Three days ago we had some more cold clear weather late in the afternoon. Venus is now quite a prominent object in the sky and seems very bright. It will get brighter still even though the illuminated area of the planet will be shrinking. This is because Venus is getting closer to us as it heads towards inferior conjunction. Maximum brightness will be around the 20th February when it reaches magnitude -4.9. On the 9th it was 1 day away from greatest elongation east and at about 26 degrees high in the SSW.
I was again out the front of the house with my 102mm Celestron:-
The most important thing about this observation was that in my opinion dichotomy (or half phase) has been reached! This was the feature that I had been waiting to see these last few weeks. I was again using an eyepiece and barlow lens combination that gave a magnification of 147x. When the image had settled enough (the breeze and seeing playing its part) I almost felt like I could detect some concavity in the shape of the illuminated side (which would mean that the phase was less than 50%). It definitely looked like half phase at the very least. This is against what would be expected for a solid sphere at Venus's current position. The predicted phase on this date is still 51.6% and it indicates to me that the phase anomaly (that dichotomy is observed about 4 days ahead of its prediction) is a real effect. Why this is so may be to do with the atmosphere of Venus and I will try and explain this another time.
One effect that I haven't been able to understand is that, to my eyes, the northern cusp still looked slightly rounded with the indentation of dark eating into the light side. This has been apparent all through this string of recent observations (the southern cusp on the other hand went straight to the edge with no deviation). I will be interested to see what happens a few days after the predicted date of dichotomy.
All text and images © Duncan Hale-Sutton 2025
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