Tuesday, 1 March 2011

SS-M1: Eppur si muove (and yet it moves)

Today we know that Earth is spherical and that it spins on its axis, and that the Sun is stationary and we orbit the Sun. The Heliocentric model echoes this belief that Earth and other planets revolve the Sun which is near  the centre of the solar system. We are the third planet on this astronomical model.


Many people like Galileo Galilee and Giordano Bruno were persecuted by the Church because they fought for what we all believe today regarding the heliocentric model. However, a few centuries ago many people believed that God’s Earth was at the centre of the universe, and that all other objects orbit around it. This was called the Geocentric model.
Heliocentrism is naturally opposed to geocentrism,   The Roman Catholic Church chose to adopt the geocentric model because it did not conflict with Biblical stories that God revolved everything around us.
Biblical references Psalm 93:1, 96:10, and 1 Chronicles 16:30 include text stating that "the world is firmly established, it cannot be moved" [1]. In the same manner, Psalm 104:5 says, "the Lord set the earth on its foundations; it can never be moved" [2]. Further, Ecclesiastes 1:5 states that "And the sun rises and sets and returns to its place" [3] etc.
Thus, the Church then chose to condemn anyone who spoke or wrote about heliocentrism “unless they spoke of it as a mathematical theory only” [4].
But the transition between these two theories met much resistance, not only from the Catholic Church and its reluctance to accept a theory not placing God's creation at the centre of the universe, but also from the sceptics’ who still needed more evidence.
Many such sceptics’ have argued that the Earth is flat because if the Earth were spherical people would fall off, surely?  [5] 

But we know the Earth isn’t flat. Countless ships and planes have circumnavigated the globe and haven’t ever fallen off the map or seen the edge of the planet!
Another such question is why don’t we feel the earth rotating? [6]
Put simply because we never feel motion.  We only feel changes in motion. For example, when we read or sleep in a fast travelling vehicle, as long as the vehicle doesn't speed up, slow down, turn, or hit a rough spot we wont notice the change. It makes no difference whether you're moving fast or slow, horizontally or vertically. 
You feel nothing until either the speed or the direction changes.
Our Earth, is moving approximately 1,040 miles an hour at the equator,  You don't feel the speed in the direction east along the ground, because it never changes.
If you go outside on a clear night, you can observe the stars rise in the East and set in the West. Why is this?
This is because the Earth moves on its axis which means the Earth is spinning; one side of the Earth would be facing the sun (day time) and the other the moon (night time)
What would happen if the Earth didn’t rotate on its axis?
You could get a situation where there's no rotation. In this case, a day would take an entire year, and it would only happen because of the Earth's orbit around the Sun - Earth wouldn't actually be turning in space but still going around the sun.  In this case, Earth would always show the same face to the Sun - half the planet would be frozen, and the other half would be hot.
Fortunately, the Earth does rotate, giving us a day and night every 24 hours. If the Earth didn't rotate, there would be no day or night. As the Earth turns on its axis, each part of the planet gets a chance to face the Sun and be warmed in a relatively short period of time.
But it can still be argued that it isn’t Earth that is moving it may well be the Sun - so what if the Sun went around the Earth?
If Earth were not revolving around the Sun,  that would mean the same stars would rise and set at the same times, every night. But astronomers have agreed the “stars will be found positioned 1 degree further clockwise” [7] each night compared to the same time the previous night, and this cycle appears to make a full cycle every 365 days, this implies that we are revolving around the Sun once per 365 days.

If the Sun rotated around us, then it would be the same height in the sky year-round since it would have a more fixed path. But it's not. It gets higher in the sky in summer and lower in fall.
I posed a “Philosophical question” on my Facebook account asking if there is proof that Earth doesn’t spin on axis or doesn’t orbit the Sun. 


One sceptic on my Facebook  friend list had offered me “proof” that we don’t indeed move at all.  Comment by Mr. K. :
“if your hovering in a helicopter.
your airspeed indicator is at 0.
your altitude indicator should be level.
your horizontal situation indicator should be steady.
your vertical speed indicator is at 0.

now hover for a couple of hours, the same land is still under you.
should it not be different land, since the ground beneath the helicopter
is rotating on its axis?”


My retaliation to the above statement would be that we all are affected by gravity, Earth is trapped by the sun's gravity. That's why we orbit the Sun. Since the Sun is moving and we are trapped by the Sun's gravity, we are anchored to it. So were also rotating with the Earth. However, if you take that helicopter in to space and hover for a while you will see the land beneath is different and moving.

