Xmas Mercury Rising

Discussion on planetary observations

Xmas Mercury Rising

Postby Nightspore » Sun Dec 16, 2018 8:56 pm

I couldn't resist observing a very bright Venus with my Orion 90mm StarMax at around 06:00 GMT. The seeing and transparency seemed above average for the time of year and I could easily see quite a few stars. The Venusian phase was readily apparent at 50x, 69x, 89x, 100x and 125x. I used two plane polarising filters (diagonal & eyepiece).

I watched Venus steadily for about half an hour when with my naked eye I noticed an orange-pink blob low in the plane of the ecliptic. I knew Mercury was in this vicinity. For a moment I wondered if it was an aeroplane but then realised, with great anticipation and excitement, it was indeed the elusive Mercury! At 50x (25mm BST StarGuider) and a single polarising filter I strained to see the phase. Just over 65% is illuminated at a visual magnitude of -0.4. At this low altitude (barely 3 ~ 4°) Mercury was bubbling away in the atmosphere (Antoniadi III ~ IV?).

As it rose higher the 'bubbling' settled slightly enabling me to up the magnification to around a hundred (167x for a brief period) although most of the session was at 89x with a 60° Bresser 'Plossl'. The phase did become more distinct but I could also see a very bright white area that seemed to be in the Apollonia region. I believe this is an albedo feature. It certainly contrasted the dark orange colour of the planet. I observed Mercury until about 07:00 when by this time the dawn sky had bleached all colour out of it.

I'd tried and failed to see Mercury during evening twilight sessions in the spring. I knew there was a chance of seeing it this morning but it all depended on the weather, just like during spring. Due to inclement conditions I missed the dichotomy on the 11th and yesterday's greatest elongation west. So I'm double happy to catch it this morning. This was certainly a nice early Christmas present.

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