Black hole

HI...

the new topic today is about BLACK HOLE (requested by Victor)

and since YAHA asked me to make it in a formal style...

i'll make this post in formal style..

 Black hole is a region of space in which the gravitational field is so powerful that nothing, not even a light can escape. The black hole has a one-way surface, called an event horizon, into which objects can fall, but out of which nothing can come. It is called "black" because it absorbs all the light that hits it, reflecting nothing, just like a perfect black-body in thermodynamics.

A black hole is often defined as an object whose escape velocity exceeds the speed of light. This picture is qualitatively wrong, but provides a way of understanding the order of magnitude for the black hole radius.

The escape velocity is the minimum speed at which an object needs to travel so as to escape a source of gravity without falling back into orbit before stopping. On the earth, the escape velocity about 11.2 km/s, no matter what the object is, whether a bullet or a baseball, it must go at least 11.2 km/s to avoid falling back to the Earth's surface.

To calculate the escape velocity in Newtonian mechanics, consider a heavy object of mass M centered at the origin. A second object with mass m starting at distance r from the origin with speed v, trying to escape to infinity, needs to have just enough kinetic energy to make up for the negative gravitational potential energy, with nothing left over:

(where G is the gravitational constant). That way, as it gets closer to it has less and less kinetic energy, finally ending up at infinity with zero speed.

This relation gives the critical escape velocity v in terms of M and r. But it also says that for each value of v and M, there is a critical value of r so that a particle with speed v is just able to escape:

When the velocity is equal to the speed of light, this gives the radius of a hypothetical Newtonian dark star, a Newtonian body from which a particle moving at the speed of light cannot escape. In the most commonly used convention for the value of the radius of a black hole, the radius of the event horizon is equal to this Newtonian value.

 
The velocity necessary to escape from an object's gravitational field (called the object's escape velocity) depends on how dense the object is; that is, the ratio of its mass to its volume. A black hole forms when an object is so dense that, within a certain distance of it, even light is not fast enough to escape, since the speed of light is slower than the black hole's escape velocity. Unlike in Newtonian gravity, in general relativity, light going away from a black hole doesn't slow down and turn around. The Schwarzschild radius is still the last distance from which light can escape to infinity, but outgoing light which starts at the Schwarzschild radius doesn't go out and come back, it just stays there. Inside the Schwarzschild radius, everything must move inward, getting crushed somehow at the center.

In general relativity, the black hole's mass can be thought of as concentrated at a singularity, which can be a point, a ring, a light-ray, or a sphere; the exact details are not currently well understood in all circumstances. Surrounding the singularity is a spherical boundary called the event horizon. The event horizon marks the 'point of no return,' a boundary beyond which matter and radiation inevitably fall inwards, towards the singularity. The distance from the singularity at the center to the event horizon is the size of the black hole, and is equal to twice the mass in units where G and c equal 1.

CLASSIFICATION OF BLACK HOLE :

-BY MASS:

Class                                                             
>Supermassive black hole

            mass :  ~105–109 MSun                size : ~0.001–10 AU

>Intermediate-mass black hole    

            mass : ~103 MSun                           size :   ~103 km = REarth

>Stellar-mass                        

            mass :    ~10 MSun                           size : ~30 km

>Micro black hole                   

            mass : up to ~MMoon                      size : up to ~0.1 mm

 <-- supermassive black hole

                                      intermediate-mass black hole -->

 <-- stellar-mass black hole         

                                                                    micro black hole -->

super conductivity

OW YEAH!!!!!

ALFRED COMES BACK!

wew, 

I think blogging is easy... But, in fact It's really hard

After 2 days (or more) thinking a new topic, 

now, 

ALFRED COMES WITH NEW TOPIC.......

(HAHAHAHAHAHAHA)

Ok, 

WE START NOW...

 
Hm...

Did you ever heard "SUPER CONDUCTIVITY"??

