Welcome to Houston Astronomical Society

by Jim King

Many, maybe most of you, have at least dabbled in the famous Messier Catalogue as a good deep-sky starting point for your observing efforts.  The problem with Charlie Messier is that his catalogue has as a primary purpose, the identification and location of objects that looked suspiciously like comets through his 3.5-inch telescope.  After all, he was a world-renowned comet chaser. He did not want to waste his time looking at/for things that looked like, but were not, comets.

Comes the NGC/IC catalogues.  The New General Catalogue of Nebulae and Clusters of Stars (NGC) is an astronomical catalogue of deep-sky objects compiled by John Louis Emil Dreyer in 1888.  The NGC contains 7,840 objects, including galaxies, star clusters, and nebulae. Dreyer published two supplements to the NGC in 1895 and 1908, known as the Index Catalogues (IC) describing a further 5,386 astronomical objects.  Thousands of these objects are best known by their NGC or IC numbers, which remain in widespread use.
13,226 is a bunch of objects, many of which are low on the exciting scale or are just plain not visible in backyard telescopes.  However, some are quite spectacular and we can all enjoy them with reasonable glass and viewing conditions.  The following list contains a small group of the best NGC/IC objects easily visible in late winter.

By Leland A. Dolan

(From the September, 1987 issue of the GuideStar)

Perhaps one reason I was picked as historian, is that I tend to dwell a lot on the past. I still think of my early years as an amateur astronomer as the “good old days”. The chief difference between, say 1960 and now, is that I could observe a number of Messier objects from my yard, and yet I lived only a quarter mile from the University of St. Thomas. For observing or photographing the Milky Way, I would spend the night at my parents’ home, only a couple of miles west of Memorial Park. Nowadays, to go anywhere where one can observe deep sky objects, requires that two or three hours be spent traveling to and from the observing site.

But, Let’s take a look into the next century. No this article is not going to be a “downer” but an imaginary view of what might be possible in the future. WARNING: This article is perhaps outrageously speculative, and will not appeal to the hard-bitten realist. But, for those who like to dream, dream along with me.

By Don Selle

Part 1 of Getting You Exposed, dealt with the concept of Total Exposure time and Exposure Value. It also provided some rules of thumb to help you estimate the Total Exposure time required for various types of targets using your own imaging rig. Having a good idea of the Total Exposure is certainly essential for acquiring high quality data on the low light level targets we image, but it is only one factor we need to consider.
Since most targets will require several hours of Total Exposure time to acquire enough data to assemble a quality image, we will typically acquire that data using multiple sub-exposures (aka sub-frames). The exposure time for each sub-frame when summed will equal the Total Exposure time of the acquired data. 
When you think about it, this makes sense. You wouldn’t want to take hours long single exposures as too much can happen. Satellite photo-bombs, mount tracking errors, autoguiding errors, operator error and things that bump your tripod in the night can ruin your sub-frames and result in the waste of a lot of time. Even back in the days of film, to avoid these risks, astro-imagers took multiple exposures, developed them, then scanned and electronically combined them to reduce the noise in the image.