Bibliography
ARTICLES
Campos, thais, “Philosophers Condemned by the Inquisition” ,(2010), paragraphs 1 / 2/ http://www.suite101.com/content/philosophers-condemned-by-the-inquisition-a209126  [accessed 26/02/2011]
BOOKS
[accessed 27/02/2011]

WEBSITES
J. Richman and C. Pellis ,(2010),Geocentric and Heliocentric Theories. Available from: http://
Gingerich, O.,(2007), “Galileo sun -centred system”. Available from: http://
Psalm 93:1
Psalm 96:10
Psalm 104:5
1 Chronicles 16:30
Ecclesiastes 1:5
[accessed 26/2/2011]

“Christianity and mathematical sciences” accessible from http://www-groups.dcs.st-and.ac.uk/~history/HistTopics/Heliocentric.html
[accessed 27/02/2011]

IMAGES
[accessed 28/02/2011]
http://amazing-space.stsci.edu/resources/explorations/groundup/lesson/basics/g37/


[5] http://answers.yahoo.com/question/index;_ylt=AhhDU0JyJtbRVfZV8_IWliUjzKIX;_ylv=3?qid=20080422091107AAdoUJm
[6] http://answers.yahoo.com/question/index;_ylt=AhhDU0JyJtbRVfZV8_IWliUjzKIX;_ylv=3?qid=20081123130629AAeoZge

Monday, 28 February 2011

SS-H1: James Bradley, Astronomer Royal in the 18th Century





James Bradley (March 1693 – 13 July 1762) was an English astronomer and served as Astronomer Royal from 1742. He was born at Sherborne, near Cheltenham in Gloucestershire. He went to Balliol College, Oxford and took degrees of BA and MA. His early observations were made at the rectory of Wanstead in Essex. Bradley was elected a fellow of the Royal Society in 1718. In 1722 Bradley measured the diameter of Venus with a large aerial telescope with an objective focal length of 212 ft (65 m). James Bradley retired because of a bad health, went to the Cotswold village of Chalford in Gloucestershire, where he died in 1762.

What were Bradley’s major contributions to astronomy?

One of the most significant discoveries of James Bradley was the aberration of light (1725-1728). It is a phenomenon in which a star or other celestial body, as viewed from the earth, appears to be slightly displaced from its true position. It occurs because the Earth is constantly moving in its orbit around the Sun and light travels through space at a finite speed (about 186,000 miles per second [300,000 km/s]). If the Earth was stationary, or if light traveled through space instantaneously, the aberration phenomenon would not exist. For example, the traces left by raindrops on the side windows of a moving automobile provide an analogy to the aberration of light. Even if the rain is coming straight down, the traces will be at an angle.

When observed from the Earth, light from the Sun or any other astronomical object shows an aberration. For the Sun, it is known that light takes about 8.3 minutes to come to the Earth. While the light is traveling, the Earth is revolving around the Sun, and so the Sun appears to move through an angle of about 20 arc seconds. Therefore, the light is actually showing where the Sun was 8.3 minutes ago. We will see the Sun in its true present position about 8.3 minutes into the future (which is how long it takes for the light to reach our eyes).


Another important discovery was the nutation of the Earth’s axis (1728-1748). It is a small cyclical motion superimposed upon the steady 26,000-year precession of the Earth's axis of rotation. It is mainly caused by the gravitational effect of the 18.6-year rotation period of the Moon's orbit. Nutation can be calculated to within arc seconds over periods of many decades. There is another disturbance of the Earth's rotation called polar motion that can be estimated only a few months ahead, because it is influenced by rapidly and unpredictably varying things such as ocean currents, wind systems, and motions in the Earth's core.

In the case of Earth, the principal sources of tidal force are the Sun and Moon, which continuously change location relative to each other and thus cause nutation in Earth's axis. The largest component of Earth's nutation has a period of 18.6 years, the same as that of the precession of the Moon's orbital nodes.

How did these link in with previous work?

