Observation of Venus on the 25th January 2025

Last Saturday we had a clear patch of weather and so late afternoon, just after sunset, I thought I would have a look at Venus again to see how things have changed since half phase (dichotomy) was reached. Here is the page out of my notebook:-

The angular distance between Venus and the Sun is now decreasing but it is still pretty much in the same part of the sky as before. At the time of the observation it stood at 23 degrees above the horizon in the SSW. There was a bit of thin cloud about which glowed an orange colour in the sunset. I used the same set up as previously but due to how Venus is orientated the terminator was much more tilted than before and so I ended up just drawing it as I saw it in the eyepiece.

As you can see from my drawing the phase is now looking much more crescent in appearance. It has noticeably gone from convex to concave. This time I paid much more attention to the terminator itself and it is clear that it isn't a well defined boundary but has some fuzziness to it. I have tried to represent this in my drawing. What's more I thought I could at times detect a bit of cloud shading near the terminator - this is where there are subtle differences in the brightnesses of the clouds on Venus. Again I have very tentatively put what I saw in my drawing. One other thing was that the cusps looked somewhat brighter than the other parts of the illuminated side.

I had drawn myself some new phase diagrams on the computer to show what the predicted phase would look like from 40 to 50% in steps of 1%. With these on my phone I could compare them directly with what I saw at the telescope and I estimated that the phase was 41%. The predicted phase was a bit more than this at 42.5%, a difference of 1.5%. Here is what 42% should look like:-

All text and images © Duncan Hale-Sutton 2025