"OLTRE MESSIER" ("Beyond Messier")
"OLTRE MESSIER" ("Beyond Messier") is a 240-page book that could be considered the natural continuation of my first volume titled "Catalogo Messier". The book has been published in 1999. The ISBN (International Standard Book Number) of this book is: 88-95650-10-4. In it 200 deep sky objects are described, not included in the first book but still within the reach of the most common amateur telescopes.
After Charles Messier's pioneeristic and adventurous observations which, in 1784, led to the publication of the final version of his well-known catalog of celestial objects, progress in astronomical observation started taking gigantic steps: indeed, the greater optical power and better quality of the new telescopes unveiled a sky of ever more numerous weak and hazy looking objects which, in those days, were generically referred to as "nebulae".
The Frenchman's work was immediately carried on in Great Britain by William Herschel whose tireless observations and his "scanning of the heavens" he published in three short papers in 1786, 1789 and 1802, where he announced the discovery of more than 2500 new star clusters and nebulae.
At times there is a tendency to exaggerate the work of famous people of the past, but in the case of William Herschel a simple glimpse at the list of his discoveries and intuitions is enough to leave one breathless. At a time when there was no particular distinction between professional and amateur astronomers, the "star-lover" William Herschel managed to approximately guess not only the presence but also the shape of the Milky Way based on his careful observations and by counting the number of stars within 3400 little areas spread all over the sky. Fortunately for Herschel his period was that of the enlightened King George III who was very taken with his work and frequently brought his guests to admire Herschel's enormous 48-inch telescope, which the king's generous contributions had helped to build.
Of the many things Herschel discovered, he also noticed that by increasing the resolution power of telescopes, many nebulae resolved into swarms of weak stars: thus he accepted the hypothesis that most nebulae may be nothing but enormous star systems isolated in space, similar to our Galaxy, but extremely far away. This hypothesis had originally been made, a bit fancifully, by Thomas Wright in 1750, but later redefined and made more accurate by Immanuel Kant in 1755. To give an idea of how ahead of the times this was, it is sufficient to remember that proof of galaxies external to ours was only reached in 1923, thanks to the work of Edwin Powell Hubble carried out using the then very new 2.5 meter diameter reflector telescope on Mount Wilson.
Furthermore, Herschel established the existence of a kind of small nebulae, generally round in shape and often bearing one little star in the center, which he called "planetary": he thought that he was looking at young stars surrounded by a planetary system in formation. Today, however, we know that, on the contrary, they are stars that have reached a very advanced stage of the evolution. He also discovered that some nebulae, like the well-known M 42 in Orion, maintained their haziness even when seen through telescopes of greater dimensions: instead of resolving into stars, they looked more and more like a huge cloud. Therefore, he thought that this kind of nebula may be the "matrix" from which the stars derived, and he explained his theories in two papers, in 1811 and 1814. There, then, was a really remarkable intuition of strongly evolutionary content, at a time when the world still thought that celestial bodies were practically unchanging and incorruptible objects: Herschel's ideas were surprising and very much ahead of the times when we think that the "father of evolution" Charles Darwin, was barely two years old.
William Herschel's splendid work was carried on by his son John, a scientist of broad culture and a keen observer. So the work of cataloguing any objects in the sky that looked nebulous found natural continuation, particularly in the southern emisphere: John Herschel gathered his father's observations, and added about the same number of his own, to the catalog he published in 1864, the "General Catalogue of Nebulae" (abbrev. GC) containing a substantial 5079 objects.
The next step was taken in 1888 when the Danish astronomer Johan Ludvig Emil Dreyer published the "New General Catalogue of Nebulae and Clusters of Stars" (abbrev. NGC), basically on John Herschel's work, but now listing 7840 objects. Dreyer's catalog, except for Messier's concise catalog, was and still is the most popular catalog even today: though out of date in the professional field, where the frontier is naturally much further on, it is still widely used in the amateur field. Indeed, with few exceptions, nearly all deep sky objects, accessible with an average sized, non-professional telescope, have an NGC catalog number. In 1895 Dreyer produced the first "Index Catalogue" (abbrev. IC), listing another 1529 objects; then the "Second Index Catalogue" in 1908 which added another 3857 objects, totalling 5386. Overall, Dreyer lists an astounding 13,226 celestial objects.
By now the art of photographing the heavens had been developed: France, Europe and a fairly big part of the world were at work to complete the ambitious task of compiling the photographic atlas Carte du Ciel. Meanwhile in California, Edward Emerson Barnard was using his lenses to take his historical photographs of the Milky Way, that thickly star-populated highway in heaven, with its clouds of apparently dense stars, so incalculably numerous. After patient hours of waiting for the emulsion to pick up the light, the sky began to reveal its weakest, most elusive and distant objects on the film. Each new picture showed new objects, new star clusters and new nebulae, until there were so many that the idea of "discovery" began to lose its meaning already at the beginning of the 20th century. Consequently, the idea of compiling a single catalog for all the sky's objects proved unfeasible. Hence professional astronomers started specializing in different fields, creating catalogs that were no longer general but that grouped specific kinds of objects. The pioneering days of astronomy were over.
