NavList:

Art Leung, you wrote:
"This time, I was 'only' 15 minutes off."

It's hard to know what to make of this latest post, Art. Without data, there's not much to do :). I had some thoughts on your 5 minutes error yesterday, but now you say you have a 15 minute error? That just can't be. Either that's a typo of some sort, or you mean minutes of time (?), or you're doing something radically wrong, or there's something radically wrong with your sextant (like a loose micrometer drum).

A few thoughts and replies to your questions:
1) There's nothing wrong with trying Sirius. No doubt someone will be thinking right now, "Sirius is a horrible choice for lunars!" because it's not one of the nine traditional lunars stars. That isn't true.
2) You can estimate your distances in advance by looking them up. No lunarian ever worked "in the dark" [metaphorically speaking :) ]. Historically they always had access to tables of predicted lunar distances. You can use the tables from my predicted distances web app or various other sources.
3) Yes, you used the proper limb of the Moon. When in doubt, ask yourself where the Sun is. For example if it's late evening twilight, you know the Sun is not too far below the horizon in the west. If you can see the Moon, and it's not right on the horizon in the east, then the bright, smooth limb has to be the one facing west. You can also base your judgement on the dates on a good astronomical calendar (many common calendars will suffice). In evening hours, if it's before Full Moon, then the good limb of the Moon is facing the western hours. After Full Moon, the good limb faces the eastern horizon. The only catch is when it's the middle of the night and you're not quite sure where the Sun is by compass bearing.

When you're trying first to get a star in view, there are a few things you can do. First, you preset to the right distance (as above). This helps enormously. Next for any objects close to the ecliptic like the Sun, planets, and many of the standard lunar stars (not Sirius in this case, and not Altair, for example, among the standard lunar stars), the other object will be lined up perpendicular to the horns of the Moon. You can use this. Sight on the Moon. Then rotate the sextant until the Moon's horns are horizontal in the field of view (horizontal in the same sense that they would match the orientation of the sea horizon seen on a standard altitude sight). The other object should pop right into view. Also before you look through the sextant, hold the instrument out at arm's length and line up its frame so that is parallel to the geometric plane created by the Moon, the target star, and your eye. This will give you a good sense, good "muscle memory", as they say, of the proper orientation of the instrument when you take your sight.

Frank Reed