M8 - NGC6523
The irregular distribution of stars in this part of thr sky is due mainly to clouds of dust that dim the light of vast clouds of stars that make Sagittarius one of the brightest parts of the Milky Way. The Lagoon Nebula is an illuminated part of such a dark cloud and it reveals the dust as dark lines and globules silhouetted against the luminous gas. Within the nebula is the young star cluster NGC 6350. (Photograph by David Malin)
M20 - NGC6514
Measuring some forty light years across, the Trifid Nebula contains enough gas to make many thousands of stars. Within it a number of young hot stars have already formed. They cause the surrounding gas, mostly hydrogen, to emit its characteristic red light. However, one side of the nebula contains many dust grains that reflect the star's light, producing a bluish color. In some parts of the nebula the dust grains are so numerous that they hide the glowing gas ,producing three dark lanes, which give this beautiful object its name. (Photograph by David Malin)
M 4 - NGC 6121|
Dist. 6.800 l.y.
M4 is a globular cluster visible in dark skies about one degree west of the bright star Antares. M4 is perhaps the closest globular cluster at 6.800 light years, meaning that we see M4 only as it was 6.800 years ago, near the dawn of recorded human history. Although containing hundreds of thousands of stars and spanning over 50 light-years, M4 is one of the smallest and sparsest globular clusters known. A particularly unusual aspect for a globular cluster is M4's central bar of stars. M4 is one of the oldest objects for which astronomers can estimate age directly. Cluster white dwarfs appear to be at least nine billion years old - so ancient they limit the youth of our entire universe.
M 80 - NGC 6093
Magn. 7.2 - Dist. 27.100 l.y.
|The dusty region between Ophiucus and Scorpius contains some of the most colorful and spectacular nebulae ever photographed. The upper part of the picture is filled with the bluish glow of reflected light from hot stars near a huge, cool cloud of dust and gas where stars are born.|
|Dominating the lower half of ther picture is an over-exposed image of the red supergiant star Antares, a star that is steadily shedding material from its distended surface as it nears the end of its life. These solid particles reflect Antares' light and hide it in a nebula of its own making. Finally, partly surrounding Sigma Scorpii at the right of the picture is a red emission nebula, completing the most comprehensive collection of nebular types ever seen in one photograph. (by David Malin - Anglo-Australian Telescope).|
Dist. 5.900 l.y.
|M 7||M 6|
To some, the outline of the open cluster of stars M6 resembles a butterfly. Like other open clusters, M6 is composed predominantly of young blue stars, although the brightest star is nearly orange. M6 is estimated to be about 100 million years old. Determining the distance to clusters like M6 helps astronomers calibrate the distance scale of the universe.
|The Ring Nebula - M57|
Magn. 9.7 - Dist. 1960 l.y.
14.8 magn. central star
|The famous Ring Nebula M57 is often regarded as the prototype of a planetary nebula, and a showpiece in the northern hemisphere summer sky. Recent research has confirmed that it is, most probably, actually a ring (torus) of bright light-emitting material surrounding its central star, and not a spherical (or ellipsoidal) shell, thus coinciding with an early assumption by John Herschel. There are even indications that the overall shape might be more that of a cylinder viewed along the direction of the axis than that of a ring, i.e., we are looking down a tunnel of gas ejected by a star at the end of its nuclear-burning life.|
Color photos show that the material of the Ring is exposing a decreasing ionization level with increasing distance from the 100,000 to 120,000 K hot central star. The innermost region appears dark as it emits merely UV radiation, while in the inner visible ring, greenish forbidden light of ionized oxygene and nitrogene dominates the color, and in the outer region, only the red light of hydrogene can be excited.
The central star is a planet-sized white dwarf star, which shines at about 15th magnitude. Now over 100,000 K hot, it will soon start to cool down, shine as a white dwarf star for a while of several billions of years, and then eventually end as a cold Black Dwarf.
As for most planetary nebulae, the distance to the Ring Nebula M57 is not very wellknown. So, a good value for the distance still needs to be determined.
Magn. 5.0 - Dist. 880 l.y.
The North America Nebula
Magn. 7.0 - Dist. 2.300 l.y.
NGC6960 - The Veil Nebula
Filamentary, the Cygnus Loop
Magn. 8.0 - Dist. 2.600 l.y.
The large loop of gas was ejected about 30-40.000 years ago from a supernova, a star's final death throes. The loop is still expanding at a rate of 6 arc seconds every hundred years.
Sadr (Gamma Cygni) is the central star in Cygnus, the Swan, or Northern Cross, and is surrounded by nebulosity (IC 1318). In the bottom of the picture we see M29, open cluster (NGC6913) magn. 6.6, dist. 4.100 l.y., about 50 stars from 9th magnitude.
Other objects in the pictures are NGC6910, open cluster visible in both pictures, magn. 7.4, dist. 5.400 l.y., 50 stars and Cr 419, open cluster magn. 5.4.
|M10 - NGC6254|
Dist. 14.300 l.y.
|Please e-mail to Carlo Corti|
any suggestion and criticism