The sun is a main sequence star classified as a type G2 V yellow dwarf, it has more mass and temperature than a normal star but is considerably smaller than a blue giant. The lifetime of a star type G2 of the main sequence is about 10 billion years. The age of the sun is estimated at 5 billion years. The sun follows an orbit around the galaxy at a distance of 25,000 to 28,000 light-years from its center, completing one round in approximately 226 million years. Around the sun are the orbits of all eight planets (earth is the third planet from the sun) with its satellites, as well as other bodies such as asteroids and comets, all bodies within the solar system.
The shape of the sun, after elaborate measurements have shown that it is almost perfectly spherical, with an average diameter of 1.392.000 km. (109 times of that of earth) with a widening of about 9 millionths, which is mainly due to the gravity of Jupiter.
In view of the size of the sun often talked of is the “apparent diameter of the sun.” Apparent diameter of the sun is the angle of the ABC from which it is observed that the sun from the earth when A and B have fundamental difference points of the circumference of the disc of the sun and C point of the earth (observer). The bisector of angle ABC is the distance earth to sun. The apparent diameter of the sun changes during the year. On January 3 takes the largest value equal to 32′ and 36″,2 on July 4 is limited to the minimum value of 31′ 32″. Therefore, the average apparent diameter is 32′ 4″1.
This change in apparent diameter proves that earth does not move around the sun in a circular orbit but in an elliptic way so that on 1 January the distance of earth-sun receives the minimum value of 147.100.000km, and on July 2 the maximum value of 152.100.000 km, so the average value of distance is 149.504.312 km.
Luminance measurements of the sun showed that it is 12 x 1010 times brighter than a star a’ sized and 23 x 107 times brighter of light of all the stars put together. For this reason, during the day it hides them. Finally in relation to to the full moon is 56 x 104 times brighter than that. The sun seems so bright just because of the relatively small distance from the earth, always compared to other stars. If, however, was only 10 parsec it would appear as a dim star, around 5th magnitude. More precisely the absolute size of the sun is 4.8. When observing the sun with a telescope does not appear uniformly bright throughout the disc, but brighter in the center and dimmer at the periphery of the disc (as in the adjacent image, the indicative list). This indicates that the solar sphere is surrounded by the atmosphere that absorbs the light.
Full sphericity of the sun can be explained by the slow rotation. From the visual and spectroscopic examination reveals that the solar sphere rotates on its axis from west to east, and the time needed for rotation, on average reaches 25 days and 23 minutes. But time is not stable at all points of the surface. Thus in the region of the solar equator is limited to 24 days and 15 hours while at distance of 45 ° from the equator it reaches approximately 28.5 days, while at the poles it is observed is even greater.
The core is found in the solar center and has a diameter of approximately 175,000 kilometers (0.25 solar radius). It is estimated that in the area of the center the density of solar material is 70 times more of liquid water while the pressure reaches 2 X 1011 atmospheres (atm). Under such conditions and with a temperature of 14 x 106 degrees, the atom of elements are in an ionized state and so compressed, so the material of the solar core as gas can be more consistent and solid. It is natural that the radiation of the inner layers of the core causes pressure on the overlying layers.
Just above the solar core, layer thickness is 400 kilometers (km) and which reaches up to the surface. This layer of the solar sphere from which all the radiant solar energy comes from, i.e. heat and light are called photosphere. Therefore the whenever we observe the disc of the sun it corresponds to photosphere.
Above the photosphere, solar material is verified that exists, and especially in a layer with large thickness. This is called the solar atmosphere or helium atmosphere. The atmosphere of the sun is not visible, because its temperature and moreover the brightness is less than the photosphere, so as to hide it from the intense diffusion in the daylight, just as the stars are hidden. They become visible with the total eclipses of the sun as a bright halo that surround the disc of the sun.
The solar atmosphere is divided into two separate layers. The first of them situated directly above the photosphere is called chromosphere. Its height reaches about 15,000 km, and its temperature reaches up to 100.000 ° C. It has a strong pink color, hence received the name chromosphere. Above the chromosphere lies the corona or solar corona, or corona of the sun of which boundaries reach a distance of five solar radius. The temperature of the corona is about 1.5 × 10 sixth degrees.
The sun consists of 74% hydrogen, 25% of helium and 1% from other elements. Hydrogen constitutes the main fuel for the thermonuclear reactions that produce energy which radiates, while the helium comes mainly from the products of nuclear fusion of hydrogen.
