals 1. To emphasize, it is logically impossible for the t coordinate of an object to change because such a change is self-referential. That means there is no time travel, no motion in spacetime. 



Article Source: http://www.articlesbase.com/science-articles/the-constituents-of-the-universe-space-time-matter-and-energy-6004604.html

About the Author

The author has a Master of Science degree in mathematics and is a former Ambassador. He was associated with a large healthcare institution, a public-private joint venture in Bangladesh, as an adviser, which is spread all over Bangladesh and is second to the government in healthcare delivery. He authored a book entitled 'Africa- Through the Eyes of a Diplomat'. He regularly contributes stories, science articles and political developments to English dailies in Bangladesh.


All about Comets

Author: Michael Newman

Comets can be spectacular objects seen in the night-time sky. They have been associated by the superstitious with disasters and other notable historical events. Until the 1986 opposition of Halley's comet, the true nature of a comet's nucleus was the subject of argument amongst astronomers. The passage of the Giotto probe close to the nucleus of Comet Halley and the many observations that were carried out worldwide have vastly improved our knowledge of the nature of comets.

Because comets can be seen so easily, records of the observation of comets can be traced back over many centuries. It was from a study of the historical observations of several comets that Halley, using Newton's new theory of gravitation, showed that the orbits of several comets around the Sun were almost identical. He postulated that they were all the same object and predicted that it would be seen again at a certain time in the future. As we know, Halley's comet did reappear around the predicted date and has been seen since then on each of its journeys in towards the Sun.

Comets, as seen from the Earth, appear to have some sort of nucleus which is surrounded by a bright, more or less circular region called the ‘coma' from which one or more tails may be seen spreading out away from the direction to the Sun. These tails when photographed can be seen to be different colours. There is often a filamentary structured tail which is bluish and a series of more amorphous tails which are yellowish. The supposed nucleus of the comet is the bright centre of the coma. The coma and the tails develop markedly as the comet gets closer to the Sun with tail lengths sometimes growing as long as 100 million kilometres.

The Orbits of Comets

The first computation of cometary orbits was made by Halley, as mentioned above. Since then the orbits of many hundreds of comets have been determined. They almost all fall into two types; periodic orbits, which take the form of very eccentric ellipses, and parabolic orbits.

The orbits of many comets have periods ranging from hundreds of years to tens of millions of years, indicating that they spend much of the time far outside the orbits of Neptune and Pluto. The orbits of the long-period comets are not confined to a plane, like the orbits of the planets, and these comets can appear in any part of the sky. In order to explain the orbits of comets, astronomers have postulated the existence of two groups of comets on the edges of the solar system:

The Oort Cloud:

In 1950, Dutch Astronomer Jan Oort proposed that a large, spherical cloud of comets surrounds the solar system. The Oort Cloud is supposed to be almost 1 light year in radius and could contain up to a trillion small, icy comets. Small perturbations to the very slow motions of these bodies will cause one of them to start its long, slow journey towards the inner solar system under the gravitational pull of the Sun. The orbit of such a body will be a parabola with the Sun as its focus. As the comet gets closer to the Sun its velocity increases reaching a maximum at its closest point whereupon is starts its journey back out to the outer reaches of the solar system, never to be seen again. The Oort Cloud has never been observed, only theorised, but its existence would explain the orbits of long period comets, which have orbital periods greater than 200 years.

Sometimes, during its journey through the solar system, a comet may pass close to one of the major planets. If this encounter is a close one then the gravitational pull of the planet will dramatically change the comet's orbit and can alter the parabolic orbit into a closed, elliptical orbit. The comet the becomes a periodic comet with a definite period for its returns close to the Sun. Halley's comet is the best known example of such a comet. The existence of periodic comets, with orbital periods less than 200 years, led to the proposal of a second source of comets:

The Kuiper Belt:

The Oort Cloud does not explain the existence of comets which have orbital periods of 200 years or less. In 1951, astronomer Gerald Kuiper suggested that another belt of comets existed beyond the orbit of Neptune, between 30 and 50 astronomical units (4.5 to 7.5 thousand million km) from the Sun. In 1988, a group of astronomers at the University of Hawaii and the University of California at Berkeley began searching for Kuiper Belt objects using a 2.2m telescope in Hawaii. They discovered the first Kuiper Belt object in 1992. Subsequent observations from Hawaii and with the Hubble Space Telescope have discovered dozens of icy objects, each a few hundred km in size and with orbital periods of a few hundred years. The Kuiper Belt may be composed of comets from the Oort Cloud, which have been deflected into smaller orbits by Jupiter or the other outer planets.

