Re: (IAAC) Obj: S518 - Inst: 6" TEC Mak, f12, GP
Thanks William. Yes, PA would be a consideration. And, of course, the
formula at the celestial equator would be T=D (time = distance). One minute
on the stop watch would be one minute of arc. There must be a conversion
function involving declination as the only(?) variable.
From: William Schart <email@example.com>
To: firstname.lastname@example.org <email@example.com>
Date: Saturday, January 05, 2002 10:01 AM
Subject: Re: (IAAC) Obj: S518 - Inst: 6" TEC Mak, f12, GP
>This is possible. However, there are some problems.
>First of all, you have to take in account the position angle of the
>object you are measuring. Obviously, if the PA is exactly along the E-W
>line, it will take longer to drift than if the orientation was
>otherwise, and a N-S orientation would be impossible.
>The % of error increases with smaller objects also, but if you are just
>interested in reasonable estimates, this would not be a problem.
>Somewhere in the past I recall seeing an article about this with a
>formula, but I don't recall the source now. I did some searching on the
>web and couldn't find anything either under "transit timing" (got a
>bunch of astrology stuff here!!) or double stars. Maybe you can have
>On Saturday, January 5, 2002, at 12:34 AM, Don Clouse wrote:
>> Bill Becker wrote:
>>> I was using the data(for sep & pa) from The Night Sky Observer's Guide.
>>> I do have a micrometer ocular but the mounts I'm currently using don't
>>> have drives so making accurate measurements is a bit tough.
>> I "eyeball" angular sizes of objects based on field size. With this
>> for me anyway, it becomes more and more difficult to even get in the
>> "ballpark" as smaller and smaller objects are viewed. It occurred to me
>> recently that it should be possible to estimate sizes by timing the
>> drift of
>> the object off the edge of the field. The conversion of time to
>> would vary by declination and, btw, would seem to be more difficult and
>> consuming the further the object is from the celestial equator.
>> Has anyone attempted this? Is it at all practical? Does anyone know if
>> conversion formulas are available? Does any of this make any kind of
>> Bill's statement seems to imply that it might be possible. But I don't
>> understand what a drive has to do with it. It seems as though you would
>> turn off the drive to do the measurement.
>> Any insights would be appreciated.
>> Don Clouse
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