The Eskimo Nebula - A View from the Arid Lands
The Eskimo Nebula - A View from the Arid Lands
By Way of Introduction
In a manner of speaking, we are born out of the earth, walk on it for a while and finally become part of it when we die and so too with a star. It is born out of the cosmos, wanders it for a while and finally becomes a part of it when it dies. In this way, both a star's existence, like a human life, is a rite of death, a being-towards a something else; a transformation.
The physical recycling of life serves as a reminder of our own ultimate fate and likewise that of the Sun; for the star that was once the Eskimo Nebula is a good illustration of what the Sun’s own passing away will be like as it ejects its matter into space, forming giant gas and dust clouds which may condense with other interstellar material into planets and stars, comets and meteorites and organic life.
The Eskimo Nebula or NGC 2392
The Eskimo Nebula or NGC 2392 was a sun much like our own, a typical main sequence star chugging along in a steady state of nuclear fusion, transforming 700 million tons of hydrogen into helium every second for billions of years. Then about 10,000 years ago - as the ice-age was coming to an end - the hydrogen supply in the star’s core ran out. Nuclear fusion ground to a halt and through the force of gravity, the helium core collapsed creating temperatures high enough to trigger the fusion of helium into carbon and oxygen.
Far from the burning core, on the outer hydrogen layers, the star was expanding into a red giant, a colossal stellar object with a diameter of at least 2 AU. Once the helium fusion ended, the core collapsed again, but now there was not enough energy to spark further nuclear reactions or to counter the force of gravity and so the star collapsed until it was about the size of Earth and became a white dwarf.
The Eskimo’s white dwarf is a relatively small object in terms of volume but it packs a lot of mass. It is probably about the size of Earth but with a mass equal to that of the Sun. Surrounding this stellar remnant is a shell composed of expanding helium and hydrogen gases whose electrons are excited by ultraviolet radiation emitting from the white dwarf in the form of stellar winds.
The excited gas is visible as a planetary nebula, detected in a small telescope as a bright, ghostly cloud whilst with deep exposure you can witness one of the most captivating and intrinsically beautiful objects found in the natural world.
Not only is the Eskimo Nebula aesthetically gorgeous but as with all things which must come to pass and die, it too contains the building blocks of life. Spectroscopy has detected four primary elements within it, namely, hydrogen (green), helium (violet), nitrogen (red), and oxygen (blue). Indeed, the nebula’s name derives from these gases which light up as a ‘hood’ surrounding a ‘face’ made up of two elliptical lobes. No doubt, the snub that is the nose is the small central star.
The Eskimo Nebula is estimated to be anything from 2,870 to 5,000 light years from Earth, has a diameter of about half a light year and the gas we see probably left the small central white dwarf some 1,500 years ago. If this is so, NGC 2392 is one of the youngest planetary nebula known.
A Sketch & Observation
The planteary nebula lies in the constellation of Gemini and even with the small 4” refractor, it was clearly visible and held up well to magnification. As can be seen from the sketch, there was a brighter central region surrounded by a fainter halo of nebulosity and although the inner circle hinted at more detail, due to average seeing conditions and probably being at the refractor’s Dawes limit, the tiny white dwarf at approximately magnitude 10.5 was not seen.
However, this was not important. That bitter evening this sketch was made the Eskimo Nebula shone forth as a comforting metaphor. The original sun - which had been so much like our own - was now long gone but it did not sleep, it had not died. It was just something else.
Equipment used for the observation was a Tal 100rs, an 18mm X-Cel LX mounted on an AZ 4. The sketch was drawn the 12th of November, a cold night using a 4B, 2B and B pencil for the stars and a blending stub for the nebula.
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