Types of Nebula
By order in which they appear from top to bottom, left to right, here are the main types and some provided examples for visual reference:
Planetary Nebula: Sh2-188
Planetary nebulae are shells of gas thrown out by some stars near the end of their lives. Our Sun will probably evolve a planetary nebula in about 5 billion years. They have nothing at all to do with planets; the terminology was invented because they often look a little like planets in small telescopes. A typical planetary nebula is less than one light-year across.
Dark Nebula: LDN 1622
Dark nebulae are clouds of dust which are simply blocking the light from whatever is behind. They are physically very similar to reflection nebulae; they look different only because of the geometry of the light source, the cloud and the Earth. Dark nebulae are also often seen in conjunction with reflection and emission nebulae. A typical diffuse nebula is a few hundred light-years across.
Emission Nebula: NGC 896
Emission nebulae are clouds of high temperature gas. The atoms in the cloud are energized by ultraviolet light from a nearby star and emit radiation as they fall back into lower energy states (in much the same way as a neon light). These nebulae are usually red because the predominant emission line of hydrogen happens to be red (other colors are produced by other atoms, but hydrogen is by far the most abundant). Emission nebulae are usually the sites of recent and ongoing star formation.
Reflection Nebula: NGC 1333
Reflection nebulae are clouds of dust which are simply reflecting the light of a nearby star or stars. Reflection nebulae are also usually sites of star formation. They are usually blue because the scattering is more efficient for blue light. Reflection nebulae and emission nebulae are often seen together and are sometimes both referred to as diffuse nebulae.
Supernova Remnant: M1
Supernova Remnant - Supernova remnants are created when a star ends it life in a massive explosion known as a supernova. The explosion blows a large amount of the star’s matter out into space. This cloud of matter glows with the remains of the star that created it. One of the best examples of a supernova remnant is the crab Nebula (M1) in Taurus. It is illuminated by a pulsar which was created by the supernova.
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Known Exoplanets Orbiting Stars Near The Sun
Or Not …
Google Plus Science Lab | May 26, 2013
May 26, 2013
In the Milky Way galaxy, it is expected that there are many billions of planets, with many more free-floating planetary-mass bodies orbiting the galaxy directly. The nearest known exoplanet is Alpha Centauri Bb.
June 11, 2013
Writing in The Astrophysical Journal last month, Artie P. Hatzes, the director of the Thuringian State Observatory in Germany, reported that he could not confirm the planet when he went looking for it in the European data … That doesn’t mean the planet does not exist, Dr. Hatzes wrote, but “in my years of experience in extracting planet signals, this simply does not ‘smell’ like a real planet.”
Dr. Hatzes’s skepticism proved catching. Suzanne Aigrain of Oxford University quoted Carl Sagan’s dictum that extraordinary claims require extraordinary evidence, saying that Dr. Hatzes’s paper “certainly casts doubt on the original evidence.”
Read about Alpha Centauri Bb …
Almost all of the planets detected so far are within our home galaxy the Milky Way; however, there have been a small number of possible detections of extragalactic planets. Astronomers at the Harvard-Smithsonian Center for Astrophysics reported in January 2013, that “at least 17 billion” Earth-sized exoplanets are estimated to reside in the Milky Way galaxy.
(NASA) This might resemble a fried egg you’ve had for breakfast, but it’s actually much larger. In fact, ringed by blue-tinted star forming regions and faintly visible spiral arms, the yolk-yellow center of this face-on spiral galaxy, NGC 7742, is about 3,000 light-years across. About 72 million light-years away in the constellation Pegasus, NGC 7742 is known to be a Seyfert galaxy- a type of active spiral galaxy with a center or nucleus which is very bright at visible wavelengths. Across the spectrum, the tremendous brightness of Seyferts can change over periods of just days to months and galaxies like NGC 7742 are suspected of harboring massive black holes at their cores. This beautiful color picture is courtesy of the Hubble Space Telescope Heritage Project.
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For me, I am driven by two main philosophies, know more today about the world than I knew yesterday. And along the way, lessen the suffering of others. You’d be surprised how far that gets you.
Astronomers have discovered more than 800 exoplanets, with many more candidate worlds awaiting confirmation by follow-up observations. Most of them, however, are gas giants, similar to Jupiter, and only a handful have a solid surface and orbit their host stars in the habitable zone, and perhaps life as we know it, can exist.
But these uninhabitable exoplanets could host habitable exomoons. There is a habitable zone for exomoons, it’s just a little different than the habitable zone for exoplanets. Like Earth’s moon, many exomoons are tidally locked to their host planet, meaning one hemisphere is permanently turned away from the planet, which would constrain the habitable regions on the moon’s surface. Moons also have two sources of light — one from their star and the other from their host planet — and are subject to dramatic eclipses.
An observer standing on the surface of such an exomoon would experience day and night in a totally different way than we do on Earth. For instance, stellar eclipses could lead to sudden total darkness at noon.
Some researchers have already started thinking about how they might use instruments like the planet-hunting Kepler Space Telescope to detect alien moons. Variations in these brightness patterns might reveal the presence of a moon orbiting a planet.