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 Post subject: Mercury
PostPosted: Sat Jun 29, 2019 8:50 pm 
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Joined: Thu Jun 02, 2016 11:32 am
Posts: 424
Location: New Farnley, Leeds lat 53.8N long 1.6W
2019 June 25 0715 UT. 102mm Maksutov x260. Seeing Ant IV - III. Melbourne, Australia.


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 Post subject: Re: Mercury
PostPosted: Sun Jun 30, 2019 6:48 am 
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Joined: Sun May 11, 2008 6:11 pm
Posts: 3219
Location: Portslade, Sussex Lat 50deg 51min Long 0deg 13mins West
Nice one, Bob! Do you know I have never seen a phase on Mercury despite having found it 572 times to date as these have all been observed with low magnification optics. Regards maf


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 Post subject: Re: Mercury
PostPosted: Tue Jul 02, 2019 11:42 am 
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Joined: Thu Jun 02, 2016 11:32 am
Posts: 424
Location: New Farnley, Leeds lat 53.8N long 1.6W
It's an interesting point Mike. On the day I did the sketch I could clearly see the phase of the tiny, tiny image distinctly with x40 in the 102mm maksutov. Previously, I have had no trouble making out various Mercury phases at similar powers with an 80mm refractor. I have no idea what the smallest aperture and magnification would be required; much depends on the apparent size of the disc, the phase displayed and the light level of the foreground sky. I wonder what you would need to make out a disc subtending 8.5 arcsecs and about one third illuminated, in twilight (in other words a thick crescent). 60mm x 30 maybe? Regards, Bob


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 Post subject: Re: Mercury
PostPosted: Tue Jul 02, 2019 3:06 pm 
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Joined: Sun May 11, 2008 6:11 pm
Posts: 3219
Location: Portslade, Sussex Lat 50deg 51min Long 0deg 13mins West
Checking through my Astronomical Diaries from 1990 to 2010, I came across the following observations made from the Foredown Tower with someone else's telescope which are relevant when taking about Mercury's phase.
"March 30/3/2004. Ventured to the Foredown Tower car park with George who wanted to observe Mercury with his new 4-inch refractor. After a long search we eventually located Mercury at 2012hrs, when it was about 8 degrees up. Although it was obviously a planet in the refractor telescope ( added later...Not a starry point!) the precise phase was not discernable. (added later... the magnifications used were not recorded.)"
That was the best I can say I have ever seen it.
Similarly, I came across another observation, not about Mercury but seeing details on Mars and disc of Uranus.
"Observing Session with 6" Reflector (x50 & x140) at Foredown Tower. Midnight of 22/23 August 2003 with George H. Initially observed Mars and one of two bands of dark markings were visible but the most obvious feature was the polar cap. Uranus was clearly seen as a tiny disc.........."
I have rarely seen details on Mars or seen Uranus as a disc. Come to think of it, I have never seen the Jovian Red Spot either! Regards maf


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