what exactly is a nebula?
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a nebula is any cloud of interstellar gas or plasma and dust.  there several kinds.  emission nebulae are clouds of hot interstellar gas or plasma and dust.  the gas atoms in the cloud become ionized, and the atoms emit visible light when the ions and electrons recombine.  reflection nebulae are clouds of cool gas and dust which reflect the light of nearby stars.  they do not emit any light.  dark nebulae are clouds of cool gas and dust and do not emit any light, but they obscure more distant light sources.\n\nhttp://en.wikipedia.org/wiki/Nebula
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STARS AND NEBULAE.\n\nMost of the things you can see in the night sky are stars: a few thousand are visible to the unaided eye. A star is a hot ball of mostly hydrogen gas; the Sun is an example of a typical, ordinary star. Gravity keeps the gas from evaporating into space, and pressure due to the star's high temperature and density keeps the ball from shrinking. In the core of the star, the temperature and densities are high enough to sustain nuclear fusion reactions, and the energy produced by these reactions works its way to the surface and radiates into space as heat and light. When the fuel for the fusion reactions is depleted, the structure of the star changes. The process of building up heavier elements from lighter ones by nuclear reactions, and adjusting the internal structure to balance gravity and pressure, is called stellar evolution. \nLooking at a star through a telescope can tell us many of its important properties. The color of a star tells us its temperature, and the temperature depends on some combination of the star's mass and evolutionary phase. Usually, observations also allow us to find the luminosity of the star, or the rate at which it radiates energy as heat and light. \nAll stars visible to the unaided eye are in our galaxy, the Milky Way. The Milky Way is system of roughly 100 billion stars, along with a great deal of interstellar material. The galaxy is shaped like a flattened disk embedded in a round, faint halo. Gravity keeps the stars from drifting away, and the motions of the stars keep the system from falling in on itself. The Milky Way has no distinct edge - the distribution of stars tapers off gradually with increasing distance from the center. The SDSS detects stars more than a million times fainter than can be seen with the unaided eye, far enough to see the outer structure of the Milky Way. \nStar Colors and Luminosities: The H-R Diagram\nAstronomers often make plots of the luminosities of stars compared to their colors. The first such charts were made in the early twentieth century, when astronomers took spectra of thousands of stars, then placed the spectra into a sequence based on the appearance of several different features. The classes of stars were given different letters as names; in order of decreasing temperature, they are OBAFGKMLT. The hottest stars are class O, while the coolest are class T. Two astronomers, Ejnar Hertzsprung and Henry Norris Russell, independently started to wonder what would happen if they compared stars' luminosities to their spectral classifications (or, alternatively, to their temperatures). They knew that some stars were hotter and more luminous than the sun, and that others were cooler and less luminous. Hertzsprung and Russell found that 90% of the stars fell into a narrow band they termed the "main sequence." Today, we call this type of plot a Hertzsprung-Russell (or H-R) diagram. \nAstronomers further divide each letter into ten categories from 0 to 9, with 0 being the hottest star in that spectral class and 9 being the coolest. So, a B1 star is hotter than a B2 star, and a B9 star is hotter than an A0 star. Our own sun is at the "hot" end of the G range with a surface temperature of 5,770° K; therefore, it's called a G2 star. \nSpectral classes give us a convenient way to refer to most types of stars - from O0, the hottest at over 25,000° K, down to T9, the coolest failed stars at 1,000° K. Each spectral type of star is associated with a specific color: all G-type stars like the sun are yellow, all M-type stars appear red, and all B-type stars are bluish. Thus, this system of letters and numbers tells us where a star is on the horizontal (color or temperature) axis of the H-R diagram. \nTwo alternative systems tell us approximately where on the vertical (luminosity) axis a star can be found. One system uses absolute magnitude, a measure of luminosity derived from the apparent magnitude, or brightness of the star
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The main reason is dust in space that absorbs the light.  For instance, we are in a great big spiral galaxy.  Generally, if you look at a spiral galaxy, you see an immense, bright core.  So why don't we see such a core?  It's because of the dust.  The core, if visible, should be right around the constellation of Sagitarius.  But since there's so much dust in the plane of the galaxy, we can't see it in the invisible spectrum.  Astronomers have managed to infer the direction of the center of the galaxy by looking for a type of light (21 cm radiation) that is regualrly produced by astronomical phenomena, and which has an ability to pass more easily through the clouds of dust in space.  By gauging the direction of most of this radiation, they can infer that the bulk of the galaxy is in the direction of Sagitarius.\n\nAnd really, there is "light" coming from all directions, but most of it isn't in the visible range.  Cosmologists have found what is refered to as the 3K (three "degrees" Kelvin--a very cold temperature) radiation background that exists in direction.  This is seen not as the product of stars, but as a remnant of the big bang.\n\nBut most importantly, there are not really "infinite" stars.  The universe, though boundless, is not truly infinite.  There are some mathematical oddities that you find when you try to deal with the infinite and the boundless.  For instance, there are an infinite number of poritive integers, and there are an infinite number of irrational numbers between 0 and 1.  As odd as it seems, there are actually more irrational numbers between 0 and 1 (what my math professor called the "uncountably infinite") than there are positive integers (so-called "countably infinite").  Due to the relativity of simultneity shown by Einstein, one cannot exactlt quantify the total number of stars in the universe at a given point in time, because an observer moving at a different speed and looking at that moment in time would disagree as to which stars had already exploded or not, and which stars had already formed or not.  So while you can really make a definitive statement as to the number of stars, the number is not really infinite in the general sense of the word, as neither is the universe truly infinite.
