What is Nebula: Definition and 47 Discussions

A nebula (Latin for 'cloud' or 'fog'; pl. nebulae, nebulæ or nebulas) is an interstellar cloud of dust, hydrogen, helium and other ionized gases. Originally, the term was used to describe any diffused astronomical object, including galaxies beyond the Milky Way. The Andromeda Galaxy, for instance, was once referred to as the Andromeda Nebula (and spiral galaxies in general as "spiral nebulae") before the true nature of galaxies was confirmed in the early 20th century by Vesto Slipher, Edwin Hubble and others.
Most nebulae are of vast size; some are hundreds of light-years in diameter. A nebula that is visible to the human eye from Earth would appear larger, but no brighter, from close by. The Orion Nebula, the brightest nebula in the sky and occupying an area twice the angular diameter of the full Moon, can be viewed with the naked eye but was missed by early astronomers. Although denser than the space surrounding them, most nebulae are far less dense than any vacuum created on Earth – a nebular cloud the size of the Earth would have a total mass of only a few kilograms. Many nebulae are visible due to fluorescence caused by embedded hot stars, while others are so diffused that they can be detected only with long exposures and special filters. Some nebulae are variably illuminated by T Tauri variable stars.
Nebulae are often star-forming regions, such as in the "Pillars of Creation" in the Eagle Nebula. In these regions, the formations of gas, dust, and other materials "clump" together to form denser regions, which attract further matter, and eventually will become dense enough to form stars. The remaining material is then believed to form planets and other planetary system objects.

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  1. O

    What is the density of the Carina Nebula?

    In a James Webb photo thread, someone posted that the Carina Nebula has a density of a few atoms per cubic meter. This seems off to me, as this is close to the average density of the intergalactic medium of one atom per cubic meter, which is much less than the interstellar medium average density...
  2. N

    B Do emission nebula glow because of ionised or excited electrons?

    I'm trying to figure out why emission nebulae glow. I read various sites such as a NASA website explaining why they shine; 'The massive stars embedded within the nebula give off enormous amounts of ultraviolet radiation, ionizing the gas and causing it to shine.' The Britanica article on...
  3. agnimusayoti

    Calculating the Solid Angle of a Nebula from Earth

    If I assume the nebula is a circle, than the length of arc viewed from Earth is a half of the circumference. So, here $$l = \frac{1}{2} \pi D$$ From the problem, ##D = 125 000 ly##. Because the distance of nebula is much larger than the diameter; I try to approximate R with the distance of...
  4. Comeback City

    I Angular Momentum in a Solar Nebula

    Hello all! Hope everyone's been doing well! My question relates to the nebular theory of solar system formation. It is generally accepted that via the nebular hypothesis, matter in a nebula contracts on its own gravity and begins to spin, but I'm having trouble understanding why it must begin...
  5. angela6884

    B Creating an Interstellar Dust Nebula Experiment: Tips and Tricks for Success

    My experiment would need different composition of grains which would be ice, iron filings, and silicate shavings to act as the interstellar dust. I would drop these small particles(hopefully they will fall slowly) in a box and shut the lid quickly. Inside the box there will be a lightbulb acting...
  6. J

    I I use an Olll filter to view emission nebula -- how do they work?

    I use an Olll filter to view emission nebula such as the Great Nebula in Orion. What is the mechanism by which Olll in such nebula emit photons of the wavelength that passes through my filter?
  7. Solomei

    B Our solar system and its fellows

    Hello, I am new to this forum, so be brutal :) So, I've tried to find information about Earth's origin. The nebula, cluster we are a part of etc. but i could not find the answer I was looking for. For me, it seems logical that we are a part of a cluster. How often do we find a star whos just...
  8. J

    Nebulosity of an O Star (Homework Question)

    1. Question Suppose you examined the spectrum of some nebulosity surrounding a main-sequence spectral-type O star and found that it contained no emission lines, only the continuous spectrum of the star. What conclusions could you draw about the nature of the interstellar material around that...
  9. spark802

    Stargazing North American nebula from this past summer

    I shot this from western Canada July of 2016. Processed this out of a single exp as i had trouble stacking my subs. 300 secs, guided, 80mm doublet, Modded Canon 550d. https://www.flickr.com/photos/49843779@N08/29239414483/in/dateposted/
  10. E

    I Solar System Origins: Angular Momentum Problem?

