What are comets???

Comets are balls of dirty ice from the outer solar system that follow elliptical orbits with high eccentricities, so that they are near to the Sun for only a small portion of their lives. As a comet comes near to the Sun at perihelion, the outer layers heat up and turn to gas, causing a coma (halo) and a tail to form. Very close
to the Sun, the tail of a comet splits into two pieces, an ion or plasma tail and a dust tail. While both tails point away from the Sun, the dust tail curves ‘‘back’’ along the orbit, while the plasma tail is swept straight away from the Sun by the solar wind.

These tails can be as long as 1 AU, making comets the largest objects in the solar system. However, comet tails are extremely diffuse; comet tails are more perfect vacuums than any we can make on Earth. The entire mass of a comet is less than 1 billionth the mass of the Earth.The nucleus of a comet is a few kilometers across, and contains lots of water ice and carbon dioxide ice. This nucleus is surrounded by the coma—this is the‘‘head’’ of the comet. The coma can be over 1 millionkm across. The coma shines both by reflected sunlight, and by the transitions of excited atoms and molecules in the gas.

Parts of a comet

Comets can be divided into two types—long-period and short-period comets. This distinction is not quite as arbitrary as it sounds, since there are two different reservoirs for comets in the solar system.

1. LONG PERIOD COMET
The long-period comets come from the Oort cloud, a swarm of comets 50,000–100,000 AU from the Sun. These comets
have been in the Oort cloud since the solar system formed, and contain material that has remained the same since before the Sun formed. The Oort cloud is approximately spherical in shape, although there is probably a denser region near the plane of the solar system. An ice ball leaves the Oort cloud to become a comet when a star passes nearby (within 3 light years), and changes the ice ball’s orbit. The passage of a star slows the ice ball, so that it no longer has enough energy to maintain its orbit. These objects fall into long elliptical orbits around the Sun. It is rare for such an event to happen; about 10 stars per million years pass close enough to change the orbits in the Oort cloud. Each star may affect several ice balls, however. There are probably trillions of icy balls in the Oort cloud.

2.SHORT PERIOD COMET
Short-period comets have periods less than 200 years, and originate in the Kuiper belt. The Kuiper belt is located just outside the orbit of Neptune, between about 30 and 50 AU from the Sun. These comets are distributed in a flat ring on the ecliptic. Extrapolating from known Kuiper belt objects indicates that there are probably about 70,000 comets in the Kuiper belt larger than 100km across. Each time a comet passes near the Sun, it sheds some of its mass, which remains in the orbital path. Eventually, the comet disintegrates entirely, unless, of course, it runs into the Sun, a planet, or receives a gravitational ‘‘assist’’ out of the solar
system during one of its orbits.

Kuiper Belt

SUPERNOVA

Supernova is the explosion of a star in the galaxy that emits more energy than nova. Supernovae are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy, before fading from view over several weeks or months. In the end of star life,the star will cause supernova. But not all star will have supernova, just star that have more than 8 times mass of sun (=>8Msun). Sun mass is 1.99 x 10³⁰ kg. After supernova,the next step of star evolution is become neutron star(star initial mass<=8Msun) or black hole(star initial mass=>8Msun).

Image of Supernova

Cassiopeia A Supernova

Based on spectral lines in supernovae, we can found several types of supernovae

1.Supernova type I
This type can found on elips galaxy,the old galaxy that have old stars in majority. Supernova I is weaker than supernova type II.Supernova type could divided again as :

a.    Supernova Ia    => there is hydrogen  spectrum line

b.    Supernova Ib/c  => there is no hydrogen or helium spectrum line
2.Supernova type II

When observation, we can found Hidrogen line on this supernova type. Generally,supernova type II happen in young galaxy,like spiral galaxy that contains young stars.

Step of supernova

1.    Swelling

Star swelling because it send his Helium core to the ouside layer. Star will become red giant star as the swelling. It will become brighter (luminosity increase),the color become red, but its temperature will decrease. The mass become heavier than before.

2.    Iron(Fe) core forming

Because the hydrogen as the main energy source from nuclear fussion reaction was run out,iron will be produced on the core.