A few comets have very short period orbits. For example, Comet Encke has a period of 3.5 years, the shortest known, which places its orbit inside the orbit of Jupiter. It is generally thought that these inner solar system comets originated in the Oort Cloud or the Kuiper Belt but passed close enough to one of the giant planets to be deflected by its gravitational pull into a much smaller orbit.

The Cometary Nucleus

Until the Giotto probe showed us pictures of the nucleus of comet Halley there was considerable discussion of the nature of a comet's nucleus. We now know that the nucleus is small, about 10-20 kilometres across, is irregular in shape (rather like a peanut), and is almost black. From it jets of gas and dust are forced out by the Sun's radiation. We believe that under the black skin there is a solid body composed of ices of various kinds, including water-ice, dry-ice (made of carbon dioxide), ammonia, methane and many other organic carbon compound ices all mixed together with dust. The dust contains silicates, carbon and carbon compounds.

The Cometary Coma

Surrounding the nucleus is the bright coma. This is composed of gas and dust which has been expelled as the Sun evaporates the icy nucleus. The parent molecules are mainly split up by energetic ultraviolet radiation from the Sun into simple compounds. These are not necessarily like stable chemicals that we know on the Earth but are simple combinations of atoms. For example, some of the most numerous are CN, C2, OH, C3, H2O+ and NH2. These are broken down pieces of larger chemicals, such as water (H2O) and organic carbon compounds. The expelled gas and dust form a roughly spherical ball around the nucleus. This is many times larger than the nucleus - the coma of a bright comet can be millions of kilometres in size, whereas the nucleus is only 10km or so across. The coma of the Great Comet of 1811 was larger than the Sun.

The action of the Sun's radiation and the magnetic field associated with the solar wind remove gas and dust from the coma and it is ‘blown' away to form the comet's tail.

The Tails of a Comet

The gas which is blown away from the coma is ionised by solar radiation and becomes electrically charged. It is then affected strongly by the magnetic fields associated with the solar wind (a stream of charged particles expelled by the Sun). The gas tail is made visible by line-emission from the excitation of the gas by the Sun's radiation. This gives the gas tail its characteristic blue colour. The geometric shape of the tail is governed by the magnetic structures in the solar wind but predominantly the gas tail points directly away from the direction from the comet to the Sun.

The dust is blown away from the coma by radiation pressure from the sunlight absorbed by individual dust grains. It moves in a direction which is governed by the motion of the comet, by the size of the dust particles and by the speed of ejection from the coma. The dust tail can be complex, multiple and even curved but, in general, will point away from the Sun. Sometimes, due to projection effects, part of the dust tail can be seen pointing in a sunward direction. This is just due to the fact that the comet and the Earth are moving and that part of the tail has been ‘left behind' in such a place as to appear to point towards the Sun. The dust tail is yellow because it reflects the Sun's light to us.

The gas tail can be about 100 million km long while the dust tail is around 10 million km long. The longest observed tail on record is the Great Comet of 1843, which had a tail that was 250 million km long (greater than the distance from the Sun to Mars!).

The Names of Comets

A comet takes the name of its discoverer, or discoverers. It also has a serial number consisting of the year and a letter designation. In this way all comets are named uniquely. Halley's comet is one of very few exceptions to the naming rule. Halley did not discover ‘his' comet but has the honour of having his name attached to it because of his pioneering work in determining the orbits of comets and showing that this comet was periodic.

