Everything Science Forum

Moon and Antares - June 19, 2005 - from Stardate.org (http://stardate.org/radio/program.php?f=today)

The heart of Scorpius lines up near the almost-full Moon tonight: the bright orange star Antares. It's to the lower left of the Moon at nightfall, and the Moon will move closer to the star during the night.

Scorpius is one of the most prominent constellations. In addition to Antares, it boasts an array of bright blue stars that give the constellation its distinctive hook shape. Yet it's only because of an odd twist in the Milky Way that many people at mid-northern latitudes can see the scorpion.

Most of the bright stars like those in Scorpius outline the Milky Way, the ghostly band of light that represents our edge-on view of the galaxy. But the stars of Scorpius hover far north of this band.

That's because Antares and many of the other bright stars of Scorpius belong to a vast belt of stars that surrounds the Sun. It's called Gould's Belt, for an American astronomer who noticed it during a journey to Argentina. No one knows what created Gould's Belt, but it's thousands of light-years across, and it's tilted about 20 degrees to the plane of the galaxy.

Because the bright stars of Scorpius belong to Gould's Belt, they rise far north of the Milky Way. That puts them clear of the southern horizon for stargazers across the United States.

Look for the stars of Scorpius near the Moon the next couple of nights. The Moon will move below Antares by tomorrow night, so it'll stand near the middle of this beautiful constellation.

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Gould's Belt is a ring of luminous B-type stars tilted by about 20 degrees with respect to the galactic plane at the location of the sun, and roughly centered on the sun's position in the Milky Way. We don't really know how it was formed, but the massive stars it contains out to the distance of the Orion Nebula are only a few 10s of million of years old, so it is a relatively young 'structure'.

It was discovered in 1879 by the astronomer B. A. Gould who was then the director of the Cordoba Observatory in Argentina. He discovered it by studying the distribution in space of the nearest luminous stars. It has since been detected, as well, in the distribution of the nearest dark nebulae by Beverly Lynds at the National Radio Astronomy Observatory in the 1960's.

  from Ask the Astronomer (http://www.astronomycafe.net/)

Gould’s Belt (Part I) (http://ottawa.rasc.ca/observers/1999/an9912p8.html) and (Part II) (http://ottawa.rasc.ca/observers/2000/an0001p3.html) - Glenn LeDrew

Recent analyses have shown that if the sources of cosmic-rays are discrete, as are supernova remnants, then the spectra of cosmic-ray electrons vary greatly with location and time and the locally measured electron spectrum may be not representative of the electron spectra elsewhere in the Galaxy. We have continued the earlier studies by investigating the impact of the star forming region Gould's Belt on the local electron spectrum at GeV to TeV energies. Our results indicate that if the electron sources in Gould's Belt are continous, the local electron spectrum would be slightly hardened with a spectral index increase of  due to the higher SN rate in the Belt. If the electron sources are discrete, which is the more probable case, the local electron spectrum above ~30 GeV is variable with similar amplitude as without Gould's Belt. By the method of Monte Carlo, we have also studied the correlation of the local electron flux with that in nearby molecular cloud complexes. The high energy electron flux above 30 GeV near the Orion, Monoceros, Cassiopeia, Cepheus, and Perseus clouds does not vary in coordination with the local flux, but a correlation between the electron flux in the Taurus and Ophiuchus clouds and that in solar vicinity is indicated by our study, implying that the spatial correlation length is of the order of 200 pc at electron energies of 100 GeV and higher. This would permit hard -ray spectra from inverse Compton scattering to be produced in the more distant clouds, in agreement with the GeV excess observed towards Orion and Monoceros, without affecting the emissivity spectra of the very nearby clouds as in Taurus and Ophiuchus.

from The imprint of Gould's Belt on the local cosmic-ray electron spectrum (abstract) (http://www.edpsciences.org/articles/aa/abs/2003/38/aa2695/aa2695.html)