Venus approaching its inferior conjunction

Venus has been a bright light in the evening sky for several months now, but that’s all about to change. As an inferior planet (that is, a planet that is closer to the Sun than the Earth), its phase is waning as it approaches its lining-up point between the Earth and the Sun on 3 June (the ‘inferior conjunction’). At this point it will have 0% illumination and then afterwards switch to being a morning planet again.

This composite image shows my astrophotographs of Venus taken on 19 April (left), 2 May (centre), and 19 May (right). You can see the phase difference between them, as well as the difference in apparent diameter as Venus swings round the part of its orbit closest to Earth.

The image taken on 19 May is likely to be my last one before the conjunction. As Venus lines up with the sun, it sets progressively closer to sunset, meaning it is only visible for a short period of time each evening before setting. Of course, it’s close to the horizon during this time, where there is poor seeing and plenty of horizon clutter. I had to move my telescope three times on 19 May, trying to find a clear view around rooftops and trees. I eventually managed to catch a few minutes in the front garden!

The unprocessed video captured on 19 May is below. Venus is wobbling all over the place due to the long column of turbulent atmosphere near to the horizon (even though the astronomical seeing was as good as I’ve ever seen it in the UK). Towards the end of the video, the view darkens as the roof of a nearby house begins to obstruct. It was only by selecting and working with the best of these frames (‘lucky imaging’) that I got anything worth showing at all.


  • 19 April 2020: 1698× 1-ms light frames at gain 900 (600 best frames stacked)
  • 2 May 2020: 2375× 1-ms light frames at gain 900 (400 best frames stacked)
  • 19 May 2020: 2016× 1-ms light frames at gain 10000 (504 best frames stacked)
  • 60× dark frames
  • No other calibration frames


  • Explore Scientific ED 102 mm Apo f/7 refractor
  • Sky-Watcher EQ5 PRO SynScan GOTO equatorial mount
  • Altair GPCAM3 290C colour camera (with UVIR window fitted)
  • Celestron X-Cel LX 3× Barlow


  • Sharpcap
  • PIPP (Planetary Imaging Preprocessor)
  • AutoStakkert!
  • Registax
  • Photoshop

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