Bradley's discovery of the aberration of light was made while attempting to detect stellar parallax (which is an apparent displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines). The discovery of the aberration of light is sometimes told with the story of how James Bradley realized that such thing could exist: once he was in a sailing-boat on the River Thames. He noticed that when the boat turned about, a little flag at the top of the mast changed its direction, even though the wind had not changed; the only thing that had changed was the direction and speed of the boat. He worked out the consequences of supposing that the direction and speed of the earth in its orbit, combined with a consistent speed of light from the star, might cause changes of stellar position that he observed. He found that this fitted the observations well, and also gave an estimate for the speed of light, and showed that the stellar parallax, if any existed, with extremes in June and December, was far too small to measure at the precision available to Bradley. The smallness of any parallax, compared with expectations, also showed that the stars must be many times more distant from the Earth than anybody had previously believed. This discovery was great evidence that the Earth moves and it was announced in 1729.

I have not found information on the roots of nutation of the Earth’s axis, the only thing was that it was discovered by James Bradley and explained only after 20 years from the discovery.

So to sum everything up, James Bradley was a great astronomer and we would not have been able to continue works in astronomy without his help.

References:

Monday, 21 February 2011

AA-U2: Anti-matter

What is anti-matter?


To understand what anti-matter is, we must first look at what matter is. Matter is anything that has a mass, it contains atoms which themselves are made up of protons, neutrons and electrons. The centre of an atom, known as the nucleus contains positively charged protons and neutrally charged neutrons, these are held together by particles known as mesons. The electrons in the atom are negatively charged and orbit the nucleus.
Antimatter in the other hand is the opposite of matter; it consists of positrons (positively charge electrons) antiprotons and antineutrons. Both particles and antiparticles have the same mass but consist opposite charges.

Who predicted it and why should there be such a thing?


The existence of antimatter was predicted by Paul Dirac who was an English physicist (1902-1984) and was described to be the best British theorist after Sir Isaac Newton. The research he did was rather more ‘predicted’ as it was not based on scientific evidence but his methods were based on theory. Dirac constructed a theory by combining quantum mechanics (which described the subatomic world) and Einstein’s theory of special relativity (which states than nothing can exceed the speed of light). The theory and equation he made described how objects that are both miniscule and fast like electrons behave. He found out that his equation works not only for electrons that are negatively charged, but also for electrons that were positively charged, out of this he predicted the existence of antiparticles. Dirac then suggested that there may be an entire other universe consisting of antiparticles where all particles have an opposite charge to the particles in this universe.

How was it discovered?


Anti-matter was already thought to have existed thanks to the work of Paul Dirac; unfortunately it wasn’t discovered until another 6 years later after Dirac proposed his theory. Another scientist named Carl Anderson (as seen on the right) managed to gather evidence from a photograph which proved the existence of antimatter. This came about due to another scientist known as Victor Hess discovering cosmic rays. Anderson designed and built his own cloud chamber (a device used to identify particles) which he used to examine the cosmic rays. He noticed that there were positive and negative particles. What was most intriguing was that the mass of the positive particles was less than that of protons. In order to prove that these were not merely negatively charged electrons moving in a different direction he decided to insert a lead plate into the chamber and take a photograph of it. In the photograph an electron can be seen hitting the plate from the bottom. After it hits the plate it looses energy yet still carries on in the direction that a positively charged electron (positron) would go, thus the discovery of antimatter.

What happens to anti-matter in the world of “matter”?


It is believed that when matter and antimatter collide, they are both annihilated as they cancel each other out and an enormous amount of energy is created. It makes sense that when the big bang occurred, large volumes of matter and antimatter collided producing the huge ‘bang’ but it is not clear why there is an excess of matter left in the universe as it would make more sense to believe that they exist in equal amounts.


Bibliography
http://www.aps.org/programs/outreach/history/historicsites/anderson.cfm  (Carl Anderson figure also taken from this webpage) 16/02/2011

AA-VN: Nuclear Power: Good or Bad?

The controversial energy source Nuclear power has been widely debated through the media and environmentally friendly protest groups. Nuclear power comes through the atomic nuclei, it is extracted through nuclear reactions within the speacalised field of nuclear technology. Currently the only method of acquiring nuclear power is through nuclear fission however other areas are being explored by scientists such as radioactive decay.

The nuclear power is used to generate heat and nuclear energy, which is then transformed to generate nuclear electricity which is regarded as the main advantages of nuclear power. Nuclear power plants are most commonly found in electric generators and nuclear submarines.

Starting with the benefits the most relevant one in todays society is the advantage of nuclear power and its minimal affect on polluting the atmosphere. It does not emiss any carbon, sulfur or nitrogen dioxide and is seen as the cleanest way to produce energy. This is highly preferred to the toxic burning or fossil fuel which is one of the main causes of todays pollution.