Prediction of Comets

Apart from the periodic comets, whose orbital periods are well known and hence whose returns can be predicted with great accuracy, it is impossible to predict when comets may be seen in the sky. Most of the brightest and most spectacular comets have been ones which have appeared only once and have never been seen again. When a comet is discovered, far from the Sun, it is very difficult to predict how bright it will appear when it comes close to the Earth and the Sun. Some comets seem to emit a lot of gas and dust and produce long and spectacular tails whereas others only produce a small amount of gas and dust and have almost no tail at all.


Orbital Period

Perihelion Date

Perihelion Distance


76.1 yrs.


0.587 AU


3.30 yrs.


0.340 AU


6.51 yrs.


1.346 AU

Tempel 1

5.51 yrs.


1.500 AU


6.86 yrs.


1.358 AU


6.52 yrs.


0.996 AU


5.09 yrs.


0.989 AU


27.89 yrs.


0.743 AU


5.29 yrs.


0.528 AU


5.46 yrs.


1.063 AU


32.92 yrs.


0.982 AU

Schwassmann-Wachmann 3

5.36 yrs.


0.937 AU


6.24 yrs.


1.571 AU


6.46 yrs.


1.596 AU

Wild 2

6.39 yrs.


1.583 AU


50.7 yrs.


8.460 AU


4.29 yrs.


1.000 AU


4000 yrs.


0.914 AU


~40000 yrs.


0.230 AU

See More Articles on this Topic HERE

Article Source: http://www.articlesbase.com/science-articles/all-about-comets-1293566.html

About the Author

Michael Newman - Tutor,Writer,Economist: http://homework-expert.net

Saturn - Titan

Saturn's moon may hide vast oceans and water means possibility of life

Author: Stig Kristoffersen
DYPT OG VÅTT: Observasjoner utført av NASA-sonden Cassini antyder at månen Titan - Saturns største - kan ha et enormt og dypt hav skjult under et skall av is. Foto: AP Photo/NASA, JPL, Space Science Institute/SCANPIX

Observations by NASA's Cassini spacecraft suggest that Titan - Saturn's largest moon can have huge and deep oceans hidden under a shell of ice.
Photo: AP Photo / NASA, JPL, Space Science Institute / SCANPIX

Saturn's moon may hide vast oceans

And where there is liquid water there is life.

PLASK: Titan er den eneste kloden utenom Jorda hvor det er påvist innsjøer på overflaten, her i form av flytende metan. Også her spekuleres det i om liv kan ha oppstått. Dette bildet av overflaten ble tatt av Huygens-sonden som dalte ned til månen i 2005. Foto: NASA/SCANPIX

Titan is the only planet other than Earth where lakes are found on the surface, in the form of liquid methane. Here, too, speculation of whether life might have arisen. This image of the surface was taken by the Huygens probe that descended to the moon in 2005.

IS OG VANN: Forskerne tror det kan være over 400 km dypt hav skjult under overflatelaget bestående av opptil 200 km is. Grafikk: NASA/JPL

The researchers think it might be over 400 km deep ocean hidden beneath the surface layer consisting of up to 200 km ice.
Graphic: NASA / JPL

Saturn's moon Titan may hide a vast ocean of liquid water, according to observations by NASA's Cassini spacecraft. And where there is water, there may be life - at least as we know it.

Cassini has investigated the Saturn ring system and moons since 2004, and observed that some details of Titan's orbit and rotation does not match that it is composed of solid through and through, according to Space.com .

The observations and anomalies may make sense if the Titan - the largest of Saturn's moons over 60 - have oceans under the surface, probably composed of liquid water, "says Cassini scientists in a new study in the journal Astronomy & Astrophysics .

- We believe that the occurrence of an ocean is likely, "said the head of the study, planetary scientist Rose-Marie Balanda at the Royal Observatory in Brussels, Belgium.

Deep Ocean

The study joins the ranks of many who concluded that the moon, which is slightly larger than our own, can not be a completely solid body, but hide an ocean beneath a "shell" of ice. Balanda said the team used these studies as a starting point.

