4.08.2024 I don't believe it! H-a observing?

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  Sunday 4th. I can hardly believe it! Early thunder and rain, then brief sunshine. Now there was the threat of a very large sunspot. 

 This drove me to collect the various bits of my Lunt LS60MT together into a useful bundle. The H-alpha parts had been greatly extended and attached to the 6" up in the observatory. So had become separated from the objective and its stubby main tube. Once assembled indoors I plopped it onto the Manfrotto tripod,. Then dragged it outside and waited. And waited. Heavy clouds blocked most of the sky.  

 Finally, I had my first view of the H-alpha sun in a very long time.  

 12.00 I upped the power progressively. Until a no-name, 10mm Plossl provided a nicely crisp image at a nominal 45x. I added a TS 1.25" star diagonal for lots more comfort. The sun was high in the SE and my neck had been complaining. No matter how I adjusted the tripod up and down. 

 The multiple splodges of the scattered sunspots were clearly visible. The large spot, coming around the advancing limb, seemed less dramatic. Now it had cleared the limb. Meanwhile, blue holes had steadily increased in the heavy cloud cover.

 12.40 Brief sunny periods at the moment. The afternoon forecast looks much more promising. I'll have lunch and then go back out again.

 14.00 Heavy overcast! All afternoon!

 Sitting on a patio chair on the open lawn and viewing the sun reminded me of two things. There is "dome seeing." From the observatory heating up in the sunshine and causing thermal currents in the air. There is also dome shelter. Which protects the observer/imager from direct sunlight and the wind. And rain of course. Though the latter usually results in closing the shutter(s.) Taking only a few moments compared with rushing indoors with armfuls of equipment. 

 This is the most telling reason for having an observatory. There are others of course. No need for polar alignment providing one has a permanent pier and an equatorial mounting with a memory. Starting up and switching off afterwards should be reduced to a minor irritation. Instead of a complete workout.

 Reading back though my past blog posts. Confirms that I really struggled with highly variable seeing conditions. The plywood dome cladding was certainly a great, solar heat absorber. I had tried draping white tarpaulins. To block the sun. Though with only very limited success. 

 This infra red image is from the other day in bright sunshine. The cool contrast of the vegetation. Compared to the bare plywood of my observatory and shed is truly remarkable. Even the sparse grass in the foreground keeps the ground cool. 

 Just beyond this is the bare gravel. Which is much warmer. Locating a solar observatory looking out over grass makes obvious sense. In reducing local convection currents in the long light path from the sun.  

 Note how cool is the shiny, aluminium tripod ladder. Suggesting a shiny aluminium dome would be much cooler than a plywood one. I shall have to find some white GRP somewhere to photograph with the infra red camera.

[Image from my One+ phone fitted with a USB-C, plug-in, Topdon TC001 infra red camera attachment.]

 Larger apertures are increasingly susceptible to poor seeing conditions. No doubt white paint would have helped. At that time I was against painting the observatory white. It stood out like a sore thumb from the distant road. I didn't want to attract attention.

 A dome is fairly good at protecting large telescopes from the wind. Depending heavily on the wind's direction and the position of the sun in the sky. There were many times I had to dress warmly to cope with a whirlwind in the dome. Despite my massive mounting the telescopes still shook in the wind. Mostly due to end float on the flimsy and badly designed, commercial worm housings. 

 Forum members have expressed doubts. About the wind resistance of the Ioptron CEM120 mounting. This has spring loaded worms but only 216mm [8.5"] worm-wheels. The CEM120 can certainly carry heavy weights. Though its exact design details. Might limit its use in very exposed circumstances. 

 If I should decide to invest in this mounting I should seriously consider its protection in use. I cannot see it performing well out in the open. My front garden is subject to the SW prevailing wind. The raised observatory was rather more fortunate. Due to the shelter provided by all the trees to the west and southwest. The front garden is unprotected beyond the head high, beech hedge. Plus the shrubs I have allowed to grow almost out of control. Mainly to provide interest through the kitchen window and to shelter the greenhouse.

 

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