The sun does not have a clear surface like the other planets. The gas density decreases according to the rays of the sun with an inverse square law. The sun’s radius is measured from the center of the star until the photosphere, out of which no fusion takes place.
Albert Einstein E=mc2.
The sun is a huge sphere of various gas whose sovereign is hydrogen and helium. The temperature of the sun is so great so even the metals are vaporized. The amount of energy which it produces is incredible. It has been determined that every second the sun radiates as much energy as would an explosion 4 billion of hydrogen bombs with 100 Mt (megaton) each. And all this for a single second, while the sun radiates for almost 5 billion years and will continue to do so for as many.
As mentioned above, every second about 655 million tons of hydrogen from the mass of the sun are converted into 650 million tons of helium which continue to consist a mass of the sun. From this difference 4.6 million tons are transformed into energy. The material of which is the heart of the stars is composed of a mixture of free cores and free electron. Because hydrogen is the main component of the stars, this means that the stellar plasma consists mainly of free protons which have to be united to form the helium element. Under these circumstances, the sun is a huge thermonuclear reagent that converts hydrogen into helium. Especially during this process in every second converts into energy 4,6 million tons from its mass. Besides the fact that it loses so much mass, it is so huge and for billions of years to come will lose one one-hundredth of its mass. All the stars in the sky radiate energy in the same manner even if they are smaller or larger and warmer.
The general background of the internal structure of the stars is due to the english Physics Astronomer Arthur Eddington (1882-1944) and long before the energy source of the stars was discovered. Eddington had described the situation in the heart of stars as follows: “within a cubic centimeter (cc) are concentrated a trillion trillion atoms, approximately double free electrons and 20 billion trillion x-rays. X-rays move with the speed of light and electrons at a speed of 16,000 km per second.
This procedure was firstly explained, however, by the german-american Physics Hans A. Bete in 1938 where he was awarded the Nobel Prize in Physics in 1967.
There are two main types of thermonuclear reactions which occur in the mass of stars. One is called the proton-proton chain and the other carbon cycle. In both of these types of reactions 4 hydrogen nuclear (H-1) merges into one helium nucleus (He-4) radiating simultaneously a total of energy of 26.2 million electron volt. During this procedure when 1000 grams of hydrogen merge they create 993 g of helium (He), which means that a total of just 7 grams is lost. And it is this that becomes so much energy.
The mass of the sun are not such as to lead to a situation of nova or supernova . However it is estimated that in 4 to 5 billion years, the depletion of stocks and the transmutation of hydrogen into helium and later into heavier elements, will begin to expand and form a red giant. This will happen because the pressure from the fusion of heavier elements is greater than that of hydrogen, in order to balance the weight will increase the volume of the sun. Although it is likely that the extent of the red giant contains the earth’s orbit, recent studies support that the process of expansion of the red giant will promote the earth into a remote orbit, preventing its sublimation. After the phase of the red giant, the sun will become a white dwarf, which is surrounded by a planetary nebula, and will cool for the next 5 billion years. Another theory based on the searches that have been made in the recent years supports that in 5 billion years the sun, because of its huge mass, will compress so much in order to create a black hole and consequently all the planets in the solar system, including earth, may be lost.
The sun in astrology is the ruler of Leo.
Eclipse in astronomy is the phenomenon in which earth enters the shadow of a celestial body, with the result that the self-luminous body that creates the shadow to lose a part of its brightness or it cannot be observed fully or partially from earth.
Lunar Eclipse: a natural phenomenon in which the moon stops receiving the sunlight as between these two celestial bodies, earth passes between. Eclipse of the Moon can be observed during the night and when the moon is a full moon.
Solar Eclipse: a natural phenomenon in which the moon passes between the sun and the earth, resulting in some regions of the earth to receive less light than usual. Eclipse can be observed during the day and when the moon is new moon.
The moon and the earth belong to celestial bodies with reflection of light like all planets and their natural satellites. The light that we can see from the moon at night comes from the reflection of light on the surface of the sun. Depending on the location of the earth, sun and moon phases of the moon are generated (new moon, first or last quarter, full moon). For a lunar eclipse to occur it should be found in the shadow of the earth. This can only happen when the sun, earth and moon are on the same straight line, or approximately on the same straight line and the earth is between the two celestial bodies. Something similar for a solar eclipse to occur it should be found in the shadow of the moon. This can happen only when the sun, earth and moon are on the same straight line, or approximately on the same straight line and when the moon is between the two celestial bodies.