In comparison to the waste of fossil fuel, nuclear waste which occurs through the production process of nuclear power is extremely small and confined so does not cause any affect to its surroundings. Scientific studies have shown that a family of 5 could use nuclear power for a lifetime for all their daily needs and the waste produced would be smaller than a golf ball.

The nuclear waste produced upon generation of power is desposed of by taking it to a geological site where it is left to decay, this is done over a period of time and as it has no affect on its surroundings it has no affect on the eco system. Chemical waste such mercury and arsenic do not compose and poisonous gases cause acid rain and more concerninly gobal warming.

There have been two very serious accidents with nucleur power, in Pennsylvania and Chernobyl. This is minimal in comparison to the accidents which are reguary reported in the fossil fuel industries and coal mines which are known to collape and erupt.
The source of nuclear power is uranium and this is available in the crust of the Earth with major sites being uncovered in Canada and Australia. As the source of nuclear power is continuously available now and also for centuries to come, this form of power is literally inexhaustable.

Taking a look at the negative side of nuclear energy, it seems to be a main concern and how it could affect a persons health is still not really know.

The main concern associated with nuclear power is the fear of radiation and this can only be overcome by educating the people about radiation and its side affects. People would be surprised to know that radiation has been a part of our environment ever since its existence and that radiation in moderate amounts can even be advantageous to our health. Radiation does not need to be a negative and can be channeled conveniently to serve mankind and the universe in a positive way.

One of the fundamental problems of nuclear power is the hazard posed by the radioactive materials it produces some of which can be used in nuclear weapons and all of which can be used in so-called dirty bombs. Just one particle of plutonium can be fatal.

Nuclear waste is taken from wherever it is produced, across the country, to Sellafield in Cumbria for reprocessing. During reprocessing, plutonium is separated from other wastes for supposed re-use in nuclear reactors. In reality none of this plutonium is reused for electricity generation. The UK now has a stockpile of over a hundred tonnes of deadly plutonium - and no real idea what to do with it.

The UK now has enough radioactive waste to fill the Royal Albert Hall five times over. There’s still no safe way to deal with it. The government plans to bury it deep underground - out of sight and out of mind. But no one can guarantee that this highly radioactive waste won't leak back into the environment, contaminating water supplies and the food chain.

Aside from the potential risk of a terrorist attact directly onto a nuclear power station, the nuclear industry transports thousands of tonnes of radioactive waste around the UK by road, rail and sea. Every week, communities up and down the country are put at risk from potential radioactive contamination as these trains steam through cities, towns and villages. There are no police or security on board and there are no local saftey measures in place to deal with an emergency. If a nuclear waste train was involved in a terrorist attack, thousands of people could be exposed to cancer causing radiation .

It has been Over twenty years since the world’s worst nuclear disaster, Chernobyl. the human and environmental consequences are still being suffered internationally. Nuclear power is seen as extremely dangerous despite claims of improvements in safety. Scientists agree that another catastrophe on the scale of Chernobyl could still happen at any time.
In conclusion, as with most thing in life-nuclear power comes with the 'good and the bad'.