    Hi guys, This is basically a quick question to hopefully find some pointers on a topic I've been browsing the internet on to not much success. Basically the topic I'm trying to find more information on is the angular momentum problem with the "nebular hypothesis" of the formation of our solar...
  11. F

    I Why do nebulae tend to collapse into discs?

    As far as I understand it, a nebula initially tends to have a small amount of rotation (on average) and then as it collapses under its own gravity this rotation increases significantly due to conservation of angular momentum (assuming that there is no external torque,right?!). What I'm unsure...
  12. M

    What if there was a black hole in the middle of a nebula?

    I was wondering, if there was a black hole in the center of a nebula, then would there be a possibility that the nebula would be eaten from the inside out before any stars could be born? It'd be something interesting to observe over time.
  13. Andy Resnick

    Witness the Majesty of the Ring Nebula: 100% Crop & (Nearly) Full Frame

    And lo, after 40 days and 40 nights of rain, a ball of fire in the sky did appear, and after it, a shimmering black velvet curtain of night. Ring nebula: 100% crop and (nearly) full frame: Deets: 800/5.6, 10s ISO 2000 exposures (total integration time 56 minutes). This is the first time...
  14. L

    Calculating relative velocity of Crab Nebula

    I'm using the the Doppler formula to calculate the relative velocity between the approaching and receding filaments of the crab nebula: Δλ/λnaught = v/c Change in wavelength/ wavelength = velocity/ speed of light I have reworked the formula as v= c(Δλ/λnaught) When I plug in the values I get...
  15. GiantSheeps

    Best way to see Andromeda galaxy

    I just recently got a dobsonian reflector telescope, (Orion SkyQuest XT8 PLUS Dobsonian Reflector Telescope) and I was wondering what the best way to see the andromeda galaxy would be using the telescope? Of these, which would be the best eye piece for that sort of thing?: Orion 2" 28mm...
  16. K

    How does a nebula form from a neutron star

    Here is my understanding, please correct me if I am wrong, thanks At the end of the giant stage of a star, it experiences a supernova explosion, and turns into a neutron star (could be pulsar) or black hole, the explosion releases a lot of its matter. Here is what I don't understand: 1...
  17. S

    Where Do Stars Form: Cool Nebulas or Hot Nebulas?

    Would you expect to find stars being made more easily in a cool, high-dense nebula or conversely a hot, high-dense nebula? Looking at for example the pillars of creation which is a stellar nursery, but what would be classified as hot and cold? relatively speaking. thoughts? thanks pf!
  18. M

    How do you find the temperature of the boomerang nebula?

    So i have a physics presentation to do on tuesday and i have no idea how to find the temperature of a of objects in space, specifically the boomeran nebula. I did some research and found stuff involving black body radiation, wiens law, and stefan boltzman law but i don't really understand it too...
  19. A

    M42 and the Running Man nebula with Takahashi 150mm

    First post on PF, thought I'd share my first serious attempt at astrophotography. I used itelescope since it's perpetual cloud cover where I'm at sadly, and all of my processing was done in Astroart. I learned a lot with this, but it's definitely an uphill struggle! M42 and the Running Man...
  20. D

    Distance to Crab Nebula.

