Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Nebulas from close

  1. Dec 26, 2007 #1
    Merry christmas, and the stupid question of the day:
    How would, reallistically, a nebula look like from a close distance, say, within a fraction of an AU?

    I mention this because, in too many TV space shows, some spaceship hides into a nebula, as it would in a big cloud, which seems to me severely unrealistic.

    First, we see nebulas from an enormous distance. I see no reason to believe they would look just like that at a close range, just as the blur in a foggy day looks denser the farther. For all we know, we could be in the middle of one. Or not? Is there an estimate of the density of ions within a nebula?

    Second, there are violent processes associated with nebulas. Shouldn't we perceive them in movement, much as solar wind? Then again, the enourmity of the distances could cancel out the notion of movement, since, in order to be close to (some part of) something, you will probably be moving along with it. That is, if there is some "it" to be seen at a close range, in the first place.
  2. jcsd
  3. Dec 26, 2007 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    The Ring Nebula (M57) is about a light-year in diameter and is located some 2,000 light-years (3,500 ly according to UWashigton page) from Earth in the direction of the constellation Lyra.


    Nebulae are Big, really BIG!

    http://www.atlasoftheuniverse.com/nebulae/ngc2237.html - According to this - NGC2237 125 ly for size!

    Particle densities vary throughout a give nebula and among nebulae.
  4. Dec 26, 2007 #3
    Thanks for your answer, Astronuc.

    The links mention very little about particle density, thought a figure for mass density of the Ring nebula (for the entire nebula as an average, I guess) is given in the third link: 1.7 x 10^-10 kg/km3. which is, if I'm correct, 1.7 x 10^-25 kg/cm3; and given the mass of a proton as 1.67262158 x 10^-27 kg, this is around a hundred protons/cm3 in average, compared to (google-google) 7 protons/cm3 on our solar wind. Stormy weather!

    However, the figure given for the expansion speed of the nebula, 20 km/s, is way lower than the 300-900 km/s of the solar wind. Please correct me where I'm wrong.
  5. Dec 26, 2007 #4


    User Avatar
    Staff Emeritus
    Science Advisor

    Yes the 20 km/s is quite low compared to solar wind velocities.

    Solar Wind Data




    http://www.dxlc.com/solar/solwind.html [Broken]

    Don't know if this will help, but it might have some useful numbers or references.

    Material Enhancement In Protoplanetary Nebulae By Particle Drift
    Through Evaporation Fronts
    http://www.journals.uchicago.edu/doi/pdf/10.1086/423611 [Broken]

    See - http://www.physics.hku.hk/~nature/CD/regular_e/lectures/chap13.html [Broken] (bottom of page)
    In most region of space, the particle density is about 1 atom per cubic centimeter, however, in some region of space, the density is over 1000 atom/cm3. (This is about the best vacuum made by human, while the density of air is about 1019 atom/cm3.) These regions are called nebulae. The typical size of a nebula is about hundred light years. Nebulae are made up of gases and dusts. An example is M42 in Orion.

    Lecture 9 : HII regions and planetary nebulae

    On the Reliability of Planetary Nebulae as Extragalactic Probes

    I saw a number for IDP, but I'm not sure if it's relevant to nebulae.
    Last edited by a moderator: May 3, 2017
  6. Dec 26, 2007 #5
    The nebula would not affect vision significantly over AU scales. Over light year scales, yes. The presentation of nebula in scifi is entirely unrealistic.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook