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Hubble's Variable Nebula
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Image captured with a 100mm f5 Helios achromatic refractor and Canon EOS 350. 

Picture 852



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L

Posts: 129605
Date:
NGC 2261
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NGC 2261 (also known as Hubble's Variable Nebula, Caldwell 46 or LBN 920) is a magnitude 9.0 emission and reflection nebula located 272 light years away in the constellation Monoceros.
The nebula is illuminated by the T Tauri star R Monocerotis. Because the star is variable, (varying between 10.0 and 12.0, with an average apparent magnitude of about 10.37), it also changes the magnitude of the nebula.

NGC 2261 is located just beside, and linked to, the famous Cone Nebula. Although quite small, it should be visible in even small amateur telescopes due to its compactness. The variations in brightness of the nebula are appreciably over the course of a few months. Strangely, The variations in the nebula do not follow the variability cycle of the star, R Monocerotis.
Astronomer Carl Otto Lampland was one of the first to carry out a photographic survey on this unusual phenomenon; he suggested it may be due to a rotating dark nebula obscuring the object.  In 1959, George Herbig noted that the central star was actually a brilliant and tiny triangular-shaped nebula, which in turn contained a newly formed star. It is thought that this type of protoplanetary disk structure also existed four billion years ago around our Sun, during the formation of the planets.
The central star of the nebula is actually a double star system comprising two components, the brightest of which is about 10 times larger than the Sun, but due to the dense nebulosity their light is not observable in the range of visible light, but only in the infrared. The system is therefore probably composed of two T Tauri or Herbig Ae stars, that formed about 300,000 years ago. The distance between the two components is about 500 AU.
The variability of the nebula is now thought to be caused by filaments of gas are expelled from the protoplanetary disk in a double-cone shape, and which follow the lines of the magnetic field of the stars, thus causing changes observable.

The best time to observe this object is in the evenings between December and May, and thanks to its location not far from the celestial equator, it is equally observable from both hemispheres.

The German-British astronomer William Herschel at Datchet, Berkshire, discovered the celestial object on December 26 1783. 

NGC 2261 was imaged as Palomar Observatory's Hale Telescope's first light by Edwin Hubble on January 26, 1949

Right Ascension 06h 39m 09.5s, Declination +08° 44' 39"

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