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RE: NGC 2440
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The planetary nebula NGC 2440 was discovered by the German-British astronomer William Herschel using a 47.5 cm (18.7 inch) f/13 speculum reflector on the 4th March 1790.

Right Ascension 07h 41m 54.9s, Declination 18 12 29.7"

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HD62166
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The central stars of planetary nebulae are the hottest known stars. They have been detected with surface temperatures up to 250,000 K.
HD62166, the white dwarf star at the center of the NGC 2440 planetary nebula has been measured at greater than 200,000 degrees Celsius - which is more than 30 times hotter and 250 times brighter than the Sun.
The nebula is situated in the constellation Puppis.

Astronomers use a star's light to determine the star's temperature, composition and motion. Astronomers analyse a star's light by looking at it's intensity at different wavelengths. Also known as Wien's displacement law (developed by German physicist Wilhelm Wien) links the wavelength at which the most energy is given out by an object and its temperature. Astronomers put filters of different standard colours on telescope to allow only light of a particular colour from a star to pass. In this way, astronomers determine the brightness of a star at particular wavelengths. From this information, astronomers can use Wien's law to determine the star's surface temperature.
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NGC 2440
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This image, taken by NASA's Hubble Space Telescope, shows the colourful "last hurrah" of a star like our Sun. The star is ending its life by casting off its outer layers of gas, which formed a cocoon around the star's remaining core. Ultraviolet light from the dying star makes the material glow. The burned-out star, called a white dwarf, is the white dot in the centre. Our Sun will eventually burn out and shroud itself with stellar debris, but not for another 5 billion years.

NGC 2440
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Credit: NASA

Position (J2000): R.A. 07h 41m 55.3s Dec. -18 12' 31"

Our Milky Way Galaxy is littered with these stellar relics, called planetary nebulae. The objects have nothing to do with planets. Eighteenth- and nineteenth-century astronomers named them planetary nebulae because through small telescopes they resembled the disks of the distant planets Uranus and Neptune. The planetary nebula in this image is called NGC 2440.
The white dwarf at the centre of NGC 2440 is one of the hottest known, with a surface temperature of nearly 400,000 degrees Fahrenheit (200,000 degrees Celsius). The nebula's chaotic structure suggests that the star shed its mass episodically. During each outburst, the star expelled material in a different direction. This can be seen in the two bow tie-shaped lobes. The nebula also is rich in clouds of dust, some of which form long, dark streaks pointing away from the star. NGC 2440 lies about 4,000 light-years from Earth in the direction of the constellation Puppis.
The image was taken Feb. 6, 2007, with Hubble's Wide Field Planetary Camera 2. The colours correspond to material expelled by the star. Blue corresponds to helium; blue-green to oxygen; and red to nitrogen and hydrogen.

Source: Space Telescope Science Institute

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