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Planetary Nebulae, Stars and a Comet



Most pics courtesy of NASA






NGC 2346:  A Butterfly-Shaped Planetary Nebula




Credit:  Massimo Stiavelli (STScI), Inge Heyer (STScI) et al.,
& the Hubble Heritage Team (AURA/ STScI/ NASA)

           Explanation:  It may look like a butterfly, but it's bigger than our Solar System.  NGC 2346 is a planetary nebula made of gas and dust that has evolved into a familiar shape.  At the heart of the bipolar planetary nebula is a pair of close stars orbiting each other once every sixteen days.  The tale of how the butterfly blossomed probably began millions of years ago, when the stars were farther apart.  The more massive star expanded to encompass its binary companion, causing the two to spiral closer and expel rings of gas.  Later, bubbles of hot gas emerged as the core of the massive red giant star became uncovered.  In billions of years, our Sun will become a red giant and emit a planetary nebula - but probably not in the shape of a butterfly, because the Sun has no binary star companion.




Halloween and the Ghost Head Nebula




Credit:  Mohammad Heydari-Malayeri (Observatoire de Paris) et al., ESA, NASA

           Explanation:  Halloween's origin is ancient and astronomical.  Since the fifth century BC, Halloween has been celebrated as a cross-quarter day, a day halfway between an equinox (equal day / equal night) and a solstice (minimum day / maximum night in the northern hemisphere).  With our modern calendar, however, the real cross-quarter day will occur next week.  Another cross-quarter day is Groundhog's Day.  Halloween's modern celebration retains historic roots in dressing to scare away the spirits of the dead.  A perhaps-fitting modern tribute to this ancient holiday is the above-pictured Ghost Head Nebula taken with the Hubble Space Telescope.  Appearing similar to the icon of a fictional ghost, NGC 2080 is actually a star forming region in the Large Magellanic Cloud, a satellite galaxy of our own Milky Way Galaxy.  The Ghost Head Nebula spans about 50 light-years and is shown in representative colors.




VDB 142 in Cepheus




Credit:  Arne Henden (US Naval Observatory, Flagstaff)
Image Processed by Al Kelly

           Explanation:  A gorgeous collection of dust and gas nebulae in the Northern Milky Way graces the high and far off constellation of Cepheus.  With colors based on astronomical filters, this close up of the region highlights stars embedded in curiously shaped cosmic clouds.  Near the central faint (9th magnitude) star in the image, dust clouds reflect the starlight, creating a bluish reflection nebula cataloged in 1966 as VDB 142.  The area's bright reddish emission nebulae indicate the prescence of clouds of atomic hydrogen gas.  Stripped of electrons by invisible ultraviolet light, the hydrogen atoms emit their characteristic visible red light as electrons and atoms recombine.  Sweptback clouds of obscuring dust, dark nebulae, are silhouetted against the bright background.  Representing the stuff stars are made of, all these nebulae lie within the large young star cluster complex IC 1396, 3,000 light years from Earth.




IC 418:  The Spirograph Nebula




Credit:  R. Sahai (JPL) et al., Hubble Heritage Team (STScI/AURA), NASA

           Explanation:  What is creating the strange texture of IC 418?  Dubbed the Spirograph Nebula for its resemblance to drawings from a cyclical drawing tool, planetary nebula IC 418 shows patterns that are not well understood.  Perhaps they are related to chaotic winds from the variable central star, which changes brightness unpredictably in just a few hours.  By contrast, evidence indicates that only a few million years ago, IC 418 was probably a well-understood star similar to our Sun.  Only a few thousand years ago, IC 418 was probably a common red giant star.  Since running out of nuclear fuel, though, the outer envelope has begun expanding outward leaving a hot remnant core destined to become a white-dwarf star, visible in the image center.  The light from the central core excites surrounding atoms in the nebula causing them to glow.  IC 418 lies about 2000 light-years away and spans 0.3 light-years across.  This recently released false-color image taken from the Hubble Space Telescope reveals the unusual details.




Hen 1357:  New Born Nebula




Credit:  M. Bobrowsky, NASA

           Explanation:  This Hubble Space Telescope snapshot shows Hen-1357, the youngest known planetary nebula.  Graceful, gentle curves and symmetry suggest its popular name - The Stingray Nebula.  Observations in the 1970s detected no nebular material, but this image from March 1996 clearly shows the Stingray's emerging bubbles and rings of shocked and ionized gas.  The gas is energized by the hot central star as it nears the end of its life, evolving toward a final white dwarf phase.  The image also shows a companion star (at about 10 o'clock) within the nebula.  Astronomers suspect that such companions account for the complex shapes and rings of this and many other planetary nebulae.  This cosmic infant is about 130 times the size of our own solar system and growing.  It is 18,000 light-years distant, in the southern constellation Ara.




Moon AND Stars




Composite Image Credit:  T.A. Rector, I.P. Dell'Antonio, NOAO, AURA, NSF

           Explanation:  Here's something you don't see too often ... a detailed picture of the full Moon surrounded by a rich field of background stars.  It's true that bright moonlight scattered by the atmosphere tends to mask faint stars, but pictures of the sunlit portion of the Moon made with earthbound telescopes or even with cameras on the lunar surface often fail to show any background stars at all.  Why?  Because the exposure times are too short.  Very short exposures, lasting fractions of a second, are required to accurately record an image of the bright lunar surface.  But the background stars (and galaxies!), such as those visible above, are much fainter and need exposures lasting minutes to hours which would seriously overexpose the surface of the Moon.  So, of course this stunning view really is a combination of two digital images -- a short exposure, registering the exquisite lunar surface details at full Moon, superposed on a separate very long exposure, made with the Moon absent from the star field.  The final representation of Moon and background stars is very dramatic, even though it could not have been captured in a single exposure.




A Solar Prominence Erupts




Credit:  SOHO - EIT Consortium, ESA, NASA

           Explanation:  Our Sun is still very active.  Last year, our Sun went though Solar Maximum, the time in its 11-year cycle where the most sunspots and explosive activities occur.  Sunspots, the Solar Cycle, and solar prominences are all caused by the Sun's changing magnetic field.  Pictured above is a solar prominence that erupted on May 15, 2001, throwing electrons and ions out into the Solar System.  The image was taken in the ultraviolet light emitted by a specific type of ionized helium, a common element on the Sun.  Particularly hot areas appear in white, while relatively cool areas appear in red.  Our Sun should gradually quiet down until Solar Minimum occurs in 2007.




Comet Borrelly's Nucleus




Credit & Copyright: Deep Space 1 Team, JPL, NASA

           Explanation:  What does a comet nucleus look like?  To answer this question, NASA controllers drove an aging probe through the hostile environs of a distant comet, expecting that even if comet fragments disabled the spacecraft, it would be worth the risk.  The probe, Deep Space 1, survived.  Pictured above is the most detailed image ever taken of a comet nucleus, obtained Saturday by Deep Space 1 and released yesterday (9-25-01)by NASA.  Comet Borrelly's nucleus is seen to be about 8 kilometers long with mountains, faults, grooves, smooth rolling planes, and materials of vastly different reflectance.  Light colored regions are present near the center and seem to give rise to dust jets seen in Borrelly's coma, visible in distant images of the comet.  Previously, the best image of a comet nucleus came from the Giotto mission to Comet Halley in 1986.  Deep Space 1 images of Borrelly add welcomed bedrock to understanding Solar System history and to the accurate prediction of future brightness changes of notoriously fickle comets.




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