    Homework Statement Hi. The Crab Nebula which can be seen with even a small telescope, is the result of a supernova. All parts of the nebula are moving away from the centre at 1.18*10^6 m/s. The angle that the Crab Nebula forms with the Earth is 0.083 degrees. This supernova was...
  21. skyshrimp

    Exploring the Cat's Eye Nebula's Activity

    I'm just learning about space. The Cat's Eye nebula looks very energetic at the core. I can see what looks like plasma firing off chaotically from the center star. If this was video footage, would what we see in this still Hubble photo move rapidly (like solar flares seen in footage...
  22. Sab95

    Evolution of a star from a nebula

    I know that our solar system and sun evolved from a nebula of a giant star.. but what happened to the remaining of the star.. entire star cannot go boom.! at least some remaining portion of the primordial star should have existed in the form of a neutron star or a white dwarf. If it existed what...
  23. V

    Angular Velocity of a Nebula Accretion Disk

    [SOLVED]Angular Velocity of a Nebula Accretion Disk [SOLVED] According to astronomy our solar system was created about 4.5 billion years ago when the nebula of an exploded supernova accreted to form a stellar mass known as our sun. They say that this "accretion disk" or mass of clumping...
  24. E

    How are panatery Nebula formed and when do they die

    My simple question is how are panatery nebula formed.. Al what i know is that after helium fusion is over, some complex process will occur leading to explosion which leads to the nebula... What are these complex processes...Moreover, it appears just like a core of a star surrounded by some...
  25. S

    Do all pulsars have a Pulsar wind nebula?

    Intuitively I would say no because it seems like a big call but at the same time the high energy effects rely on the interaction between magnetic fields and gas don't they? Any tips or just an idea of where I can find out would be awesome
  26. Dotini

    Surprising Gamma Rays From Crab Nebula

    http://www.bbc.co.uk/news/science-environment-15203788 Astronomers have spotted gamma ray emissions coming from the Crab Pulsar at far higher energies than expected. This challenges notions of how these powerful electromagnetic rays - like light, but far more energetic - are formed, researchers...
  27. Drakkith

    Photo of Orion Nebula Taken 2 Weeks Ago

    Hey all! Just sharing my photo of the Orion Nebula I managed to take about 2 weeks ago. Managed to get this sucker RIGHT before sunrise. Not the greatest picture ever, but I am proud of it. [PLAIN]http://img33.imageshack.us/img33/3486/m422.jpg
  28. S

    Is the Red Square Nebula MWC 922 Really a Hypercube?

    http://apod.nasa.gov/apod/ap070416.html http://apod.nasa.gov/apod/ap070416.html Found this yesterday on dailygalaxy.com. explanation given is that this is ejecta of two cones from a central star, seen edgewise. I am not convinced by that explanation for several reasons. My first thought...
  29. N

    Effect of pressure in a nebula?

    So... I'm trying my hand at programming an n-body simulation. For those of you unfamiliar, that is a simulation where every body attracts every other body. I have something effectively like this: http://www.youtube.com/watch?v=byI9yhITDsM" But now... these straightforward n-body simulations...
  30. Dotini

    Earth Not From Same Nebula as Sun. Huh?

    http://www.sciencedaily.com/releases/2011/06/110623145430.htm http://www.msnbc.msn.com/id/43513975/ns/technology_and_science-space/ This is either a hoax or colossal blunder from NASA, or it is the most disturbing news I've had all week. Apparently, we are cosmic orphans, adrift in an alien...
  31. C

    Volume of nebula needed to form a star with same number of atoms as sun

    1. Question: In one region of a nebula the mean separation of atoms is 2.3x10^-3 m. What volume of the nebula contains enough atoms to make a star, similar to the sun, of radius 7.0x10^8 m within which the mean distance between atoms is 1.0x10^-10m? 2. Volume of sphere 4/3(pi(r^3 ))...
  32. E

    Would a human be able to see a nebula if they were close enough?

    Would the human eye be able to pick up a picture from the Hubble Telescope unaided if it were close enough? For instance, how close would I have to be to the Pillars of Creation in order for it to fill my entire field of view if I were floating in outer space? I assume several hundred light...
  33. T

    Nebula powered spaceship?

