31 January 2015

Wide-Field Observing

I recently posted an observing plan to the Deep-Sky Planner Plan Library  containing most of the objects that appear in the "Wide-Field Wonders" article in the 2013 RASC Observer's Handbook. (The article also appears in the 2015 edition.) While most of the objects are nebulae and clusters, a few are more esoteric objects that aren't found in typical catalogs - things like molecular clouds. This plan contains an excellent variety of imaging and viewing targets, so I encourage readers to check out the article to get background information.

Observer's Handbook from
Royal Astronomical Society Canada

Wide-field observing (both visual and imaging) generally requires a rich-field telescope, binoculars, or a fairly fast telescope with a long focal length eyepiece. These objects often have low surface brightness, so a dark location is definitely indicated.

Wide-field observing can be a nice change of pace if your usual deep-sky observing includes galaxies, planetary nebulae and such. For example, I've observed the Veil Nebula in Cygnus dozens of times with various telescopes. I always enjoy viewing it with a UHC filter and magnification around 100x. The telescope I use most often these days is a 14.5" f/4.5 reflector. My rather ancient 20mm Nagler eyepiece produces magnification of 96x with a field of view of about .86° with this telescope. I've used this combination of equipment for several years, so the end result is somewhat expected.

14.5" f/4.5 Reflector

I got a new lower power eyepiece a year or so ago that was a game-changer on things like the Veil. The new eyepiece is a 31mm Nagler which produces 61x with FoV of 1.3°. It turns out that the view with the 31mm eyepiece allows me to see most of the nebula at once. The view with the 20mm requires a lot of scanning around to view the entire nebula. While the detail is much greater with the 96x view, the ability to 'get it all' at 61x is a welcome new capability. I've also observed the Veil through a friend's Tele Vue-NP101 (101mm, f/5.4) with a 31mm Nagler. The view was stunning and quite different from my usual result. That view really inspired the purchase of the 31mm eyepiece.

TeleVue's 31mm Nagler

From this I think it is fair to suggest that we get into familiar patterns with our observing - both imaging and visual. A simple change like using a different eyepiece can produce a very different view, even with an object that is very familiar. Perhaps we should take the next step with this by pursuing an observing plan that includes objects well off of our beaten path. The "Wide-Field Wonders" plan may be such a refreshing change of fare.

01 January 2015

Robert Trumpler's Open Clusters

An observing plan called the Trumpler Clusters was created recently for Deep-Sky Planner and posted to the Plan Library. Licensed users can view and download the plan by logging into the Deep-Sky Planner Community and browsing for the plan in the Library (Help | Community Page).

Open clusters are wonderful observing targets during the present season. Some of the Trumpler clusters are a bit dim for common binoculars, but a telescope serves well when observing them. The Trumpler clusters are located between declinations +63 and -63, so many are visible to both northern and southern hemisphere observers.

I have looked for Robert Trumpler's original paper for years without finding it. Phil Harrington's recent article on Cloudy Nights included a link to Trumpler's original paper which is available on ADS at Harvard. (Thanks go to Phil for providing this!)

Trumpler 36 / IC 1311
© 1995 by the Association of Universities for Research in Astronomy, Inc
Trumpler's paper was published in 1930 and sought to define all known open clusters. Thirty-seven of the objects in the list were unknown when the paper was written, and these have become known as the Trumpler clusters. All but Trumpler 36 are still recognized in today's literature. Trumpler 36 is a bit of a riddle, although it seems to be IC 1311. Trumpler's paper also included a study of cluster diameter, distance and magnitude of member stars. It's a very interesting paper to read even some 85 years later. Any dedicated observer of open clusters should have a look at it.

The observing plan that appears in the Deep-Sky Planner library includes updated coordinates and size information from "Optically Visible Open Clusters Catalog" (Dias+, 2002-2012). Trumpler's original classifications are also included in the plan. The well-known Trumpler classification system encodes concentration, richness and brightness as follows:

I=detached cluster, strong concentration
II=detached cluster, little concentration
III=detached cluster, no concentration
IV=undetached cluster

1=equal brightness
2=medium range of brightness
3=bright & faint members

p=poor, < 50 members
m=moderate, 50-100 members
r=rich, > 100 members

Enjoy observing the Trumpler Clusters in the new year!