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A supernova (pl. supernovae) is a stellar explosion which produces an extremely bright object made of plasma that declines to invisibility over weeks or months. A supernova briefly outshines its entire host galaxy. It would take 10 billion years for the Sun to produce the energy output of an ordinary Type II supernova.[1]. The Sun is notably too small to ever become a supernova—rather it will become a White Dwarf (see Chandrasekhar limit).\n\nThere are several different types of supernovae and two possible routes to their formation. A massive star may cease to generate fusion energy from fusing the nuclei of atoms in its core, and collapse under the force of its own gravity to form a neutron star or black hole. Alternatively, a white dwarf star may accumulate material from a companion star until it nears its Chandrasekhar limit and undergoes runaway nuclear fusion in its interior, completely disrupting it. This second type of supernova is distinct from a surface thermonuclear explosion on a white dwarf, which is called a nova. In either type of supernova, the resulting explosion expels much or all of the stellar material with great force.[2]\n\nThe explosion drives a blast wave into the surrounding space, forming a supernova remnant. One example of this process is the remnant of SN 1604, shown to the right.\n\n"Nova" is Latin for "new", referring to what appears to be a very bright new star shining in the celestial sphere; the prefix "super" distinguishes this from an ordinary nova, which also involves a star increasing in brightness, though to a lesser extent and through a different mechanism.
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At least 100 billion galaxies are known to exist in the Universe. Our galaxy is a spiral one, so in terms of structure it consists of galactic core and several spiral arms. In terms of composition it includes stars, planets (made from regular matter, including atoms of all naturally occurring elements and ions), galactic gas and dust (made from regular matter, mostly hydrogen and helium as far as the gas goes, and hydrogen, carbon, silicon, oxygen and some other elements as far as the dust goes), dark matter and dark energy (there is little known about the last two).
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You've probably seen the pictures of a grid with a giant funnel extending infinitely downward.  That's not the shape of the hole itself, but a map of the curvature of space near the singularity.  The singularity, or "hole" itself is a point of infinitely large density and infinitely small size.
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A meteoroid is a relatively small (sand- to boulder-sized) fragment of debris in the Solar System. When entering a planet's atmosphere, the meteoroid heats up and partially or completely vaporizes. The gas along the path of the meteoroid becomes ionized and glows. The trail of glowing vapor is called a meteor, or shooting star. If any portion of the meteor survives to reach the ground, it is then referred to as a meteorite.79% of meteorites are Chondrites - balls of mafic minerals with small grain size indicative of rapid cooling. In most chondrites small spherules, called chondrules, can be found. Chondrites are typically about 4.6 billion years old and are thought to represent material from the asteroid belt. It is unknown how they formed. Carbonaceous Chondrites, thought to be unaltered solar nebula material, constitute about 5% of meteorites and contain small amounts of organic materials, including amino acids. Also, presolar grains are identified in carbonaceous chondrites. The isotope ratios of carbonaceous chondrites are similar to those of the Sun.Achondrites are similar to terrestrial mafic igneous rocks and sometimes are brecciated. Achondrites constitute about 8% of the incoming material and are thought to represent crustal material of larger asteroids. About 6% of meteorites are iron meteorites with intergrowths of iron-nickel alloys, such as kamacite. Unlike chondrites, the crystals are large and appear to represent slow crystallization. Iron meteorites are thought to be the core material of one or more planets that subsequently broke up. Stony iron meteorites constitute the remaining 2%. They are a mixture of iron-nickel and silicate minerals. They are thought to have originated in the boundary zone above the core regions where iron meteorites originated. A small number of meteorites belong to additional groups or subgroups with unique chemical characteristics relative to other members of the larger groups, such as Lunar meteorites or Martian meteorites.
