In dieser Ausgabe:

  • Sternstunde News
  • Dem Mond Phobos auf der Spur
  • Astrovorschau April

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NASA Breaking News
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All-sky map by IBEX satellite delivers major mystery: a "ribbon" in the heliosphere missed by the Voyagers
Dienstag, 20. Oktober 2009 um 00:00 Uhr
One year after its launch (see Update #320 header) the first sky maps by the Interstellar Boundary Explorer satellite have been published, showing the intensity of neutral atoms travelling from the heliosphere towards us. These maps reveal surprising and intense interactions between our home in the galaxy and interstellar space. What had been expected were small, gradual spatial variations at the interstellar boundary, some 15 billion km away. However, IBEX shows a very narrow ribbon that is two to three times brighter than anything else in the sky. The interstellar magnetic field probably plays a major role in creating this well-defined enhancement, but the physics are anything but understood. The IBEX principal investigator used the word "shocking" repeatedly during a NASA press conference - and said that at first they had thought the spacecraft was broken. But the measurements are confirmed, also by similar data collected by an instrument on the Cassini mission over the years.

The background: The solar wind of charged particles continuously travels at supersonic speeds away from the Sun in all directions, inflating a giant bubble in interstellar space called the heliosphere, i.e. the region of space dominated by the Sun's influence in which the Earth and other planets reside. As the solar wind travels outward, it sweeps up newly formed "pickup ions," which arise from the ionization of neutral particles drifting in from interstellar space. IBEX measures energetic neutral atoms (ENAs) traveling at speeds of roughly half a million to two and a half million miles per hour. These ENAs are produced from the solar wind and pick-up ions in the boundary region between the heliosphere and the local interstellar medium. IBEX has used two novel ENA cameras to image and map the heliosphere's global interaction. ENAs propagate in from all parts of the boundary and, by detecting their directions of arrival, IBEX builds up maps of this invisible region over a broad range of energies every six months.

While the Voyager spacecraft are providing pioneering point measurements of interactions in the interstellar boundary region at two locations, IBEX measurements demonstrate the importance of global observations: The bright narrow ribbon snakes through the sky just between the Voyager spacecraft, where it remained completely undetected until now. More time is needed to fully understand the IBEX data; however, because the ribbon appears to be ordered by the direction of the local interstellar magnetic field outside the heliosphere, IBEX observations suggest that the interstellar environment has far more influence on the structure of the heliosphere than anyone previously believed. A closer look at segments of the ribbon shows fine structures, which suggests that ion densities may be significantly enhanced in highly localized regions at the interstellar boundary.


You can find Daniel Fischers Cosmic Mirror here.

 

Paul Hombachs Astrovorschau

Im Mai müssen Sternfreunde mit einer sehr verkürzten Nacht vorlieb nehmen, zur Monatsmitte steht die Sonne (gerechnet für Bonn) zwischen 5:43 und 21:14 Uhr gut 15 1/2 Stunden über dem Horizont. Rechnet man die lange Dämmerung hinzu, so bleibt für die dunkle Nacht praktisch nur noch der Zeitraum zwischen Mitternacht und halb 3 Uhr am frühen Morgen. Gegen Monatsende beginnen für weite Teile Deutschlands die sogenannten weißen Nächte, während derer es im astronomischen Sinne überhaupt nicht mehr richtig dunkel wird. Am 14. Mai ist Neumond, aber in der zweiten Monatshälfte wird die Nacht zusätzlich vom Mond erhellt. Am 28.5. ist Vollmond, der in dieser Nacht sehr weit südlich nahe Antares im Sternbild Skorpion steht. Antares ist ein roter Riesenstern in 600 Lichtjahren Entfernung und leuchtet mindestens zehntausendfach heller als unser Zentralgestirn.
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