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PostPosted: Sat Feb 02, 2019 8:52 am 
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Joined: Sun May 11, 2008 6:11 pm
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Location: Portslade, Sussex Lat 50deg 51min Long 0deg 13mins West
During the Lunar Eclipse there were a number of reports of a flash produced by a meteoroid hitting the lunar surface and even being video-ed. Examining one of my printed photographs of the eclipse there is an obvious sharp white/bright spot very near them limb more or less nearest to Mare Humorum. The time on the photograph is 0432 UT although a correction of 10 minutes is necessary to get the correct time (I must really set it right!). This position is exactly where the various photographys on the Internet show this "spot" and some consider it to be an impacting meteoroid. As I have printed this out, I have erased the image from the camera, and cannot give any more technical details at present. (added later...a colleague copied all my eclipse pictures before I erased them so should be able to supply this info later). Before seeing the report, I imagined that it was possibly a photo fault or passing satellite or some other artifact, but I am now wondering if I have, just by chance, captured this flash and if it could actually be the meteoroid hitting the Moon. Any comments, did other observers here record it? The timing of the reported flash would be very useful to confirm or immediately deny this as a possibly. Regards maf.

(Added info : ISO 5000. I sec. f6.5. Equivalent fl 215 mm +3.00 eV . Will endeavour to post a photograph here soon. Camera is a Canon Powershot SX50 HS. The time on the camera is given as 04:32:28 but needs a correction of about +10 minutes, so should be about 04:42 UT.)

(Added info: I now notice that here is a very similar photograph to mine - which I still cannot figure out how to paste here - by Jamie Cooper on the SPA news page, with the time of 04:41 thus confirming my timing.)
Regards maf.,


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PostPosted: Sat Feb 02, 2019 4:35 pm 
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Joined: Fri Dec 10, 2004 10:34 pm
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Location: Surrey
A tip for observers using digital cameras

To ensure that I can work out what time an image was taken I usually take an image of a clock before and if I remember after observing.

The image below shows a typical timing shot. I also rename my images by the camera time usig exiftools. As a result it is easy to see the camera time for the attached image was 20190119-100510 and the clock display shows it as 1005215 so my camera was 5 secs slow.

You don't actually need to rename the files - the exifdata for the file will show the actual time the image was taken. All you need is a piece of software that shows the exif data on your images.

One small note of caution it is not clear how accurate radio synchronised clocks like these are. They are advertised as accurate to one second in several thousand years but that is only true when they synchronise which is normally only a few times a day. Between that the clock free run and the accuracy depends on the performance of the local clock oscillator.

A better option may be a clock on a GPS as I beleive these are continuously synchronised to the Satellite clock.

John


Attachments:
File comment: Camera image time calibration
20190119-100510-small.jpg
20190119-100510-small.jpg [ 185.48 KiB | Viewed 504 times ]

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PostPosted: Sat Feb 02, 2019 4:58 pm 
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Joined: Sun May 11, 2008 6:11 pm
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Location: Portslade, Sussex Lat 50deg 51min Long 0deg 13mins West
I realised that the clock on the camera was about 10 minutes adrift by photographing a clock which is believe to be right and then comparing with the time on the camera on the image. Most photographs that I take are not very time-dependent, but in this case it was important! Many photographs taken by others often do not include even the date when printing them out. Of course nowadays many people do not even print their photographs but end up with thousands upon thousands of images in their computers. regards maf


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PostPosted: Sat Feb 02, 2019 10:09 pm 
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One thing I should have addded for the information of anyone who may come across this thread in the future is that you have to be very careful with Summer Time (Daylight Saving Time). The EXIF standard for camara image Metadata has no concept of Summer Time. The times are normally shown as what you have set on the camera. If you try to keep the camera on UTC during the time that Daylight Saving is in force some cameras will automatically change their time to match the computer time if you connect them to download.

Taking an image of a clock that shows that Daylight Saving is in effect before & after observation provides some protection. If you observe during the night the clocks spring forward or worse still fall back in the Autumn be very careful with the times.

Don't forget the times on digital TV are out by quite a long way - the new year started 10 seconds late if the TV was to be beleived ! However the fireworks started on time by my synchronised clock - the digital TV encoding and decoding delays the signal by several seconds which is the reason we no longer have time signals on the TV.

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PostPosted: Sun Feb 03, 2019 5:14 pm 
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Hi John,

I have about six or more radio controlled clocks, mainly digital but also 10 inch? wall clocks.
The biggest difference between clocks is normally about 0.5 seconds, unless one of the clocks loses the radio signal, when the difference can increase to any amount over time.
The largest difference I have noted for the clocks receiving signals is almost 1 second.

If I switch T.V. channels say from Ch1 or 231 Freeview there is a couple of seconds delay and one can hear and see the same thing twice.

I bought about ten radio controlled projection clocks for £2 each from the charity shop. They were new I think from a WHS donation. Most work well over say ten years. The display gets dimmer to nothing as battery power fails, but this doesn't seem to affect the time until the battery is almost flat.

One that I have had for about twenty years gives moonrise, moonset etc. also moon phase.
Pressure, pressure change, temperature inside and outside. This is very useful.
There is or was a Celestron version also.

One of my cameras has photos marked to the second, but most are to the minute.

Regards,
David


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PostPosted: Sun Feb 03, 2019 7:21 pm 
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David et al,

In terms of accurate time if you have a GPS connected to a Linux Computer you can use GPSmon to see the time - however I am not totaly convinced if it shows the time from the GPS or the time from your computer clock. Whern I turn my Raspberry Pi on it shows a time before the GPS satellites appear to have locked. It could be the computer time or else it could be the time from the first GPS Sattelite it has found - difficult to tell as it takes time from aquiring the first satellite to getting a position.

My Raspberry Pi is also confused as it runs NTP so obtains a time from remote servers, the intention is that it obtains GPS time and that is corrected to UTC. My GPS has a 1 PPS output but only seems to be the time service NTP uses on rare occasions.

In terms of image timings on cameras I think the EXIF spec says that the time shall be recorded to 1 sec though what is shown on an image is not specified. You should be able to read the actual image time with any decent software that shows the EXIF data. Windows only shows the time to the minute in the file properties but as I said you need some decent software !

One of the problems with EXIF data is that the time resolution is 1 second. As it is now easy to take multiple images in a second this can result in them all having the same apparent time.

Regards

John

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