Astronomy Picture of the Day

Discover the cosmos! Each day we feature a different image or photograph of our fascinating universe, along with a brief explanation written by a professional astronomer.

January 18, 1996
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MyCn18: An Hourglass Nebula
Credit: R. Sahai and J. Trauger (JPL), WFPC2 Science Team, NASA,

Explanation: The sands of time are running out for the central star of this hourglass-shaped planetary nebula. With its nuclear fuel exhausted, this brief, spectacular, closing phase of a Sun-like star's life occurs as its outer layers are ejected - its core becoming a cooling, fading White Dwarf. Astronomers have recently used the Hubble Space Telescope (HST) to make a series of images of planetary nebulae, including the one above. Here, delicate rings of colorful glowing gas (nitrogen-red, hydrogen-green, and oxygen-blue) outline the tenuous walls of the "hourglass". The unprecedented sharpness of the HST images has revealed surprising details of the nebula ejection process and may help resolve the outstanding mystery of the variety of complex shapes and symmetries of planetary nebulae.

Tomorrow's picture: The Dusty Disk of Beta Pic

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Authors & editors: Robert Nemiroff (GMU) & Jerry Bonnell (USRA).
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