[Aavso-photometry] FITS and observation time

[Jeff Hopkins]

Hello Arne,

Thanks for the reply. I will do more experimenting on this. I see on 
the DSI Imaging list there has been a request for new features for 
the software. Perhaps Meade will improve this in the future.

Jeff

At 09:42 -0700 07/26/2007, arne wrote:
>Jeff Hopkins wrote:
>>  Normally I observe long period eclipsing binaries where precise time
>>  to the second or millisecond is not a factor. Recently I have started
>>  a mentor project using the fast eclipsing binary sz Herculis. I am
>>  using AutoStar and found the FITS time indication is off. It seems to
>>  be the time the file is saved. I started a one-shot 15 second
>>  exposure at 05:02:30. The end time should have been 05:02:45 or
>>  close. The FITS Header indicated 05:02:57.
>>
>>  If the difference is fairly constant, it could be compensated for.
>>  However, things get more complex when images are stacked and during
>>  the stacking when some images are not stacked due to poor quality.
>>
>>  How has this been handled by the AAVSO?
>>
>The AAVSO assumes that the submitted time is for the midpoint of
>the exposure.  Calculating this correctly is left up to the observer.
>
>Not quite sure how you would get 05:02:57 from your above example.
>Does Autostar take 12 seconds to download the image?  Certainly
>the written time cannot reflect the end-time of writing an image
>since the header gets written first.
>
>Most software packages modify the header time when stacking
>images.  There was an extensive discussion about this a couple
>of years ago on this list, but I'd presume that each software
>package writes things differently today.
>Arne
>_______________________________________________

-- 
Jeff Hopkins
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Counting Photons
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