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 
better luck.

William Schart

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 
> method,
> 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 
> distance
> would vary by declination and, btw, would seem to be more difficult and 
> time
> 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 
> sense?
> 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.
> Thanks,
> Don Clouse
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