Observation by Nick James: Observation time calibration

Uploaded by

Nick James

Observer

Nick James

Observed

2026 May 08 - 22:31

Uploaded

2026 May 08 - 23:29

Equipment

ASI6200MM + Celestron HD11

Exposure

5x10s

Location

Chelmsford, UK

Target name

GPS Block IIIA satellite 2020-078A

Title

Observation time calibration

About this image

When doing astrometry of fast moving objects it is important to ensure that the observation time in the FITS header (i.e. when the exposure starts) is within a fraction of a second of UTC. I've just installed a new GNSS Stratum 1 NTP time server on my network and wanted to test it.

Bill Gray of Project Pluto has an online tool that can generate very precise ephemerides of GNSS satellites for your observatory. This image shows four successive 10s trails of GPS satellite 2020-078A. The blue circles are the predicted position at the DATE-OBS time reported in the FITS header. I've measured the positions of the trail starting points and the exposure start time is within 0.1s of the true UTC time.

https://www.projectpluto.com/gps_find.htm

Files associated with this observation

G14__20260508_223100_ndj.jpg (2.8 MB)

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