FreeLists / az-observing / [AZ-Observing] Re: M33's HII Regions

[BillFerris@xxxxxxx]

Jack Jones wrote:
> Your perusal of M33 is most interesting and informative. I was wondering
> what is the easy way to make these arcminute measurements in the field. Do
> you just guesstimate or have a template or reticle in the eyepiece, or use
> a high-power eyepiece with a small known field or what?

In the field, I compare the relative patterns of stars and objects as plotted 
on charts, captured in photos/images and presenting at the eyepiece. This 
almost always allows me to make a proper ID of an object.

Then later at home, I use MegaStar to determine actual distances and sizes. The 
object size estimates are for the apparent size in the eyepice, which is 
usually recorded in a sketch. With enough field stars, I can make a 
determination that the object--a galaxy for instance--is as "big as the 
distance between those two stars" or something like that.

Open star clusters usually appear as large in the eyepiece as they are recorded 
in the professional data, unless the outermost members are quite faint. High 
surface brightness planetaries often are recorded at their official size or, 
perhaps, just a tad bit smaller. Globulars and galaxies often appear 
significantly smaller in the eyepiece of my 10-inch than their official sizes 
as recorded by the pros. Often, my visual observations record objects between 
50% and 75% the official size.

Anyway, getting back to my recent posting on the HII regions in M33, the 
distances I used in that posting were determined using MegaStar.

Regards,

Bill Ferris
Flagstaff, Arizona
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