- We found the idea very interesting, and decided to take it a little further, "she told Space.com.

The figures are difficult to estimate accurately, but the study suggests that the outer layer of ice may be 150 to 200 km thick, while the possible ocean beneath is between 5 and 425 km deep. On the basis of ideas about how the moon was formed, scientists believe that the sea are mostly water, with a possible "dash" of ammonia, Balanda said.

Titan will not be unique about this match. Also, Saturn's moon Enceladus and Jupiter's Europa - one of the hottest candidates for possible life elsewhere in the solar system - probably deep ocean beneath an icy surface.

Lakes of methane

Titan is the only planet other than Earth where lakes are found on the surface, then in the form of liquid methane, and scientists have long thought that might be the source of life.

For while it is speculated that life could arise during the quirky and unexpected circumstances, the chemistry and relationships - as in methane lakes - have scientists who hunt organisms elsewhere in the solar system also based on the only life we ​​so far know: That here on earth. Here on earth access to water - H 2 O - is of crucial importance for life to exist.
Astro biologists still do not know what are the necessary conditions for life to arise, but it seems that the presence of liquid water is required, "says Balanda.

Not yet proven

Several observations and more research is needed before it can definitely conclude that Titan hides a big ocean. Current and rotation characteristics can possibly be explained by that the moon has been recently disturbed, such as comet or asteroid impact.

- Our analysis strengthens the possibility that Titan has an ocean beneath the surface, but it proves it beyond doubt. So there is still a job to do, "Balanda to Astro Biology Magazine .

Article Source: http://www.articlesbase.com/nature-articles/saturns-moon-may-hide-vast-oceans-and-water-means-possibility-of-life-4747969.html

About the Author

Stig-Arne Kristoffersen has a background as civil engineer and geoscientist. He has worked mainly within the oil and gas industry from the mid 1980s. He has written a few fictional novels as well as being the author of some professional litterature within oil and gas sector, he act as a writer to various web sites.

February 03, 2014

Astronomy News - Sky Chart

Astronomy News: What's Happening In The World Of Astronomy?

Author: Gary Nielson

When there are billions of stars in the galaxy, there are a billion and one reasons for an amateur astronomer to stay up at night to watch the sky. If you've been bitten by the stargazing bug, give in. It's a very enjoyable hobby. To help you get started, here are some things you might want to know:

Get A Sky Chart

A sky chart or a field guide can help you find where the stars are in the heavens. Since their positions change depending on the seasons, you can use the sky chart to help you find a particular star immediately. You can also map out the locations of different constellations and recognize any star in the night sky by simply referring to your sky chart.

Those more tecnologically miden might prefer to use astronomy software either on a laptop or a mobile phone to simulate the night sky so identifying celestial objects is easier.

What To Look For

The star that shines brightest in the northern hemisphere is Sirius. You might also want to find Polaris, the North Star. If you're a little lost, you can look to the Big Dipper (Ursa Major) to show you the way. Find the 'bowl' or 'ladle' of the Dipper. The two stars located away from the handle are the Pointer Stars, called Dubhe and Merak. Follow where they point straight towards the North and you will find Polaris.

Don't forget to enjoy the Little Dipper (Ursa Minor), Cassiopeia, Draco, Cepheus and other constellations – there are 88 of them (about half in the Southern hemisphere), some of which are visible at different times of the year.

You can also watch for falling stars or meteor showers. Their appearance is usually announced on TV and in newspapers. On special nights, you can enjoy hundreds of meteors streaking across the night sky.

Star Light, Star Bright

Stars are categorized by brightness, which is measured by magnitude. The magnitude scale has the brightest stars having 0 or even negative magnitudes. For example, Sirius has a magnitude of -1.46. Vega, a star that shines bright during summer, has a magnitude 0. Polaris has a magnitude 2 and Antares has a magnitude 1. Stars with a magnitude of 29 need the Hubble Space telescope to be seen and get this: they are 250,000,000,000 times less bright than Vega.


