Observation by Nick James: Sky conditions in Chelmsford

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Nick James


Nick James


2020 May 28 - 23:00


2020 May 29 - 19:45


The Earth

  • C11 Edge HD + FLI6303



Chelmsford, UK

Target name

Sky brightness


Sky conditions in Chelmsford

About this image

Last night was particularly clear in Chelmsford and I did a long run with the telescope pointed at a single object (20th mag comet C/2020 K2). This is a plot of the sky background level from my images computed using Gaia DR2 as a refrence for the magnitude zero point. The field was in Lyra and so was rising through the night and was near the zenith at dawn. You can see the effect of my local streetlights going off at 1am BST (00:00 UTC).  The Moon set at 00:54 and the darkest sky conditions were just before dawn when I reached 19.1 mag/arcsec^2 at around 01:00. Brightening due to the dawn was detectable around 01:10 UTC when the Sun was around 14.5 deg below the horizon. Nautical twilight for here last night started at 01:56 UTC.

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