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Re: (IAAC) Obj: S518 - Inst: 6" TEC Mak, f12, GP
Yes, this is basically true. If you want to be really accurate, you have
to adjust to sidereal time, and also take atmospheric refraction into
account. For you purposes, I doubt either is signifacant.
Somewhere I have the instructions for the Celestron Microguide EP with
this formula, but I can't find this right now. It has the annoying habit
of disappearing when you want it and then showing up when you are
looking for something else. If it turns up, I'll send it to you.
William
On Saturday, January 5, 2002, at 10:10 AM, Don Clouse wrote:
> 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.
>
> Don Clouse
>
> -----Original Message-----
> From: William Schart <wschart@hot.rr.com>
> To: netastrocatalog-announce@atmob.org <netastrocatalog-
> announce@atmob.org>
> Date: Saturday, January 05, 2002 10:01 AM
> Subject: Re: (IAAC) Obj: S518 - Inst: 6" TEC Mak, f12, GP
>
>
>> Don:
>>
>> 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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>>
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