The original NGC and IC catalogs were reprinted in 1953 by the Royal Astronomical Society: however, the numerous uncertainties and mistakes (in particular in position: Dreyer found more than 700) led American astronomers Jack W. Sulentic and William G. Tifft to publish the "Revised New General Catalogue" in 1973, later updated in the 1980 edition. Though an admirable piece of work, the catalog lists all the NGC, but none of the IC objects. A complete edition which also contains all Dreyer's 13,226 objects was finally printed in 1988, the "NGC 2000.0", compiled by Roger W. Sinnott.
"Oltre Messier" describes 200 celestial objects, mainly belonging to the NGC catalog, but not part of the Messier catalog: practically all of them can be easily viewed through a non-professional telescope of about 6 inches in diameter in sufficiently clear and dark sky conditions. Except for some the IC objects, there are very few objects named after the astronomers who discovered and catalogued them: Blanco, Collinder, Melotte, Stock and Tombaugh; there is also an object taken from the UGC ("Uppsala General Catalogue of Galaxies"). The aim of "Oltre Messier" is basically intended for observers living in the mild climates of the northern areas of our Earth. The choice of objects covered takes into account some parameters: as far as galaxies are concerned, they are limited to those of 10.4 magnitude considering, for their negative Declination, an atmospheric absorption curve typical of a clear sky, even though not as exceptionally dark and transparent as can be found high up in the mountains. Indeed, seen through average to small sized telescopes, galaxies appear very weak and hazy, so we have not included any object of the southern hemisphere since it would be too difficult to see from mid-northern latitudes: there are so many galaxies to choose from, so we chose those easier for everybody to see. We have, however, exceeded Charles Messier's seeing limit by 0.2 magnitude. His weakest catalogued galaxy is M 91 of 10.2 mag: but what a difference! The same applies for globular clusters. Choice fell on those of up to 10.6 mag, but for these the atmospheric extinction curve is less marked than for galaxies since globular clusters nearly always have a luminous and visible center.
Of the 1200 and more open clusters of our Galaxy, we chose the most spectacular and striking, so magnitude limit is at 8.6, overlaid by curve which takes into account the atmospheric absorption load of objects that pass low in the meridian of mid-latitudes skies. Furthermore, none of the open clusters, classified by R. Trumpler in 1930, and considered as "poor" or as "not well detached from surrounding star field" have been included except for clusters of at least 50 stars, in accordance with G. Lynga's count of 1983.
Although this book is mainly intended for visual observing, some of the best known emission and reflection nebulae could not be left out. Weak and elusive to the eye, they readily and easily become visible on film. A normal telephoto lens of only 135 mm focal lenght is sufficient to photograph them.
However, it was more difficult to choose the planetary nebulae. Indeed, on the one hand some of the smaller sized planetary nebulae frequently have a very brilliant surface and these are, therefore, generally clearly visible through a telescope: in choosing, we avoided the very small objects since it is usually very difficult to identify them against the background of stars. On the other hand, the wide planetary nebulae are quite easy to photograph, but their surface brightness is so weak that even using a medium to large sized amateur telescope, it is still fairly difficult to identify them. Hence our choice of medium to small sized planetary nebulae of average to high superficial brilliance.
The physical data of the objects described are useful to understand some of the fundamental and intrinsic characteristics of the objects themselves; a step beyond the pleasure of simply looking at them. Take, for example, the actual diameter of the things we see up there in the sky, or, to give another example, the absolute magnitude value of both open and globular star clusters, not to mention the galaxies and other data. All aspects which go further than observing and give us a better idea of how they really are, whether we can see them easily or not. In the case of open and globular star clusters it is interesting to realize the importance of interstellar absorption. This is caused by extremely rarified gases and dust particles that come between us and what we are looking at, and that may absorb up to 90% of the light from the object under observation. In this respect, in connection with galaxies, a corrected absolute Mag value has been given, defined as absolute magnitude of the galaxy supposing this can be seen perpendicularly to its equatorial plane, according to its particular morphological type, and in absence of either internal absorption or absorption on behalf of the Milky Way.
Photographs of celestial objects are nearly always of professional quality. In sky photographs, north is at the top, and east to the left, meaning that we see the objects as they actually are in the heavens, whether through a pair of binoculars or with the naked eye. In telescopes, however, objects appear upside down, meaning that north is at the bottom and east to the right. This can be corrected by using a zenithal prism which switches north back to the top, but east remains to the right. Even though some of the photos of planetary nebulae were in fact taken through the Hubble Space Telescope, many of the others were taken using non-professional equipment, proving how the most dedicated amateurs astronomers are rapidly moving towards what, a mere twelve or so years ago, were the photographic limits of the world's biggest professional telescopes. The application of modern CCD electronic sensors has had a leading role in this extraordinary progress. And it was thanks to these sensors that some American amateurs only recently managed to go beyond mag 24 using only fairly small diametered telescopes.
The only thing left is to wish our readers all the best pleasure in viewing the hidden beauties in our night skies. However, though Charles Messier's catalog has been outdated, and even after having looked at all the objects described in this book, remember that we shall still only just be on the threshold, peeping out at the mind-boggling, astonishing marvels to be found in the immensity of the Universe. In 1725 Isaac Newton wrote: "I do not know what I may appear to the world, but to myself I seem to have been only like a boy playing on the sea-shore, and diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, whilst the great ocean of truth lay all undiscovered before me".