If the level of the moon’s orbit around the earth was the same to the level of the earth’s orbit around the sun (level of the ecliptic), then we would have a lunar eclipse and a solar eclipse every month, i.e. every time that the moon is in a full moon phase and new moon respectively, so as every month the three celestial bodies would be aligned. But these two layers form between them an angle of about 5ο 8’ and both orbits intersect the celestial sphere in two points called ascending node and descending node. The straight line which joins the two nodes is called the line of nodes. To align the three celestial bodies the sun and moon should be near these nodes. When the sun and moon are simultaneously both close to the same node then we have a solar eclipse, when the two celestial bodies are in different nodes then lunar eclipse occurs.
During a year the sun passes once by each node, as a result creating two eclipse seasons, i.e. two periods of time of which eclipses can occur.
Because of the attraction that the moon receives the line of nodes turns to the west at 20ο which corresponds to approximately 20 days. So there is a chance in one year to belong to three eclipse seasons if the first eclipse season coincides with the beginning of the year. Within a year we can have 2 to 5 solar eclipses and none to 3 lunar eclipses.
The above frequency with which solar and lunar eclipses occur may seem strange as from our daily experience we know that the announcements of the lunar eclipses are more frequent than those of the solar eclipses. This is due to the fact that the solar eclipses occur more often, though, have less duration, as a result they can be observed only by very few and specific areas around the earth. A total eclipse of the sun can last up to 7.5 minutes while the usual time is far less. On the other hand a total eclipse of the moon can last longer than 1,5 hour and for this reason is visible in most parts of the earth.
The phenomenon of the eclipses is periodic and for this reason it is easy to predict the time it will happen. The movement of the line of node performs a complete rotation around 18 years and 11 days. This period is called the period of Saro (Saros) and the method of determination of lunar eclipses is called the Saros cycle.
A total solar eclipse is a rare celestial phenomenon in which the disc of the moon gets tangent internally with the solar disc hiding all traces of the sunlight for a few minutes. This is because, at the celestial sphere, both bodies seem to have exactly the same size. It is a cosmic coincidence, since the sun is 400 times further away than the moon, but it seems so respectively and 400 times smaller.
Because the orbit of the earth around the sun is not circular but elliptic, and in conjunction with the elliptical orbit of the moon around the earth, for the ground observer both bodies continuously change size. This has as a result the creation of three types of eclipses.
The total eclipse, the partial eclipse and the annular eclipse.
During the annular eclipse the cone shadow of the moon does not touch the earth’s surface. As a result, the observer sees a solar ring around the dark body of the moon (purple area).
At the partial eclipse the observer sees a percentage of the Sun “eaten” by the moon (open purple area).
The total solar eclipses can theoretically last up to 7:30 minutes. The annular solar eclipses can theoretically last up to 12:30 minutes
The first recorded solar eclipses’ reference comes from China in 2136 or 2159 BC. Servants Ho and Hi were killed by the emperor because they were unable to forecast the eclipse. In China they believed that a dragon swallowed the sun.
In 1178 BC and specifically on the 16th April refers to Homer’s Odyssey
«…and the sun got lost in the sky and an unholy fog covered everything ‘.
Reference of Archilochus for the total solar eclipse of 6 April 648 BC
“Zeus, the father of Olympian Gods, turned the day into night hiding the sparkling light of the sun, and deep fear conquered the people “.
In 585 BC we have the first probable forecast of the solar eclipse from the Thales the Milisio, as recorded by Herodotus The eclipse became the reason for the cessation of hostilities between the Medea and Lideious.
Countless are the reports of solar eclipses from Greeks, Chinese, Romans and other nations of ancient times. Then, in the ancient times, an eclipse was considered a bad omen. Nowadays it is considered the elite of celestial phenomena. Some people travel to the ends of the world to live the experience of the totality even for a few minutes.
The stages of a total eclipse
A total solar eclipse lasts usually three hours (if the observer is on the path of totality).
At the beginning the moon makes its appearance on the solar disc as ‘ a bite ‘. This is called a first contact and means the beginning of the eclipse.
The phenomenon is progressing without giving to the observer a sign of the dramatic changes that will happen. When the covering over the solar disc from the moon overcomes 70% it begins to be perceived of a slight reduction in the brightness of the surrounding area. At 90% the sunlight has been reduced significantly.