Super conductivity is a phenomenon occuring in a certain materials generally at very low temperatures, characterized by exactly zero electrical resistance and the exclusion of the interior magnetic field <Meissner effect>

The Meissner effect (1933, Walther Meissner and Robert Ochsenfeld) is the expulsion of a magnetic field from a superconductor. Walther Meissner and Robert Ochsenfeld discovered the phenomenon in 1933 by measuring the magnetic field distribution outside tin and lead samples. The samples, in the presence of an applied magnetic field, were cooled below what is called their superconducting transition temperature. Below the transition temperature the samples cancelled all magnetic field inside, which means they became perfectly diamagnetic. They detected this effect only indirectly; because the magnetic flux is conserved by a superconductor, when the interior field decreased the exterior field increased. The experiment demonstrated for the first time that superconductors were more than just perfect conductors and provided a uniquely defining property of the superconducting state.

There is not just one criterion to classify superconductors. The most common are:
*By their physical properties: they can be Type I (if their phase transition is of first order) or Type II (if their phase transition is of second order).
*By the theory to explain them: they can be conventional (if they are explained by the BCS theory or its derivatives) or unconventional (if not).
*By their critical temperature: they can be high temperature (generally considered if they reach the superconducting state just cooling them with liquid nitrogen, that is, if Tc > 77 K), or low temperature (generally if they need other techniques to be cooled under their critical temperature).
*By material: they can be chemical elements (as mercury or lead), alloys (as niobium-titanium or germanium-niobium), ceramics (as YBCO or the magnesium diboride), or organic superconductors (as fullerenes or carbon nanotubes, which technically might be included between the chemical elements as they are made of carbon).

THAT'S ALL ABOUT SUPERCONDUCTOR.... I MAKE IT SHORT BECAUSE TOO MANY TO EXPLAIN ABOUT THIS (ESPECIALLY THE MEISSNER EFFECT)

HAHAHA.....

SEE YA ....

ALFRED & YAHA

solar eclipse

hello, i'm alfred... this time I'll explain about solar eclipse...


See, this picture is a total solar eclipse.. solar eclipse is the most beautiful panorama about space....... if you hear about solar eclipse, you must see it, don't miss it... of course you don't want to lost a golden chance right?





do you ever seen this picture??? this is the picture of the longest duration for solar eclipse . this is the specific information of the picture above :

date : july 22,2009

duration : 398 s (6 min 38.8 s)

location : pacific ocean

time :Partial eclipse 23:58:18 (Jul 21)
Total eclipse 00:51:16
Central eclipse 00:54:31
Greatest eclipse 02:35:21
Totality was visible in many large cities, including Surat, Vadodara, Bhopal, Varanasi, Patna, Gaya, Dinajpur, Siliguri, Guwahati, Tawang in India and Chengdu, Nanchong, Chongqing, Yichang, Jingzhou, Wuhan, Huanggang, Hefei, Hangzhou, Wuxi, Huzhou, Suzhou, Jiaxing, Ningbo, Shanghai, Chapai Nawabganj as well as over the Three Gorges Dam in China. According to NASA, the Japanese island Kitaio Jima was predicted to have the best viewing conditions featuring both longer viewing time (being the closest point of land to the point of greatest eclipse) and lower cloud cover statistics than all of continental Asia.



ok, that's one of the example of solar eclipse
A solar eclipse occurs when the moon passes between the Sun and the Earth so that the Sun is fully or partially covered. This can only happen during a new moon, when the Sun and Moon are in conjunction as seen from the Earth. At least two and up to five solar eclipses can occur each year on Earth, with between zero and two of them being total eclipses. Total solar eclipses are nevertheless rare at any location because during each eclipse totality exists only along a narrow corridor in the relatively tiny area of the Moon's umbra.



There are four types of solar eclipses:
==>A total eclipse occurs when the Sun is completely obscured by the Moon. The intensely bright disk of the Sun is replaced by the dark silhouette of the Moon, and the much fainter corona is visible. During any one eclipse, totality is visible only from at most a narrow track on the surface of the Earth.

==>An annular eclipse occurs when the Sun and Moon are exactly in line, but the apparent size of the Moon is smaller than that of the Sun. Hence the Sun appears as a very bright ring, or annulus, surrounding the outline of the Moon.

