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  2. Planetary nebula - Wikipedia

    en.wikipedia.org/wiki/Planetary_nebula

    A typical planetary nebula is roughly one light year across, and consists of extremely rarefied gas, with a density generally from 100 to 10,000 particles per cm 3. [42] (The Earth's atmosphere, by comparison, contains 2.5 × 10 19 particles per cm 3.) Young planetary nebulae have the highest densities, sometimes as high as 10 6 particles per ...

  3. Asymptotic giant branch - Wikipedia

    en.wikipedia.org/wiki/Asymptotic_giant_branch

    Formation of a planetary nebula at the end of the asymptotic giant branch phase. The extensive mass loss of AGB stars means that they are surrounded by an extended circumstellar envelope (CSE). Given a mean AGB lifetime of one Myr and an outer velocity of 10 km/s, its maximum radius can be estimated to be roughly 3 × 10 14 km (30 light years).

  4. Hertzsprung–Russell diagram - Wikipedia

    en.wikipedia.org/wiki/Hertzsprung–Russell_diagram

    This type of diagram could be called temperature-luminosity diagram, but this term is hardly ever used; when the distinction is made, this form is called the theoretical Hertzsprung–Russell diagram instead. A peculiar characteristic of this form of the H–R diagram is that the temperatures are plotted from high temperature to low temperature ...

  5. List of planetary nebulae - Wikipedia

    en.wikipedia.org/wiki/List_of_planetary_nebulae

    Cat's Eye Nebula: NGC 6543: 1786 3.3 ± 0.9 9.8B Draco: Little Ghost Nebula: NGC 6369: 1800 (prior to) 2 ± 3 9.9 Ophiuchus: Medusa Nebula: Abell 21 1955 1.0 (approx.) 15.99 Gemini: Jewel Bug Nebula: NGC 7027: 1878 3.0 (approx.) 10 Cygnus: Helix Nebula: NGC 7293: 1824 0.68 +0.15 −0.08: 7.6 Aquarius: Little Dumbbell Nebula: M76: NGC 650, NGC ...

  6. IC 418 - Wikipedia

    en.wikipedia.org/wiki/IC_418

    IC 418, also known as the Spirograph Nebula, is a planetary nebula located in the constellation of Lepus about 3,600 ly away from Earth.It spans 0.3 light-years across. The central star of the planetary nebula, HD 35914, is an O-type star with a spectral type of O7fp. [4]

  7. Helix Nebula - Wikipedia

    en.wikipedia.org/wiki/Helix_nebula

    The Helix Nebula (also known as NGC 7293 or Caldwell 63) is a planetary nebula (PN) located in the constellation Aquarius. Discovered by Karl Ludwig Harding, most likely before 1824, this object is one of the closest of all the bright planetary nebulae to Earth. [3] The distance, measured by the Gaia mission, is 655±13 light-years. [4]

  8. Red-giant branch - Wikipedia

    en.wikipedia.org/wiki/Red-giant_branch

    The term red-giant branch came into use during the 1940s and 1950s, although initially just as a general term to refer to the red-giant region of the Hertzsprung–Russell diagram. Although the basis of a thermonuclear main-sequence lifetime, followed by a thermodynamic contraction phase to a white dwarf was understood by 1940, the internal ...

  9. NGC 2818 - Wikipedia

    en.wikipedia.org/wiki/NGC_2818

    NGC 2818 is a planetary nebula located in the southern constellation Pyxis (The Compass). It consists largely of glowing gases from the star's outer layers ejected during the final stages of its life when it had run out of the fuel necessary to sustain its core fusion processes.