Saturday, August 29, 2009
Gum Nebula(Gum 12) is a round, large nebula. It is so large, yet hardly visible against a bright and complex background; its front edge is as close to us as 450 light-years, while its back edge lies about 1,500 light-years away.
The Gum Nebula is believed to be the hugely expanded remains of a supernova that took place around a million years ago. It contains the Vela OB2 Association, the hot stars of which cause it to shine. Also embedded in the Gum are the Vela Supernova Remnant and the Vela Pulsar.
It is named after its discoverer, the Australian astronomer Colin Stanley Gum, who published his findings in 1955.
Thursday, August 27, 2009
The Lagoon Nebula Messier 8 (M8, NGC 6523) is one of the finest and brightest star-forming regions in the sky. It is a giant cloud of interstellar matter which is currently undergoing vivid star formation, and has already formed a considerable cluster of young stars. It was independently noted as a "nebula" by John Flamsteed about 1680, who cataloged it as his No. 2446. Flamsteed's position is close to that later determined by Messier and near the center of the nebula, while the young open cluster, which was later cataloged as NGC 6530, is situated on the Eastern half of M8. This object was again seen by Philippe Loys de Chéseaux in 1746, who could resolve some stars and consequently classified it as a cluster. One year later, in 1747, it was observed by Guillaume Le Gentil. When Charles Messier cataloged this object on May 23, 1764, he primarily described the cluster, and mentioned the nebula separately as surrounding the star 9 Sagittarii; his original position is closer to the modern position of the cluster than to that of the nebula.
One of the remarkable features of the Lagoon Nebula is the presence of dark nebulae known as 'globules' which are collapsing protostellar clouds. Some of the more conspicuous globules have been cataloged in E.E. Barnard's catalog of dark nebulae: Barnard 88 (B 88), the comet-shaped globule extended North-to-South (up-down) in the left half and near top of our image, small B 89 in the region of cluster NGC 6530, and long, narrow black B 296 at the south edge of the nebula (lower edge of the image).
Within the brightest part of the Lagoon Nebula, a remarkable feature can be seen, which according to its shape is called the "Hourglass Nebula". This feature was discovered by John Herschel and occurs in a region where a vivid star formation process appears to take place currently; the bright emission is caused by heavy excitation of very hot, young stars, the illuminator of the hourglass is the hot star Herschel 36.
The young open cluster NGC 6530 associated with the Lagoon Nebula M8 was classified as of Trumpler type "II 2 m n", meaning that it is detached but only weakly concentrated toward its center, its stars scatter in a moderate range of brightness, it is moderately rich (50--100 stars), and associated with nebulosity (certainly, with the Lagoon nebula). As the light of its member stars show little reddening by interstellar matter, this cluster is probably situated just in front of the Lagoon Nebula. Its brightest star is a 6.9 mag hot O5 star, and Eichler gives its age as 2 million years.
These are three Nebula found in Sagittarius. M8 (the Lagoon Nebula) and M20 (the Trifid). The Nebula in the upper right hand corner is NGC 6559 (which did not make Messier's list). This is a false color photo, with a color scheme apparently made common by the HUbble Telescope. The color scheme works for land based telescopes because it allows the astronomer to ignore urban light pollution. M8 is 30 light years LONG and around 5000 light years away.
The centre of the Lagoon Nebula is a whirlwind of spectacular star formation. Visible on the upper left, at least two long funnel-shaped clouds, each roughly half a light-year long, have been formed by extreme stellar winds and intense energetic starlight. The tremendously bright nearby star, Hershel 36, lights the area. Vast walls of dust hide and redden other hot young stars. As energy from these stars pours into the cool dust and gas, large temperature differences in adjoining regions can be created generating shearing winds which may cause the funnels. This picture, spanning about 5 light years, was taken in 1995 by the orbiting Hubble Space Telescope.
Sunday, August 2, 2009
Saturday, August 1, 2009
SN 1054 (Crab Supernova) was a supernova that was widely seen on Earth in the year 1054. It was recorded by Chinese, Japanese, and Persian/Arab astronomers as being bright enough to see in daylight for 23 days and was visible in the night sky for 653 days.The progenitor star was located in the Milky Way galaxy at a distance of 6,300 light years and exploded as a core-collapse supernova.
The Crab Nebula consists of a broadly oval-shaped mass of filaments, about 6 arcminutes long and 4 arcminutes wide surrounding a diffuse blue central region. The filaments are the remnants of the progenitor star's atmosphere, and consist largely of ionised helium and hydrogen, along with carbon, oxygen, nitrogen, iron, neon and sulfur.
The Crab Nebula is currently expanding outwards at about 1,500 km/s. Images taken several years apart reveal the slow expansion of the nebula, and by comparing this angular expansion with its spectroscopically determined expansion velocity, the nebula's distance can be estimated. In 1973, an analysis of many different methods used to compute the distance to the nebula reached a conclusion of about 6,300 light years. Along its longest visible dimension, it measures about 13 ± 3 light years across.
Tracing back its expansion consistently yields a date for the creation of the nebula several decades after 1054, implying that its outward velocity has accelerated since the supernova explosion. This acceleration is believed to be caused by energy from the pulsar that feeds into the nebula's magnetic field, which expands and forces the nebula's filaments outwards.
At the center of the Crab Nebula are two faint stars, one of which is the star responsible for the existence of the nebula. The region around the star was found to be a strong source of radio waves in 1949 and X-rays in 1963, and was identified as one of the brightest objects in the sky in gamma rays in 1967. Then, in 1968, the star was found to be emitting its radiation in rapid pulses, becoming one of the first pulsars(Pulsars are sources of powerful electromagnetic radiation, emitted in short and extremely regular pulses many times a second.) to be discovered.
Electric Wizard "Dopethrone"