==>A hybrid eclipse (also called annular/total eclipse) transitions between a total and annular eclipse. At some points on the surface of the Earth it is visible as a total eclipse, whereas at others it is annular. Hybrid eclipses are comparatively rare.

==>A partial eclipse occurs when the Sun and Moon are not exactly in line and the Moon only partially obscures the Sun. This phenomenon can usually be seen from a large part of the Earth outside of the track of an annular or total eclipse. However, some eclipses can only be seen as a partial eclipse, because the umbra never intersects the Earth's surface, passing above or below the Earth's polar regions.



Viewing the Sun during partial and annular eclipses (and during total eclipses outside the brief period of totality) requires special eye protection, or indirect viewing methods. The Sun's disk can be viewed using appropriate filtration to block the harmful part of the Sun's radiation. Sunglasses do not make viewing the sun safe. Only properly designed and certified solar filters should ever be used for direct viewing of the Sun's disk. Especially, self-made filters using common objects like a floppy disk removed from its case, a Compact Disc, a black colour slide film, etc. must be avoided despite what may have been said in the media

The safest way to view the Sun's disk is by indirect projection. This can be done by projecting an image of the disk onto a white piece of paper or card using a pair of binoculars (with one of the lenses covered), a telescope, or another piece of cardboard with a small hole in it (about 1 mm diameter), often called a pinhole camera. The projected image of the Sun can then be safely viewed; this technique can be used to observe sunspots, as well as eclipses. However, care must be taken to ensure that no one looks through the projector (telescope, pinhole, etc.) directly. Viewing the Sun's disk on a video display screen (provided by a video camera or digital camera) is safe, although the camera itself may be damaged by direct exposure to the Sun. The optical viewfinders provided with some video and digital cameras are not safe. Securely mounting #14 welder's glass in front of the lens and viewfinder protects the equipment and makes viewing possible. Professional workmanship is essential because of the dire consequences any gaps or detaching mountings will have. In the partial eclipse path one will not be able to see the spectacular corona or nearly complete darkening of the sky, yet, depending on how much of the sun's disk is obscured, some darkening may be noticeable. If two-thirds or more of the sun is obscured, then an effect can be observed by which the daylight appears to be dim, as if the sky were overcast, yet objects still cast sharp shadows.





It is safe to observe the total phase of a solar eclipse directly with the unaided eye, binoculars or a telescope, when the Sun's photosphere is completely covered by the Moon. During this period the sun is too dim to be seen through filters. The Sun's faint corona will be visible, and the chromosphere, solar prominences, and possibly even a solar flare may be seen. However, viewing the Sun after totality can be dangerous.

Baily's beads.


When the shrinking visible part of the photosphere becomes very small, Baily's beads will occur. These are caused by the sunlight still being able to reach Earth through lunar valleys, but no longer where mountains are present. Totality then begins with the diamond ring effect, the last bright flash of sunlight.

At the end of Totality, the same effects will occur in reverse order, and on the opposite side of the moon.



Artificial satellites can also pass in front of, or transit, the Sun as seen from Earth, but none are large enough to cause an eclipse. At the altitude of the International Space Station, for example, an object would need to be about 3.35 km across to blot the Sun out entirely. These transits are difficult to watch, because the zone of visibility is very small. The satellite passes over the face of the Sun in about a second, typically. As with a transit of a planet, it will not get dark.

Artificial satellites do play an important role in documenting solar eclipses. Images of the umbra on the Earth's surface taken from Mir and the International Space Station are among the most spectacular eclipse images in history. Observations of eclipses from satellites orbiting above the Earth's atmosphere are of course not subject to weather conditions.

The direct observation of a total solar eclipse from space is rather rare. The only documented case is Gemini 12 in 1966. The partial phase of the 2006 total eclipse was visible from the International Space Station. At first, it looked as though an orbit correction in the middle of March would bring the ISS in the path of totality, but this correction was postponed.



ok.... that's all....
see you on the next blog

Alfred & ~YaHa