Lunar highlights

Previously most of my lunar observing had been limited to the spectacular array of impact craters. Yet most of these contain details that passed me by until I was told to really look, and they only scratch the surface (so to speak) of what the Moon has to offer. Now I’ve surveyed 90% of the sights listed in the Lunar 100 list, what were the highlights?

Discovering Lunar domes and dark halo craters has lead me to consider lunar vulcanism more closely. The latter were completely new to me despite being easily visible under bright illumination. These are long extinct volcanoes or vents and probably a result of the impacts in the early life of the Moon.

Which leads me to the lunar rilles (rimae). I love trying to resolve those thins dark or bright lines, depending on the direction of the sunlight. They’re a real observing challenge though they range enormously in both complexity and size, some being much more easily spotted than others. Faults lines or collapsed lava tubes? They have different origins to investigate.

Likewise I’ve developed quite a soft spot for crater chains (catenae). The Davy Crater Chain is listed amongst the 100, but I’d never noticed it before attempting the list. I’ve discovered that there are several more of these structures which are the result of the Earth tearing a passing asteroid or comet apart. Remember Shoemaker/Levy? That’s what we’re talking about, albeit on a smaller scale.

This is the small scale detail so far and as much as I love this the Moon isn’t the Moon without those vast impact basins that for the Maria. They’re not hard to see, even with the naked eye they’re obvious, so what’s to learn?

Firstly I certainly know where to find more impact basins than before. I also enjoy trying to trace the multiple rings of mountains (I think of them as ripples) around many of them. The area around the Mare Vaporum is a favourite now because of its variety. Evidence of volcanism and the deep scouring by debris from the Imbrim impact, one of the biggest, is really obvious.

With a telescope and the right illumination the Imbrium lavas are covered in dorsa (wrinkle ridges). Initially I thought these were evidence of cooling lava flows. By working out the direction of slope as the illumination changed I hoped I could trace their origin. But I couldn’t because these are genuine ridges and not sloping ways from any centre. This is what happens when the marial lava cools and the impact basin sinks under its weight: the surface really wrinkles! The detail at modest magnification can be impressive, especially since it all disappears when the Sun is high.

This project started out as another observing list to tick off, but I’ve come to realise that misses the point of the Lunar 100. To get the most out of it you have to observe the features and then think about what they’re telling you about the geology and history of the Moon. More than any previous casual sessions, this project has lead me to identify features from continuing observation and research. I have a far better feel for the complexity of our nearest celestial neighbour.

A Feast of Astronomical Observing

And now I’ve forgotten to post through March… which is a shame because it was a huge improvement over February. Not only a big uptick in the quantity of observing opportunities, but lots of variety in my observing diet too.

Both this month and the last have started with some Lunar observing. I’m starting to take this increasingly seriously just as the Moon is due to sink lower in my sky until it disappears behind the house until Autumn… still you have to start sometime, and I’ve decided now with the Charles Wood’s Lunar 100.

Which is why I’m very happy to welcome the return of solar observing. As the Moon sinks, the Sun is getting higher in our northern hemisphere skies, so it’s around now that I start to swap lunar for solar observing. Despite being around solar minimum, with relatively few sunspots to be seen, I’ve been rewarded with some Hα fireworks and spectacular white light sunspots in the last few weeks. Few in number perhaps, but the quality was undiminished.

Planetary observing wasn’t left out as I followed the sliver of Venus up to the last possible moment. For me that was the point it fell behind the houses and trees to the west at sunset on 15 March 2017, but it was a very thin crescent by then: I estimated 5% and Stellarium claims 4.4% illumination. I’ve caught a glimpse of Mercury at sunset too.

There were several Jovian sessions, even though it’s a bit too low to see well from my back garden. I can observe Jupiter low to the SE over the top of my garage for about 30 minutes before it goes behind the house. No moon transits yet, but a look at a slightly washed out Great Red Spot (GRS) was possible in my 60mm refractor. Why the small scope? To have any view I have to pick my position carefully, and you try manhandling a large telescope into the garden undergrowth.

I’ve tried to spot the comets 45P/Honda and C/2015 V2 (Johnson) with my binoculars, but with no success. At first they were too faint or low, then the Moon arrived and I haven’t bothered again. Once the Moon disappears I’ll certainly try again for the latter of the two at least.

March witnessed the arrival of British Summer Time (BST) which heralds the rapid shortening of night in these parts. Naturally in astronomical circles this is never well received, and Deep-Sky observing isn’t going to be easy! By the end of May there’s no astronomical darkness for a couple of months, but in the meantime there can be some lovely transparent skies for the patient.

After a rather wet period in the middle of March, during which the Moon got out of the way, clear skies returned just before BST inflicted itself upon us. I’ve started working on the Herschel 400 list again. This spread of several nights gave me the chance to start on the faint and fuzzy galaxies of Spring, as well as polishing off some surprisingly faint open clusters from late Winter.

Finally, I’ve collected a few more variable star observations thus clearing the backlog a bit and responding to an AAVSO alert on AG Dra (one I regularly follow). The conditions haven’t been great for it: patchy cloud doesn’t kill a lunar session, but it makes reliable binocular variable estimates pretty tricky. Still it’s nice to be logging some data again.

So a March was a much better month and April has started in stunning style with observing sessions on each of the first seven days!

An Unexpected Moon

It was the 8th January 2017. The morning had been lovely with sunshine in place of the predicted fog! It didn’t last. As the afternoon wore on the clouds gathered and by nightfall not only covered the sky but had delivered a persistent drizzle.

So I didn’t expect much when I stuck my head out of the back door at around 22:20 UT. The first thing that struck me was how warm (6°C) it felt despite being dressed in a T-shirt and lightweight fleece pullover. Then I noticed how damp it felt: our local humidity was nearing 100% it seems.

Not expecting much I looked up to the south west and I noticed something bright. The Moon was punching through the rapidly moving clouds well enough to be quite observable!

The Moon at 10.7 days into its lunation
The Moon at 10.7 days into its lunation in Virtual Moon Atlas
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