Friday, 18 February 2011

AA-C1: Ancient Chinese Ideas on Elements

The Classical Elements
In the times where mankind was only just starting to realise and begin to understand the world around them, people began to pull together ideas of the simple elements that are the building blocks of anything and everything.  The classical elements that we know of are Air, Fire, Water and Earth.  But these varied from each country and each religion. In the Western culture it was believed that there were 5 elements, with the fifth element named ‘Aether’, which in some religions was known to be the space in the universe further from our terrestrial sphere, it is believed to be where the Gods live and breathe, of pure essence, as seen from its translation ‘pure, fresh air’ or ‘clear sky’.  This idea was from Greek Mythology but has also been the beliefs of other philosophies such as Hinduism and Buddhism. The four stated of matter were considered as exactly that, all matter, while the 5th element was considered as non-matter, material beyond the world.
The Chinese ‘Elements’
          While the Western culture believed that the elements were simply different kinds of material that formed the basics of life, although many cultures shared this opinion, the Chinese belief had a small but very significant difference.  They believed that these basics were not simply elements but very active forces or different types of energy that were constantly interacting and affecting each other.  We can see this by the translation of our word ‘elements’ which is ‘Wu Xing’ which means ‘the five changes’ or ‘changing states of being’ due to the difference in meaning, Sinologists (the study of Chinese culture) cannot agree on one translation.  By stating that each ‘element’ is a force portrays the idea that our world is very delicate and connected, that each action that happens in this world has a reaction, this is supported in many Chinese traditions, religions and rituals. These five movements were slightly different to that of the Western culture, they included; Wood  ,Fire  , Earth  , Metal  and Water  and they were associated with the early advances of medicine, astrology, martial arts and even military strategy.  It is also thought that they were the original foundation of which we now know as the cardinal points.  All this proving that these states were of great importance and influence in ancient China.
The Cycles
Out of these elements, two cycles were constructed, which were believed to explain the process and change of anything and everything. In the outer ring which explains the generating interaction they are as follows;
  • Wood feeds fire;
  • Fire creates earth (ash);
  • Earth bears metal;
  • Metal collects water;
  • Water nourishes wood.
And in the inner ring, the overcoming interactions
  • Wood parts earth;
  • Earth absorbs water;
  • Water quenches fire;
  • Fire melts metal;
  • Metal chops wood.
The Five Elements and the Five Planets
Each element in the cycle represents many things, for example Metal is associated with autumn, old age, the colour white, the white tiger and the planet Venus.  It is believed that the connection between the five elements and the planets are of most importance as the initial idea that there are five elements was derived from the fact  that even in ancient times, five planets were recognized.  This is astonishing still to believe that without all out latest technology mankind was able to see and distinguish the five closest planets. The Wood Planet (Jupiter); the Fire Planet (Mars); the Earth Planet (Saturn); the Metal Planet (Venus); and the Water Planet (Mercury).  
Although there is still the great debate and the clash of religion and beliefs of what our world and what the world beyond consists of, it is fascinating to realise the vast knowledge and firm grip on truth people had so long ago, and how even today it plays a huge influence on not just science but everything and anything we do.

References

SS-FN: The Flat Earth

What we know to be as a round, relatively small object suspended in an infinitely massive Universe was once a mystery deliberated over by the greatest minds that the world has ever seen. For Centuries and Millennia, theories have changed, evolved and adapted to fit best what humanity could observe and deduce. With advancements in science and technology, more accurate, more plausible and sometimes revolutionary and controversial discoveries were made about the home to all mankind.
Though possibly previously acknowledged and cited in ancient Hebrew texts, our first evidence of Man’s theory of a solar model comes from Anaximander (611 – 545 BC), a man who can be credited as one of the ancient Greek’s earliest great minds. His model depicted earth as the centre of everything, a flat cylindrical world with a projected Y axis, like a short stack of coins. Anaximander also stated that there were three continents; Europe, Libya and Asia. Immediately overhead this was clouds, beyond that (interestingly) was stars before the inclusion of the moon and then the sun. Stars were thought to be small and insignificant with no connection to our sun, something that humanity found to be a star many centuries of years later. The final idea Anaximander contributed was the inclusion of a ‘Region of Fire’ beyond all other objects visible to man. This was the furthest thing from Earth and was said to be an eternal fire beyond which nothing else existed.
                          Anaximander’s model.
Leucippus (450 BC), another Greek philosopher, took Anaximander’s century old theory and subtly altered it. At first glance, the models composed by both men seem similar; this is because Leucippus changed only the ordering of the solar bodies surrounding Earth (which was now shown to be a half sphere with man on the flat surface). In terms distance from the earth, Leucippus was correct. The moon came first in the earths orbit, then planets, then the sun followed by stars. 
                                    Leucippus’s model
From Dante and the Early Astronomers;
M. A. Orr (Mrs. John Evershed), 1913.)

From the previous model, Aristotle (384 – 322 BC) took ideas and the main structure of the cosmos and further altered the ever evolving model. This would be what was accepted by the Greeks and persisted for 1800 years. In what may be seen by a modern man as a backwards step, Aristotle placed the sun between Venus and Mars (only a slight alteration is needed to make this an incomplete modern model of our solar system; swapping the earth and its moon with the sun). In this model, five non-earth planets are accounted for, from Mercury through Saturn. Beyond this were stars and another addition to the solar model, The Sphere of The Prime Mover.  Aristotle included this beyond the stars as a way of including the Gods into a model of the cosmos.
                                               Aristotle’s Model

