Astronomy Benalla  General Meeting Presentations - Wednesday 16th June 2010

Reports - 2010

Pictures from the Hubble Site

Constellation of the Month.      Presenter: Patrick Watson The largest constellation of them all, representing a water snake (serpent). Hydra meanders from north of the celestial equator, into the southern celestial hemisphere and is over 100⁰ (degrees of arc) long. In Greek mythology, Hercules was required to slay Hydra as one of his twelve labours. Hydra can hardly be called prominent. Its faint stars make it difficult to trace the snake’s winding path across the sky, south of the constellations Libra, Virgo, Corvus, Crater, Sextans, Leo and Cancer. The most distinctive part is the snake’s head marked with a trapezoid of stars. The following notable objects were shown and discussed: • Open cluster M48 (NGC 2548). Over a dozen of this cluster’s 80 stars may be seen through 7x and larger binoculars • Planetary nebula NGC 3242 - ‘GHOST OF JUPITER’. An 8^th magnitude blue disk seen in 7 x 50 binoculars.  Large telescopes and photographs show a strong resemblance to a human eye, with a fainter outer shell of gas surrounding the brighter core. The central star is 11^th magnitude. • Globular star cluster M68 (NGC 4590). Modern estimates place M68 at just over 30,000 light years away and approaching us at about 117 kilometers per second. This rich globular cluster contains over 100,000 stars. M68 It is about 100,000 light-years in diameter. • The variable red giant star R Hydrae. The image shown is from the Spitzer Space Telescope and showed the "bow shock" of this dying star. Bow shocks are formed where the stellar wind (travelling at relative rates greater than the local speed of sound) from a star are pushed into a bow shape as the star plunges through the gas and dust between stars (similar to a ships bow-wave; an aircraft sonic boom) . Our own Sun has a bow shock, but prior to this image one had never been observed around this particular class of red giant star. R Hya moves through space at approximately 50 kilometers per second. As it does so, it discharges dust and gas into space. Because the star is relatively cool, that ejecta quickly assumes a solid state and collides with the interstellar medium. The resulting dusty nebula is invisible to the naked eye but can be detected using an infrared telescope. The bow shock displayed is 16,295 AU from the star to the apex and 6,188 AU thick. The mass of the bow shock is about 400 times the mass of the Earth. Since its discovery in 1704, its period has shortened from 500 days to the present 390 • Variable carbon star V Hydrae is one of the reddest stars visible. A carbon star is a late type giant star similar to a red giant (or occasionally to a red dwarf) whose atmosphere contains more carbon than oxygen; the two elements combine in the upper layers of the star, forming carbon monoxide, which consumes all the oxygen in the atmosphere, leaving carbon atoms free to form other carbon compounds, giving the star a "sooty" atmosphere and a strikingly red appearance. Varies from m_v 7.0 – 11.5 • Spiral galaxy M83 (NGC 5236). Discovered in 1752 by Lacaille.  Carries an Hubble Classification of Sc.