Solar and Lunar session, 27th December 2020

[Stu]

I have not done too much observing over the break so far, apart from a view of the conjunction for an hour on 20th December so it was great to be out. As happens surprisingly frequently I had two sessions today, one on the Sun in white light and later on viewing the 94.6% illuminated Moon.

I used my Tak FC100DC mounted on a Vixen GP with dual axis drives for both sessions. For solar white light I use a Baader Coolwedge and Mark IV binoviewers, and then simply replace the wedge with a Baader BBHS mirror diagonal for lunar. Using a simple EQ mount in this way works very well for me; quick to setup and tracking that is accurate enough for steady views at high power without constant nudging. Being able to pan around just using the handset really helps too.

Conditions for solar were not ideal for much of the 30 mins or so I had whilst the sun was positioned in the gap between the trees. Thin cloud passing over led to the seeing being quite poor, like viewing under a stream of running water. However, for about five minutes the cloud cleared and the seeing steadied. During this time, the granulation snapped into view very nicely at around x100 and the active regions showed some pleasing detail, although still far from the best that I’ve seen before. AR12794 is the larger of the ARs on show and petal-like detail was visible in the penumbra. AR12795 is smaller but has an interesting split umbral region, whilst the even smaller nearby spot had a number of smaller pores arcing down from it. Given the length of time we have been without activity, it was great to have something to view today.

Switching to lunar mode later on, the skies were clearer and relatively steady, although showing plenty of wobble at higher powers. At 94.6% illuminated, the disk was pretty bright but still lovely to look at as always. One of my favourite features, Schröter’s Valley was well positioned near the terminator with good illumination. The valley itself showed well, leading away from Herodotus, whilst the crater  Aristarchus had one wall in shadow, and the other brightly lit and showed several dark stripes running down to the crater floor, separating the bright sections.

Other than that, the most notable features I looked at were the ray traces around Kepler and Copernicus which stood out beautifully against the surround mare. As ever, I also picked out the twin craters Messier and Messier A. This time both brightly lit, with the ray trace leading away from them.

So, two short but rewarding sessions on our two nearest neighbours. Great to be out there. Smartphone images added to give a flavour of what was on show, although visually the detail was much better obviously.

[JeremyS]

Nice job 👍🏻 @Stu!

[RobertI]

Nice report Stu. What kind of magnification do you go to with your BV's on the sun? I know you mention granulation at 100x but do you go higher? Funny, I never even considered using my BVs for solar - next thing on the list (when I have sorted the fault I have discovered with the BVs!).

[Stu]

14 hours ago, RobertI said:

Nice report Stu. What kind of magnification do you go to with your BV's on the sun? I know you mention granulation at 100x but do you go higher? Funny, I never even considered using my BVs for solar - next thing on the list (when I have sorted the fault I have discovered with the BVs!).

To be honest Robert, I’m never 100% sure of the maximum magnification I’m using, but I believe that it is around x200.

I use 25mm eyepieces and a x1.7 GPC with an AP Barcon element on front of the binoviewers. I always assume that this gives at least x2 on top of the GPC due to the additional light path up to the eyepieces. This would give 25/(1.7 x 2)=7.35mm equivalent or x100. I then add one or two extension tubes which I assume give me x150 and x200, although I’m sure there are plenty of flaws in my calculations.

Yesterday the conditions didn’t support very high power, so I stuck to x100. When the seeing is excellent the views at x200 are wonderful.