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Hot gas in the Universe swirls together sometimes and forms a nebula. A nebula is like a VERY big cloud in space that swirls together over millions of years and cools down a little. The gas swirls and cools together tighter and tighter until the gas starts to form lumps . . BIG lumps . . .HOT lumps . . .big hot lumps that swirled and spun around. Our Sun is one of those lumps. Our Sun is a star. When the Sun was still a spinning lump, parts of it splashed off of it as it spun around. Those small lumps of hot gas were flung into cold space and cooled down and became less hot gas and more like lava. The smaller lumps kept spinning and cooling down until they became planets. The planets float around the Sun, captured in her invisible tentacles of gravity. We call a Sun and her family of planets a "solar system". There are millions and millions and millions of solar systems in the Universe. The hot gas that first made the cloud nebulas started out as energy or light. Tiny bundles of that energy formed and we call those bundles, "photons". Photons come together to form matter, like the atoms of gas. Here is a real picture that we have made of the beginning of the Universe when all that energy first appeared:\nhttp://www.princeton.edu/pr/pwb/03/0217/\n\nHere is a picture of a nebula:\nhttp://www.saskschools.ca/~gregory/space/sp/nebula.jpg\n\nStar formation website:\nhttp://sscws1.ipac.caltech.edu/Imagegallery/subcat.php?cat=Astronomical_Images&subcat=Star_Formation
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astrophysics\n\nn : the branch of astronomy concerned with the physical and chemical properties of celestial bodies
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Actually you could see right through the nebula. Nebulae are extremely thin and much clearer than the air on clearest day on Earth. The only reason we can see them at all is that they are trillions of miles thick. It wouldn't be like the movies at all, where the space ship is hidden in a dense fog, it would be more like space looking clear but the stars appearing somewhat dimmer. So you could just triangulate on a number of known stars outside the nebula to determine your position.
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kinda, but it isn't a star. it's fragments of space debris, meteors etc, burning up whilst passing thru the earth's atmosphere. From the ground it appears like a star shooting across the sky, hence it's name.
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Self gravitation is thought to have been the main cause of the collapse of the solar nebula.  \n\nIn addition, there is some evidence (from isotopic analyses of primitive meteorites) for the addition to the nebula of elements that were produced by nucleosynthesis in a supernova "shortly" before the aggregation of  nebular material into macroscopic solid bodies.  A pressure wave associated with the arrival of this supernova material may have been triggered or accelerated the collapse.  More recent research, however, suggests that at least some of the isotopic anomalies that gave rise to this idea may have been produced by irradiation of solar nebular material by the sun itself, rather than from an extrasolar event.
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A galaxy is a huge gravitationally bound system of stars, interstellar gas and dust, plasma, and (possibly) unseen dark matter. Typical galaxies contain 10 million to one trillion (107 to 1012) stars, all orbiting a common center of gravity. In addition to single stars and a tenuous interstellar medium, most galaxies contain a large number of multiple star systems and star clusters as well as various types of nebulae. Most galaxies are several thousand to several hundred thousand light years in diameter and are usually separated from one another by distances on the order of millions of light years.\n\nAlthough so-called dark matter appears to account around 90% of the mass of most galaxies, the nature of this unseen components is not well understood. There is some evidence that supermassive black holes may exist at the center of many, if not all, galaxies.\n\nIntergalactic space, the space between galaxies, is filled with a tenuous plasma with an average density less than one atom per cubic meter. There are probably more than a hundred billion (1011) galaxies in the visible universe.
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Fifteen minutes since you asked your question and nobody has taken a shot at an answer. That's a pretty good indication that there isn't one, neither a known birth-place nebula for Sirius nor an answer. In researching your question, I did find a photo of the Sirius system and a nebula is clearly visible, but apparently it has no specific name or designation.\n\nhttp://www.solstation.com/stars/sirius2.htm
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the Horse Head Nebula looks exactly like its namesake!  Beautiful.
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No hope when climate conditions improve here I get a good pic\n\n(cited below)Messier 17, (NGC 6618) Swan or Omega Nebula, is a very bright nebulous area at the northern extreme of Sagittarius, close by the border with Serpens Cauda. It is also variously known as the Swan Nebula (from its inverted appearance), the Omega Nebula, or the Horseshoe Nebula. The central bar-like mass of emission nebulosity has a very high surface brightness and is easily seen in binoculars. The outer parts are much fainter and extend over a comparatively wide area. Unusually there are no obvious bright stars fuelling the vigorous ionization of gases, but it has been suggested that there are hot stars embedded deep within the nebulous region. M17 is about 5,000 light years distant. It was probably first seen by the Swiss astronomer P.L. de Cheseaux in the spring of 1764 and was found and catalogued independently by Charles Messier in June of the same year.\n\nDate: 15/06/02 (R Luminance only: G, B were from 14/06/02)\nLocation: Southern France\nConditions: calm, transparency=8, seeing=9 (zero Jetstream)\nOptics: RCOS Ritchey-Chretien 12.5" f/9 working at f/6.7 with AP x.75 focal reducer.\nMount: AP 900 GTO on Portable Pier\nCamera: SBIG ST-8E / CFW-8\nGuiding: Integral ST-8E guiding chip controlled via MaximCCD\nExposure: High resolution R/RGB (no binning): 40/40:40:60 minutes\n\nProcessing: Image acquisition, calibration, combining, and DDP were applied using Maxim DL. Deconvolution was applied using AIP. Registration of Luminance and RGB images done using Registar, with and final image adjustments applied in Photoshop.
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when a star explodes into a nebulae its then has black holes in or around it causing vacuum. its once magnetic field still pulsates letting off higher frequency waves that we can pickup this a quasar ones that are further out or that have cooled off over 15,000yrs still give off these pulses thus pulsar. And about your light to another plane or dimension or a light source for  another planet