The Eagle Nebula - M 16 NGC 6611 Bright Nebula Magn. 6.4 - Dist. 7.000 l.y.
Lying some 7,000 light years distant in the constellation Serpens, and in the next inner spiral arm of the Milky Way galaxy from us, a great cloud of interstellar gas and dust has entered a vivid process of star formation. Open star cluster M16 has formed from this great gaseous and dusty cloud, the diffuse Eagle Nebula IC 4703, which is now caused to shine by emission light, excited by the high-energy radiation of its massive hot, young stars. It is actually still in the process of forming new stars, this formation taking place near the dark "elephant trunks" which are well visible in our photographs. This stellar swarm is only about 5.5 million years old with star formation still active in the Eagle Nebula; this results in the presence of very hot young stars of spectral type O6. The cluster was classified as of Trumpler type II,3,m,n (Götz). Some sources have smaller distances for M16: Kenneth Glyn Jones gives 5,870. Götz 5,540 light years. Götz states that this is one of the intrinsically most luminous open clusters, at an absolute magnitude of -8.21.
M 5 - NGC 5904 Globular Cluster Magn. 5.8 - Dist. 24.800 l.y. M5 shows a distinct ellipticity, elongated at position angle 50 degrees, it is thought to be one of the oldest globular clusters, with a computed age of 13 billion years. Its diameter is about 130 light years, making it one of the larger globular clusters. M5 contains the considerably large number of 105 known variable stars.
M13 - NGC6205 The Great Hercules Cluster Magn. 5.9 - Dist. 23.500 l.y. M13 is one of the most prominent and best known globular
clusters. M13 is frequently one of the first objects found by curious sky gazers seeking celestials wonders beyond normal human vision. M13 is a colossal home to
over 100,000 stars, spans over 150 light years across, lies over 20,000 light years distant, and is over 12 billion years old. At the 1974 dedication of Arecibo Observatory, a radio message about Earth was sent in the direction of M13.
A semi-recent estimate of M92's age has given a value of about 16 billion years.
M92 is a splendid object, visible to the naked eye under very good conditions and a showpiece for every optics. It is only slightly less bright but about 1/3 less extended than M13: its 11.2' angular extension corresponds to a true diameter of 85 light years, and may have a mass of up to 330,000 suns.
M 11 - The Wild Duck Cluster - Open Cluster - Magn. 6.3 - Dist. 6.000 l.y. One of the richest and most compact of the galactic clusters. M11 contains an estimated 2900 stars, about 500 of which are brighter than mag 14. An observer at the center of M11 would see several hundred first magnitude stars! The apparent diameter is given with discordant values; Barnard estimated 35', while the Sky Catalog 2000 gives 14'. The age of the Wild Duck cluster has been estimated to amount 220 million years, as its brightest and hottest main sequence stars are of spectral type B8 but also double that value. The higher value is supported by the fact that this cluster also contains many yellow and red giants of absolute magnitude around -1.0.
The Dunbbell Nebula - M 27 NGC 6853 - Planetary Nebula Magn. 7.6 - Dist. 1.200 l.y.
The Dumbbell Nebula M27 was the first planetary nebula ever discovered. On July 12, 1764, Charles Messier discovered this new and fascinating class of objects. This planetary nebula is certainly the most impressive object of its kind in the sky, as the angular diameter of the luminous body is nearly 6 arc minutes, with a faint halo extensing out to over 15', half the apparent diameter of the Moon. It is also among the brightest, being less luminous with its estimated apparent visual magnitude 7.6 than the brightest, the Helix Nebula NGC 7293 in Aquarius, with 6.5, which however has a much lower surface brightness because of its larger extension. The bright portion of the nebula is apparently expanding at a rate of 6.8 arc seconds per year, leading to an estimated age of 3000 to 4000 years. The central star of M27 is quite bright at mag 13.5, and an extremely hot blueish subdwarf at about 45,000 K (so the spectral type is given as O7). As for most planetary nebulae, the distance of M27 (and thus true dimension and intrinsic luminosity) is not very well known. Hynes gives about 800, Kenneth Glyn Jones 975, Mallas/Kreimer 1250 light years. Adopting the value of 1200 light years, the intrinsic luminosity of the gaseous nebula is about 100 times that of the Sun (about -0.5 Mag absolute) while the star is at about +6 (1/3 of the Sun), all in the visual light part of the electromagnetic spectrum. That the nebula is so much brighter than the star shows that the star emits primarily highly energetic radiation of the non-visible part of the electro-magnetic spectrum, which is absorbed by exciting the nebula's gas, and re-emitted by the nebula, at last to a good part in the visible light. Actually, as for almost all planetary nebulae, most of the visible light is even emitted in one spectral line only, in the green light at 5007 Angstrom.
M 71 - NGC 6838 - Globular Cluster Magn. 8.3 - Dist. 11.700 l.y. For a long time, the classification of M71 as a globular cluster was uncertain, many astronomers thought it was a rather condensed open cluster. Nevertheless, there's now some consensus that M71 is a loose globular. According to newer sources it is 11,700 light years distant. Its denser, easily visible core is only about 5 to 6 arc minutes, while in photos it has an angular diameter of about 7', corresponding to a linear extension of only 25 light years, small for a globular cluster. However, faint members have been detected out to a total diameter of 24', making it measure 90 light years. This globular cluster is easy to find and nicely observable even in good binoculars, by locating half-way between Gamma and Delta of that constellation. Medium-sized amateur telescopes are required to resolve this compressed mass of stars, but then even the center is resolved. The cluster is brighter and sharply terminated on the western side, forming a "curving V".
M 30 - NGC 7099 - Globular Cluster Magn. 7.5 - Dist. 26.700 l.y.
Globular cluster M30, at roughly 25,000 light years distance and about 70 light years across, has only about 12 known variables. It is fairly dense and a fine object in even small scopes. The core of M30 exhibits an extremely dense stellar population, and has undergone a core collapse, similar to at least 20 other of the 147 globulars in the Milky Way Galaxy, including M15, M70, and possibly M62. M30 is less loved by Messier Marathoners, as it is often the last missed object of an almost-complete Messier Marathon, a tour for viewing all Messier objects in one night (which is possible near the end of March in moonless nights). This is, however, only because of its location in the sky; otherwise it is a nice object for amateur astronomers.
Constellation pictures are modified screen displaies of Voyager II™ version 2.0 for the Macintosh™, the Astronomy Program of Carina Software, 12919 Alcosta Blvd Suite #7, San Ramon, CA 94583
Date & Time
M 5 - NGC 5904
M13 - NGC6205
M92 - NGC6341
The Wild Duck
M 26
The Dunbbell Nebula - M 27
M 71 - NGC 6838 - Globular Cluster
M 30 - NGC 7099 - Globular Cluster
Home Page
