Cataloging What's In the Sky (Part 1)

Each year at Christmas and Valentine's Day the airways are filled with advertisements to "name stars". The various companies in this business vary in the degree that they are candid about what they are selling. The best admit that whatever they produce is "For Entertainment Only"¹. Others operate closer to PT Barnum and his This Way to the Egress which was accurate, but intentionally misleading. That leads to the larger question of how is stuff really named. I will explore that question over the next few columns.

The simple answer is that for objects outside of the solar system nothing is named (or at least new names are not being added). Instead as technology has improved a number of people have cataloged objects in the skies with different degrees of precision. Each of these efforts has produced its own catalog. These catalogs in some cases overlay existing work. In others, they catalog known objects with interesting behavior. Finally, they may catalog new objects that were beyond the ability of previous technology to record.

In this Ephemeris we will take a look at the evolution of cataloging deep sky objects. Deep Sky Objects are everything except individual stars.

Catalogs and Lists

For the purpose of this series I will define two terms; catalog and list. A "catalogue" is a primary reference giving the location and description of an object as produced by some form of formal survey. We will mention several in this paper and subsequent papers.

I will be using the term "list" to refer to a secondary compilation of objects. A list refers to object as entries in one or more catalogs rather than trying to act as a definitive reference.

In the Beginning

Man has been looking at the skies for thousands of years. Early civilizations recognized that the sky contained important clues that it was in the best interest of society to understand. After all, the rising of the sun gave clues to when to plant, when winter began, etc. Shamans in early societies taught themselves the sky, which allowed them to predict astronomical events². They soon noticed the wandering stars and added the 5 visible planets to their developing religions. Seafarers learned to use the stars to navigate and gave them names.

About 3000 stars are visible in the darkest skies. Only a handful of deep sky objects can be seen unaided. Among them Andromeda, several open clusters (Hyades, Pleiades, Double Cluster, Praesepe), and M42. The introduction of the telescope in the 1600s allowed observers to see many more objects.

The Messier List

By the late 1700s telescopes had improved to about the level of today's beginner scopes. The French Comet hunter Charles Messier began systematically recording the locations and descriptions of a number of objects. References state that he did this so he would not confuse them with the comets he was hunting. From 1758 until 1781 he created and then published his first list of 103 objects. In subsequent years he refined his list and added several more bringing his total to 110 (or 109).

The Messier List remains the best "Best of" list in the sky.

The Herschels

Across the channel William Hershel was also cataloging. Hershel became the Royal Astronomer in 1781 following his discovery of Uranus. That gave him the resources to begin a systematic cataloging of the many objects visible in late 18th Century telescopes. He published his first catalog of about 1000 objects in 1786. By 1802 he had cataloged almost 2500 objects. His son John carried the effort to the southern hemisphere setting up in South Africa in 1834 and adding the southern objects to the rapidly growing number of catalogd objects. John eventually produced the General Catalog in 1864.

The Herschel family was not alone. Others were busy at work doing their own cataloging. These other catalogs varied greatly in quality leading to much confusion and overlap³ .

The New General Catalog (NGC) and Index Catalog

By the late 1800's so many different catalogs existed that it was time to integrate them into a single list. J. L. E. Dreyer attempted to resolve the conflicting discovery claims, descriptions, and positions. He published a revised New General Catalog in 1888.

Once again the increasing ability of instruments demonstrated the NGC was not complete. Dreyer subsequently published the Index Catalog as two supplements (1895 and 1908 ) to the NGC bring the total number of cataloged objects to about 13,000.

More importantly for amateurs the combined NGC/IC represents virtually all non-stellar observable objects.

The Modern NGC/IC Project

Unfortunately even after the great work of Dreyer the NGC was still imperfect. Starting in the 1990's a group of professionals and amateurs set out to review all of the original material, correct the positions, and resolve the discrepancies. Steve Gottlieb spoke to SJAA in 2005 as the project neared its completion. Most of the NGC/ IC objects are within the abilities of a skilled amateur observer with a modern telescope. Volunteers like Steve have re-observed all of the NGC and IC to add contemporary descriptions and correlate the original observations to modern Sky Survey images.

Summary of Part I

The NGC / IC catalogs virtually all of the objects of interest to an Amateur. The original Messier list was subsumed by the Herschels' and Dreyer's work and should now be considered a list of interesting NGC objects. Others have made lists of their favorite objects. We will talk about some of these lists in future months.

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Notes:

1. For Example StarNamer.com states (in very small letters) “Our star naming is not recognized by the scientific community. Your star’s name is reserved in Starnamer records only”

2. “How the Shaman Stole the Moon “, William Clark, http://williamcalvin.com/bk6/index.htm

3. Steve Gottlieb in his NGC/IC presentation to SJAA