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Submitted: Mon, 2014-03-17 21:34

M 82

Messier 82 (also known as NGC 3034, Cigar Galaxy or M82) is a starburst galaxy about 12 million light-years away in the constellation Ursa Major and a member of the M81 Group. It is about five times more luminous than the whole Milky Way and has a center one hundred times more luminous than our galaxy's center. The starburst activity is thought to have been triggered by interaction with neighboring galaxy M81. As the closest starburst galaxy to our own, M82 is the prototypical example of this galaxy type. SN 2014J, a type Ia supernova, was discovered in the galaxy on 21 January 2014. In 2014, in studying M82, scientists discovered the brightest pulsar yet known, designated M82 X-2.
M82 was previously believed to be an irregular galaxy. In 2005, however, two symmetric spiral arms were discovered in near-infrared (NIR) images of M82. The arms were detected by subtracting an axisymmetric exponential disk from the NIR images. Even though the arms were detected in NIR images, they are bluer than the disk. The arms were previously missed due to M82's high disk surface brightness, our nearly edge-on view of this galaxy (~80°), and obscuration by a complex network of dusty filaments in its optical images. These arms emanate from the ends of the NIR bar and can be followed for the length of 3 disc scales. Assuming that the northern part of M82 is nearer to us, as most of the literature does, the observed sense of rotation implies trailing arms.

M 82
Submitted: Fri, 2014-02-28 10:48

IC 434

IC 434 is a bright emission nebula in the constellation Orion. It was discovered on February 1, 1786 by William Herschel. The Horsehead Nebula is a dark nebula silhouetted against it.

The Horsehead Nebula is one of the most recognizable of deep sky objects by virtue of its distinct resemblance to its namesake. It is certainly the best known example of a dark nebula. The Horsehead is also known by the less descriptive Barnard 33. The nebula is a classic dark nebula and may only be seen because it is silhouetted against the very faint glow of IC 434, a reef of tenuous emission nebulosity.

Burnhams Celestial Handbook reports that the Horsehead was first detected in photographs in 1889 by E. Pickering. Burnhams also reports that the significance of this object was not immediately recognized. Early descriptions refer to this object as a "bay" or a gap in IC 434. It appears that E. Barnard was the first to recognize that it was actually obscuring light from behind.

The Horsehead is believed to a dense cloud of tiny interstellar grains of dust that blocks the light of the emission nebula IC 434 and stars behind. While dark nebula are generally invisible (except of course where back lit as in the case of the Horsehead), their dust grains very effectively absorb light and ultraviolet radiation and then re-radiate this energy at infrared wavelengths.

The Horsehead nebula is one of the most difficult of visual objects and requires dark skies and large aperture to view.

IC 434