3.    Explosion

The star’s core temperature increase until 100billion°C. Then this energy will transfered to outside and explode,create shock wave .This explosion will create new elements cause of the material from explosion fused.

Supernovae have implications for life beyond the stars, among them:
Produces Metal
1. At the core of stars, nuclear fusion reaction occurs. In this reaction born elementsheavier than Hydrogen and Helium. When that happens, these elements are thrown outthe stars and enrich the surrounding interstellar cloud with heavy elements.

2. Creating Life in the Universe
Supernova catapult certain elements into space. These elements are then transferred to other parts far from the exploded star. It is assumed that the element or material is thenjoined to form a new star or even a planet in the universe.


Source : http://en.wikipedia.org/wiki/Supernova

Black Hole

What is black hole actually???

Black Hole is a big concentration of mass that make a very large gravity area. Because of it,nothing could escape from it gravitional area. Need speed of light to escape from it. Black hole come from the star evolution's .Actualy the last step of star evolution. Black Hole comes from main sequence stars,but has mass 8 times than the sun.

First,the star will become supernova cause of it explosion (the star).This explosion created as the gravitonal colappse. The star couldn't produce energy from fussion reaction again.The star will become unstable,then the star shrink.After that, the star will explode. Throw out its atmosphere and its materials. The star will become brighter than before. We call this supernova. In the next step of its evolution,if the star mass 25 times than the sun,it will become the black hole,if lower,it will become neutron star.

An illustration of black hole

 HAVE BLACK HOLES BEEN OBSERVED?
Because of its gravity power,nothing could escape,include light can't escape than it. Light just could enter the black hole,but couldn't escape through it So,we couldn't observe the blackhole because it absorb light

HOW COULD WE KNOW THERE IS BLACK HOLE???
In earlier astronomer has predicted that there is a black hole.Albert Enstein is the one from the astronomers.After he found his gravity theory,he predicted it.It still became a controversy a that time. Nowaday,we could prove the black hole through X-ray Telescope.The emission of black hole is X-ray wave.If some place in space that radiate so many X-ray wave,it means there is a black hole in there.

IS THERE ANY BLACK HOLE NEAR THE EARTH???
The answer is no. Why?Because to become a blaca star must have 8times mass of sun. The kind of that star commonly placed near the core of galaxy.And the distance from us is very far. Our solar system placed about 30.000light years from the core.

WHAT IS ON THE CORE OF OUR GALAXY???
A super massive black hole. The astronomer estimated there is a supermassive black hole on the core of our galaxy,in same case for other galaxy.A galaxy could rotate because there is a super massive black hole on the core of galaxy.

SOURCE : http://en.wikipedia.org/wiki/Black_hole

What is Astronomy???

Astronomy is a natural science that deals with the study of celestial objects ( such as stars, planets, comets, nebula, star clusters and galaxies ) and phenomena that originate outside the Earth's atmosphere. Study of astronomy include with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the formation and development of the universe. So,astronomy is a dynamic science and progress forward with the new discovery of the scientists.

Astronomy is one of the oldest sciences. Prehistoric cultures left behind astronomical artifacts such as the Egyptian monuments and Stonehenge, and early civilizations such as the Babylonians,Greeks, Chinese, Indians, and Maya performed methodical observations of the night sky. However, the invention of the telescope was required before astronomy was able to develop into a modern science. Historically, astronomy has included disciplines as diverse as astrometry, celestial navigation, observational astronomy, the making of calendar, and even astrology, but professional astronomy is nowadays often considered to be synonymous with astrophysics.

Nowadays, astronomy divided into 2 big branches, the theory and the observations. The theory based on the idea created by scientists,as example "Big bang Theory" is the one,created by Edwin Hubble, the one of the oustanding astronomer. Through the theory , we could describe the phenomena of astronomy,as example created of universe ,explain by the "Big Bang Theory". Observational astronomy based on the observation of astronomers. The astronomers gather the data and make a summation that created an astronomy law. Of course, making the law using the basic priciples of physics.

Many Astronomical object or law's found by the amateur astronomers .They contributed so many .Their summary or observation's data gathered and created an astronomy's law ,as it written before.

source : http://en.wikipedia.org/wiki/Astronomy