|
|
|
Last update 23/04/2007 Most images on this web site can be clicked on to be enlarged Globular Cluster (GC) Globular clusters are spherical bodies made up of hundreds of thousands to millions of older stars and have diameters of 100 to 300 light years. They orbit in a halo around our galaxy. About 140 such clusters orbit our galaxy the Milky Way.
Nebular (N) This is the term used for clouds of dust and gas, which float in space. There are various types classified by the way they give off their light: Emission nebulae which emit their own light, reflection nebulae which reflect light from nearby stars and dark nebulae which appear dark on a brighter background. These clouds are normally the birthplace of stars and planets, the nurseries of interstellar space.
The best known diffuse
nebula and one of the nearest regions to the Sun in which stars are
presently being formed. It is visible to the naked eye south of Orion's
Belt as a fuzzy patch known as Orion's
Sword.
Orion M42 SAC10 ED 80 Williams Optics (1.5hr)
Planetary
Nebular (PN) Planetary nebulae are the remnants of red giants that have shed their outer layers as a cloud of gas surrounding the original star. The central, highly evolved, star emits very high levels of radiation, ionizing the gas and causing it to glow. These objects are around half a light-year in diameter and last for about 100 000 years, after which they disperse into interstellar space and disappear, leaving behind the remnants of the star, now a white dwarf. Planetary nebulae take many shapes; some are perfect rings as in The Ring Nebula (M57) in Lyra and others are more irregular as in The Dumbbell Nebular (M27) in Vulpecula.
Galaxy
(Gal)
A galaxy is a collection of stars, gas, clusters
and nebulae, in fact, all of the objects in this chapter. They are the largest
single component in our universe. They may be isolated or in small groups, as
ours, called the Local Group, or in larger groups as in the Virgo Cluster. Size
and shape also varies greatly, galaxies can range from a dwarf, with less than a
million stars to giants with more than a million million stars. Diameters can
range from a few hundred to over 600 000 light years across. Their shape also varies, they fall under
two main categories, elliptical, having smooth centralized distribution of stars
and spirals which are split into three groups, spirals, bared galaxies that
have discs and spirals, lenticular galaxies that have a disc but no spirals.
A spiral galaxy (type Sb or Sc) in Canes Venatici that appears to lie in the M51 Group dominated by the Whirlpool Galaxy (M51); it was discovered in 1779 by Pierre Méchain. The Sunflower's spiral arms show up as a grainy background, which brightens slowly at first, going in from the periphery, but then rapidly to the nuclear region. It hosted a Type I supernova (1971I), first seen on May 25, 1971, which reached magnitude 11.8.
Open Cluster with Nebulosity (OCN) The same as open clusters, but with the presence of nebulosity. A good example of this is The Pleiades (M45) in Taurus.
Open Cluster (OC) Open clusters are irregular groups ranging from ten to several hundred stars, which formed in the spiral arms of our galaxy. They are normally about 50 light years across and are made up of young stars. There age’s range from a few million to several billion years old, some are still so young that traces of the nebular from which they formed still exists as fine mist surrounding the stars. Good examples are the Double Clusters in Perseus (NGC 869) and the Beehive Cluster (M44) in Cancer. Footnote :
References
and links from: The Encyclopedia of Astrobiology, Astronomy, and Space
flight
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
