Saturday, October 22, 2005

Creating Asterisms: SALC 34 North

This is as good a time as any to document the process of working on a new search area location chart (SALC). Since the current SALC (#53 in Auriga) is rising a little too late these days I'm working on a new chart - SALC 34 (north) in Perseus.

I prefer working on rising SALCs since they are located in the darkest portion of Central Park's night sky ... the northeast.

The 1st night of observing (Mon., Oct. 17th) was under less than ideal conditions. High cirrus impacted the binocular limiting magnitude (BLM) by a few tenths of a magnitude for the 1st hour. The situation improved when the cloud cover started to dissipate.

When viewing through cirrus, stars of magnitude 8.6 and dimmer took some effort to see. Later on stars down to magnitude 8.8 - 8.9 were steadily seen without effort. The total number of stars examined for creating asterisms was 193. This is approximately half of the northern portion of SALC 34.

Time spent observing was 1h40m (9:20p-11:00p). A few minutes were spent talking to passersby about the night sky.

After noting the stars that are easily seen and the ones that took some effort I sketched in a preliminary set of asterisms. While viewing at the binoculars I'll sometimes just note that a star was easily seen by underlining it. Stars taking some effort to see are circled.

At home I create further connections based on what I remember seeing in the field and what appears to make the most sense.

Creating asterisms without sitting behind the binoculars doesn't seem to work even when knowing the BLM. I tried this with SALC 93 in Monoceros. After reviewing these asterisms in the field I needed to redo all of them.

From this chart I'll study the asterisms and revise connections whenever there's free time. Revisions are inevitable when I get back to the eyepieces.

After feeling comfortable with a preliminary version I'll layout the lines with pencil & straightedge. I'll copy these maps since they take time to create.

When I'm very comfortable with the figures I'll go to the desktop planetarium program Cartes du Ciel (CdC) and create an overlay which will become a permanent record of the asterisms. This overlay becomes a part of each chart I work with in the field. CdC makes the process of creating asterisms to display on a chart fairly easy after learning the 'way.'

From these charts I will hopefully develop a familiarity that will obviate the need for working with charts.