This, however, this was not the most groundbreaking theory. Aristotle took an idea first considered but never pursued by Pythagoras, that the world was spherical. He had several reasons for concluding this fact. His primary evidence was based neither on philosophy or science but rather religion. He though that if God were to create and object he would make it entirely symmetrical and perfectly formed as a sphere.[1] This evidence was backed up by other observations, such as the curved shadow on the moon when lunar eclipses occurred and ‘Every portion of the Earth tends toward the center until by compression and convergence they form a sphere.’(de Caelo 297a9-21). Furthermore, Aristotle’s theory of a round earth explained the way in which constellations moved up or down when tracking the latitude of the Earth. Aristotle’s reputation preceded him, and his word was gospel truth, thus explaining the endurance of his theory.

SS-ON: Lunar Eclipses

Lunar eclipses have always been a topic of interest throughout history and many civilisations have strived to try and find out how and why lunar eclipses occur as well as the frequency in which they occur. This is because of how mysterious and beautiful a lunar eclipse looks, especially in past civilisations. A lunar eclipse is said to occur when the moon passes behind the earth and because of this the sun’s rays do not reach the moon because of it being blocked by the earth. This can only happen when the Sun, Moon, and the Earth are aligned together or very close together.

 
This diagram clearly shows the formation of lunar eclipses and how they occur. The umbra is the darkest part of the earth’s shadow while the penumbra is the lighter part of the earth’s shadow. This confirms that for a lunar eclipse to occur the planets must be aligned and that depending on the position of the moon a certain eclipse will happen. There are multiple types of lunar eclipses which are shown in the table below:

First Contact
Beginning of the Penumbral Eclipse
Second Contact
Beginning of the Partial Eclipse
Third Contact
Beginning of the Total Eclipse
Fourth Contact
End of the Total Eclipse
Fifth Contact
End of the Partial Eclipse
Sixth Contact
End of the Penumbral Eclipse


As can be seen there are 3 types of eclipses. The penumbral eclipse happens when the moon enters the earth’s penumbra. The partial eclipse happens when only part of the moon has entered the earth’s umbra. The total eclipse happens when the moon has travelled completely into the earth’s umbra.

This picture above shows how the colour of moon changes as it enters the different stages of the eclipse(Penumbral to Partial to Total and back again) and also how a total eclipse only occurs when a full moon is present.
Every year there are atleast 2 lunar eclipses with a maximum of 5 possible per year, however a total lunar eclipse doesnt happen very often. If you know the time a lunar eclipse will happen then you can use a Saros Cycle to predict when the next eclipse will happen.
The Saros Cycle is an eclipse cycle that states that when an eclipse occurs another almost identical eclipse will occur after 18 years and 11.3 days. This cycle can then be used to create  a saros series which is multiple eclipses that have been predicted by the saros cycle and eventually this saros series will end as the eclipse differs greatly from the last,  a new saros series will then begin.
So far it has been shown what our civilisation currently knows about lunar eclipses is great compared to past civilisations however they were still able to make correct predictions and findings. One of the first civilisations to manage to calculate when an eclipse would occur were the Chaldeans (1200 BC) using the Saros Cycle.
Eclipses back then were often seen as evil omens by the Greek’s who would make predictions about what would happen in the world based on the eclipse. Making predictions based on eclipses made sense to them as they didn’t have as much information about the world as we have so they had to make educated guesses about it. The Greek’s also managed to explain why an eclipse happens. Thales (620 – 546 BC) realised that the stars, moon and   the sun were all solids. He also found that the moon was lit by the sun which explains why a lunar eclipse happens because of the earth blocking the sun’s light from reaching the moon. The Greek’s also were able to predict when a lunar eclipse would occur just as the Chaldeans had done using the Saros Cycle however they called it something different.
To conclude lunar eclipses are beautiful and have always been a large topic of interest. A lunar eclipse occurs when the Sun, Earth and the Moon are aligned together while the earth blocks the Sun’s light from reaching the moon. There are 3 types of lunar eclipses which are called Penumbral eclipses, Partial eclipses and Total eclipses. Each have different conditions for them to happen and a total eclipse can only take place when the full moon is present. Also there are around 2-5 eclipses every year but total eclipses occur very rarely. A lunar eclipse can be predicted using the Saros Cycle early civilisations such as the Greek’s used the Saros Cycle to predict the time of eclipses and also were able to explain why lunar eclipses happen which is a great feat.
References