The phenomenon of the diamond ring
Five minutes before the second contact or otherwise the start of totality, the sunlight that reaches earth comes from a very thin package. As a result to be observed the phenomenon of shadow zone (shadow bands). The observer sees on large white surfaces belts of shadows succeeding one another at a high speed.
Another impressive phenomenon, just before totality, is the shadow of the moon which is coming from the west at a frightening speed and begins to plunge into darkness the adjacent areas.
One minute or even less before the total phase, it can be noticed in the last rays of the Sun as they pass through the valleys of the moon, forming something similar to the string of beads and that was firstly observed by Francis Baily in 1836. These are beads of Bailey (Bailey’s beads).
A few seconds before totality, Bailey’s beads begin to fade in a flash of lightning and when the last of them are left, you see the impressive corona of the sun, who together with the last bright beads form the so-called diamond ring. And immediately afterwards the black disc of the moon takes the position of the sun. ..
In a few minutes that follow the sky darkens and the brilliant stars of the sky make their appearance, venus and mercury. In the center of the sky, and at the point where the sun was, now dominates the solar corona which extends even at a distance of 8 solar radius. The phenomenon is unique. The observer can distinguish thin red projections that spring from the surface of the sun like nuclear languages, the so-called solar flare. Around the horizon takes a reddish color, since the diameter of the shadow rarely exceeds 250 km, and beyond this coverage never reaches 100%.
The violent interchange from day to night mixes up the animals, who think that it got dark and go to their nests, birds stop to chirp and flowers close their petals.
The minutes pass and the few-minute night gives its place to the day with the third contact and the end of totality. The above phenomena happens vice versa and gradually the sun appears and as it enlarges, the light comes back gradually.
The average Earth-Moon distance is 384,403 kilometres (it is observed that this distance is increased by about 0.2 cm per month and this is occurs due to the tidal forces). The diameter of the moon is 3,476 kilometers (about 1/4 of the Earth ‘s). The gravity on the surface of the Moon is in tension around the 1/6 of the Earth. It rotates in the slightly inclined axis in 27 days, 7 hours, and 43 minutes, exactly the same duration that lasts for its orbital revolution around the Earth. This coordination is the reason that we see from Earth always the same aspect, something which is due to the gravitational attraction of the Earth. The Earth and the Moon gravitationally are a single body with a common gravitational center. A consequence of the above is that 59% of its surface is visible from earth.
The solar eclipses are caused by the moon when it seemingly passes in front of the Sun, shading a part of earth, opposed to the lunar eclipses which are caused similarly by the planet earth.
Several mechanisms have been proposed for the formation of the Moon 4,527 ± 0,010 billion years ago, some 30-50 million years after the origin of the solar system. These mechanisms include the fission of the Moon from the Earth’s crust by centrifugal forces, which would call for an excessively great initial spin of the Earth, the gravitational capture a pre-formed Moon, which would require an unfeasibly extended atmosphere of the Earth to dissipate the energy of the passing Moon, and the co-formation of the Earth-and moon together in the primordial accretion disc, which does not explain the depletion of metallic iron in the moon. These hypotheses also can not account for the high angular momentum of the Earth-Moon system.
The most probable is the impact of a planet with proto-earth.
After the collision the particles that blasted from the impact into space were raised into orbit around the Earth and in the end formed the Moon.
In 1969, Neil Armstrong and Buzz Aldrin, when sending the Apollo 11 the mission of Apollo, were the first people who stepped on the surface of the moon. Followed by ten other astronauts during the missions Apollo 12, Apollo 14, Apollo 15, Apollo 16 and lastly Apollo 17 in 1972. The return of the man on the Moon is planned around 2020, with NASA’s Orion Program, and there are plans for a manned mission by the Chinese.
On November 13, 2009 NASA announced that the LCROSS mission, with a controlled crash device at the south pole of the moon was able to discover significant amounts of water.
The basic movements of the Moon are two.
Moving around the Earth in an elliptical orbit and completes one rotation around its center in 29,53 days. This period is called a synodic month. It also rotates around its axis and completes one rotation in 27,3 days. This period is called a sidereal month. The result of these two movements are that the Moon always shows the earth its same face. This phenomenon is called the synchronous rotation of the Moon and is due to the equation of time of its rotation around the Earth and its rotation around its axis.
In astrology the Moon is ruler of cancer.
Characteristics of the surface
Seas and Valleys
Ocean of Storms
Phases of the Moon
Waxing crescent moon
First quarter moon
Waxing gibbous moon
Waning gibbous moon
Last quarter moon
Waning crescent moon