Venus 22/8 and 28/8 - in search of dichtomy

[DarkerSky]

I have been observing Venus regularly in the morning sky since early July with my 8.5" scope. Have been watching the illuminated phase grow as the planet has shrunk in size. According to nakedeyeplanets.com dichtomy, which is when the phase is exactly 50% at greatest elongation for the sun, occured 15 August. But as those of you who watch Venus regularly know the actual observation of a 50% phase at greatest elongation is rare.

For morning apparitions it seems that observed dichtomy occurs some days after when it should. From my observations over the past week this seems to be the case (from my point of view anyway).

On the morning of 22/8 ( a week after greatest elongation) I saw Venus still as slightly crescent. There wasn't much in it, but towards the poles the lit portion of the disc most definitely curved to crescent.

This morning (28/8) I got a brief look before low cloud rolled in at sunrise. Phase was 50% - perhaps ever so slighly over to gibbous.

So dichtomy seems to have occured a good 10-12 days or so after greatest elongation. Really happy to have watched this happen

[htj]

Great report. I haven't seen much to Venus lately (not a morning person), but you almost make me want to get up early to see this.

[Matt Scunthorpe]

Im the same as htj, i will wait until Venus becomes a night time object then i can look at it and wonder why it was cloudy when it was transitting the sun!

[michael.h.f.wilkinson]

Nice report. I had a few students try to predict the brightness curve of Venus based on phase (calculated with a solid sphere with simple diffuse reflection), and the distance to earth (size). The results were quite unsatisfactory. The reason for this is that the reflection from the thick atmosphere is far more complicated, and I think this explains the difference in timing of maximum elongation and precise 50% phase. The same effect causes the "annular Venus" images taken just before or after the transit.