As a newbie astronomer, you don't really need a telescope to enjoy stargazing. It's best to familiarize yourself first with stars and constellations using just your naked eye at first. You can also use a good pair of astronomy binoculars since these will do the job nicely. Buy a telescope only if you're already familiar with the night sky and enjoy it to the fullest.

Final Thoughts

One of the major benefits of learning astronomy is the ability to observe rather than just look. The moon is one heavenly body that everyone is used to seeing. To the observant astronomer, the moon actually passes through a cycle of phases that lasts for twenty eight days.

When you begin to notice the subtle differences in the position and phases of the moon, it is evident that you are now in tune with the moon's distinct rhythm.

The planets also travel across the sky during the year and change position from year to year as the amount of time they take to orbit the Sun is different to the Earth.

Probably the most elusive objects are the comets. Asteroids are discovered pretty regularly, but they tend to have well defined and predictable orbits. This is also the case with some comets but many others are on a one-time visit to the inner solar system, and will be flung out into interstellar space as they pass close to the Sun. There's only a short amount of time to see these objects before they're gone forever.

Article Source: http://www.articlesbase.com/education-articles/astronomy-news-whats-happening-in-the-world-of-astronomy-4898701.html

About the Author

Learn more about astronomy. Stop by Gary's site where you can find all the latest astronomy news. Astronomy News: What's Happening In The World Of Astronomy?

February 01, 2014

Dark Matter

What is Dark Matter

Author: Omkar

Introduction on what is dark matter:

Dark Matter and Dark Energy are hypothetical concepts hypothesized in the late 1990's to explain accelerating expansion of universe. Prior to the discoveries made possible by Hubble Space Telescope (HST) it was believed that expansion of universe has to stop at some point of time due to force of gravity. It followed that there should be at least some signs of slowing down.

HST made it possible to observe very distant supernovae with a startling discovery that the universe is actually accelerating its pace of expansion. There was no explanation for the observed phenomenon even though there had to be a cause.

Explanation of what is dark matter

Attempts to explain this discovery of accelerating expansion of universe led theorists to come up with conjectures. One possibility was that long-discarded version of Einstein's theory of gravity and its hypothesis of a "cosmological constant" may be correct. Second possibility was that there could be some strange kind of energy-fluid that filled space with the last possibility being that Einstein's theory of gravity may need to be revised to include some kind of field overcoming gravity and causing this observed cosmic acceleration.

The correct explanation is still unknown but the possible solution has been named as dark energy. Existence of dark energy in large quantity can be safely assumed due to its effect on expansion of the universe. But beyond that it is an absolute mystery. It is estimated to constitute about 70% of the Universe with its twin dark matter constituting about 25%. Everything else observable by instruments known to us is estimated to constitute less than 5% of the universe. May be dark energy and dark matter are the normal phenomena of space as what we consider normal and observable is a very small component of the whole.

Conclusion on what is dark matter:

It is easier told what dark matter is not than defining what it is. Theoretical models for the composition of the Universe designed to match actual observations have led scientists to estimate the ratios of dark energy, dark matter and normal matter (70:25:5) given above.

We are certain that dark matter is not in the form of observable stars and planets. It is also not in the form of dark interstellar clouds of matter and it is not antimatter either. It is also not in the form of large black holes because these can be estimated by the number of observed gravitational lenses and there are simply not enough such lenses to make up 25% of dark matter.

There do remain a few viable hypothetical possibilities. One of these is baryonic matter made up of the dark matter all tied up in brown dwarfs or possibly in small, dense chunks of heavy elements. These have been hypothesized as massive compact halo objects. But the generally accepted view point is that dark matter actually made up of some other kind of particles like Axions or Weakly Interacting Massive Particles (WIMPS).

Article Source: http://www.articlesbase.com/k-12-education-articles/what-is-dark-matter-6605044.html

About the Author

Comprehend more on about Projectile Motion is Caused by and its Circumstances. Between, if you have problem on these topics Speed Practice Problems Please share your views here by commenting.