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NGC 6572: A Dazzling Planetary Nebula
ESA Hubble | Picture of the Week | 13 Dec 2010
The NASA/ESA Hubble Space Telescope has turned its eagle eye to the planetary nebula NGC 6572, a very bright example of these strange but beautiful objects. Planetary nebulae are created during the late stages of the evolution of certain stars that eject gas into space and emit intense ultraviolet radiation that makes the material glow. This picture of NGC 6572 shows the intricate shapes that can develop as stars exhale their last breaths. Hubble has even imaged the central white dwarf star, the origin of the dazzling nebula, but now a faint, but hot, vestige of its former glory.
NGC 6572 only began to shed its gases a few thousand years ago, so it is a fairly young planetary nebula. As a result the material is still quite concentrated, which explains why it is abnormally bright. The envelope of gas is currently racing out into space at a speed of around 15 kilometres every second and as it becomes more diffuse, it will dim.
NGC 6572 was discovered in 1825 by the German astronomer Friedrich Georg Wilhelm von Struve, who came from a family of distinguished stargazers. The name planetary nebula is left over from the time when the telescopes of early astronomers were not good enough to reveal the true nature of these objects. To many, the discs looked like the outer planets Uranus and Neptune. The application of spectral analysis, later in the 19th century, first revealed that they were glowing gas clouds.
NGC 6572 is magnitude 8.1, easily bright enough to make it an appealing target for amateur astronomers with telescopes. It is located within the large constellation of Ophiuchus (the Serpent Bearer) and at low magnification it will appear to be just a coloured star, but higher magnification will reveal its shape. Some observers report that NGC 6572 looks blue, while others state that it is green. Colour as seen through the eyepiece is often a matter of interpretation, so you may make your own decision!
This picture was created from images taken with Hubble’s Wide Field Camera 2. Images through a blue filter that isolates the glow from hydrogen gas (Hβ, F487N, coloured dark blue), a green filter that isolates emission from ionised oxygen (F502N, coloured blue), a yellow broadband filter (F555W, coloured green) and a red filter that passes emission from hydrogen (Hα, F656N) have been combined. The exposure times were 360 s, 240 s, 100 s and 180 s, respectively and the field of view is just 29 arcseconds across.
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NGC 6572 was discovered in 1825 by the German astronomer Friedrich Georg Wilhelm von Struve, who came from a family of distinguished stargazers.
Strive, v. i. [imp. Strove; p. p. Striven (Rarely, Strove)] [OF. estriver; of Teutonic origin, and akin to G. streben, D. streven, Dan. stræbe, Sw. sträfva. Cf. Strife.] To make efforts; to use exertions; to endeavor with earnestness; to labor hard.
Clear day at Pulkovo Observatory in 1839
<<Friedrich Georg Wilhelm von Struve (Russian: Vasily Yakovlevich Struve) (April 15, 1793 – November 23, 1864) was a Baltic-German astronomer from a famous dynasty of astronomers. He was born at Altona, Germany, the son of Jacob Struve (1755–1841), and was the second of an entire family of astronomers through five generations. He was the great-grandfather of Otto Struve and the father of Otto Wilhelm von Struve. He was also the grandfather of Hermann Struve, who was Otto Struve's uncle. Struve's father Jacob moved the family from French-occupied Germany to Livonia in Imperial Russia to avoid military service. In 1815 Friedrich married Emilie Wall (1796–1834) in Altona, who bore 12 children. After Emilie died, he remarried to Johanna Henriette Francisca Bartels (1807–1867), a daughter of the mathematician Martin Bartels (the tutor of Gauss in Brunswick and the educator of Lobachevsky at the University of Kazan), who bore him six more children
In 1808 he entered the University of Tartu in Estonia, where he first studied philology (i.e., the study of language in written historical sources), but soon turned his attention to astronomy. From 1813 to 1820, he taught at the university and observed at Dorpat Observatory (i.e., the largest astronomical observatory in Estonia located on Tõravere hill in Nõo Parish, Tartu
Friedrich Georg Wilhelm von Struve remained at Tartu, occupied with research on double stars and geodesy until 1839, when he founded and became director of the new Pulkovo Observatory near St Petersburg. Among other honors, he won the Gold Medal of the Royal Astronomical Society in 1826, and was elected a member of the Royal Swedish Academy of Sciences in 1833.
The asteroid 768 Struveana was named jointly in his honour and that of Otto Wilhelm and Karl Hermann Struve and a lunar crater was named for another 3 astronomers of the Struve family: Friedrich Georg Wilhelm, Otto Wilhelm and Otto.
Struve's discovered a very large number of double stars and in 1827 published his double star catalogue Catalogus novus stellarum duplicium. Struve made micrometric measurements of 2714 double stars from 1824 to 1837 and published these in his work Stellarum duplicium et multiplicium mensurae micrometricae. Struve carefully measured the "constant of aberration" in 1843. He was also the first to measure the parallax of Vega, although Friedrich Bessel had been the first to measure the parallax of a star (61 Cygni). In an 1847 work, Etudes d'Astronomie Stellaire: Sur la voie lactee et sur la distance des etoiles fixes, Struve was one of the first astronomers to identify the effects of interstellar extinction. His estimate of the average rate of visual extinction, 1 mag per kpc, is remarkably close to modern estimates (0.7-1.0 mag per kpc).>>