    Homework Statement My question is obscure, but i had to ask. :smile: Lets say i built a ship that could hold the crab nebula(dimensions of the ship 15km*15km*20km). Now I want to use the nebula to power my ship somewhat like a flywheel. I would like to hear some possible solutions...
  34. J

    Astronomy Reflection nebula Question

    Homework Statement 1. If you looked at the spectrum of a reflection nebula, would you see absorption lines, emission lines, or no lines? Explain your answer. As part of your explanation, describe how the spectrum demonstrates that the light was reflected from nearby stars. Homework...
  35. S

    Thor's Helmet: Pre-Supernova with Emissions Nebula?”

    I read that Thor's helmet (NGC 2359) is in a pre-supernova stage, but there is an emissions nebula around it. How this possible if the star is hasn't gone supernova?
  36. M

    What are the actual dimensions of the Horsehead nebula?

    Hi, I was looking at information about the Horsehead nebula on wikipedia http://en.wikipedia.org/wiki/Horsehead_nebula and it says that its apparent dimensions are 8x6 arcmins. I'm not sure how to find the actual dimensions, say in light-years. Here's how I believe it should be, but...
  37. S

    What do I use to determine rotational speed of solar nebula?

    Hi there. I need some help with this I have confused myself ... I am trying to determin the rotational spped of our solar nebula as it would have been at r=40 000 AU. I have the facts that at 40 AU v=5km/second. what I am not sure on is do I use L=m*v*r? if so do I use the mass of the sun...
  38. F

    Solving the Expansion of the Crab Nebula

    Homework Statement The gas cloud known as the Crab Nebula can be seen with even a small telescope. It is the remnant of a supernova, a cataclysmic explosion of a star. The explosion was seen on the Earth on July 4, 1054 a.d. The streamers glow with the characteristic red color of heated...
  39. R

    How Does Electron Density Change Over Time in a Deionized Hydrogen Nebula?

    Homework Statement Consider a nebula of pure hydrogen which is completely ionized and in steady-state (# ionizations/sec = # recombinations/sec) at a constant temperature and density. Suppose the source of the ionizing radiation suddenly “turns off”. Find and graph the electron density as a...
  40. russ_watters

    Stargazing First is the Blue Snowball , a planetary nebula.

    First is the "Blue Snowball", a planetary nebula. I took three pictures tonight. First is the "Blue Snowball", a planetary nebula. This one is really bright and 30 second exposures are all that is really needed. The only stretching that was done was to cut off the black level at the...
  41. J

    Why are the emission lines in the Crab Nebula split into two?

    I'm doing a project on the Crab Nebula for my first-year astronomy class and I am finding the spectroscopy a bit puzzling. What I have read is that the normal emission line for a particular gas is split into two, one red shifted and one blue shifted. This of course is accounted for by the Dopler...
  42. V

    Exploring the Milky Way & Orion Nebula with Hubble

    http://spaceflightnow.com/news/n0601/09milkyway/ http://spaceflightnow.com/news/n0601/11hubbleorion/
  43. D

    Ring Nebula: Synchrotron Radiation & Magnetic Fields

    Is the beauty and color to the Ring Nebula due to synchrotron radiation of particles (electrons) with higher energy (spin) being blueshifted the closer they are to the white dwarf at the center? If so is it the magnetic field that spins the electrons intensly and the futher away the electrons...
  44. C

    Why Do Planetary Nebulae Form?

    Hi, When a white dwarf is formed, why do the outer layers of gas which made it a red giant drift away to foirm a planetary nebula? Decrease gravity? Outward pressure? What exactly? Also, when the outer layers of a star move outwards to form a red giant, why do they cool down? (hence...
  45. chroot

    Amateur astronomer finds new nebula

    http://news.bbc.co.uk/2/hi/science/nature/3479615.stm Wicked cool! I'm always very proud to hear of amateurs making serious scientific contributions! - Warren
  46. wolram

    Absolute zero for the boomerang nebula?

    hi, can anyone confirm the 1degree above absolute zero for the boomerang nebula?