Venus in infrared
Several scientifically intriguing features become visible at longer wavelengths
In the last decade, many amateur astronomers have started using filters to image Venus in wavelengths well beyond the visible part of the spectrum. To capture Venus in infrared you will need a filter and a camera to record the images. You will find that infrared filters tend to transmit wavelengths between 685 and 850nm (nanometres); I’ve seen filters centred on 790nm commonly used.
In December 2015, the Japanese Akatsuki spacecraft recorded a strange infrared feature – a vast 10,000km bow-shaped wave of clouds extending from north to south over Venus’s equator. In the years since, a number of amateur astronomers have not only also captured the feature but have tracked it. Interestingly, the wave phenomenon is not always present – in some elongations it has been completely absent. It did return in 2022 and persisted for many months longer than before.
This phenomenon is called the wave discontinuity of Venus and it appears on the day side, usually near the terminator. One explanation for it is that it is caused by the upwelling of air over mountainous terrain. Several scientists have speculated that the discontinuity may be caused by active volcanoes. If you have an infrared filter and camera, try imaging Venus as often as possible, and if you manage to record it, send your images to me at the Mercury and Venus Section of the British
Astronomical Association (britastro.org), of which I’m the director. We compile amateur observations together to detect and monitor changes to the planet. The best time to try this is when Venus is in the gibbous stage, so have a go at any time before dichotomy on 4 June and help contribute to our understanding of this planet.
Another new avenue of exploration for amateurs is in using infrared to image the night side of Venus. In April and May of 2017, Australian amateurs Anthony Wesley and Phil Miles’s night-side images recorded a number of bright spots on the surface, which have since disappeared. Many scientists believe that Venus could still be volcanically active, so one explanation could be that these were active volcanoes. Imaging them on the night side would be a way of proving this. Imaging the night side also requires an infrared filter and camera, but it can only be done when Venus is in the crescent stage. The difficulty comes in that the sunlit crescent can saturate the image, but this stage will be visible in late June, so that would be a good time to try, if you want a challenge.