President’s Message – Dec 2021

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Ah 2021. What a strange trip around the Sun! I am writing this letter on the day of the winter solstice. There is a waning gibbous moon shining high in the east, when I go to bed, and it is high in the west to greet me in the morning. I take great solace in watching and thinking about the dependable motion of the Earth through the Universe, while so much of life and news this year has left me feeling unsettled.

Randy Enkin using his sextant
Randy Enkin using his sextant

Nearly as dependable as the astronomical objects has been you, our astronomical community. I am so pleased when I see the 30 or 40 of us gather each Monday evening at our virtual Astro Café. We are an appreciative and supportive community. Look at all the different skill sets and experiences that get shared every week. And look at those beautiful photos and sketches that we have created. I particularly wish to mention the personal observatories (I know of 3!) that are getting designed and built by members of our centre, as well as the fantastic work by our technical committee in upgrading the Victoria Centre Observatory.

Our group has motivated me to try new astro-projects – whether observing sunspots with a solar telescope borrowed from the Centre (thanks to the capable curation of our telescope collection by Sid Sidhu), or star hopping to those faint fuzzies that you deep space observers like. And I love the expressions of appreciation when I show off my lunar sketches to our crowd.

Do remember that our community survives on the strength of our volunteerism. We have a specific requirement this year for a new secretary and a new vice president. Don’t feel you aren’t up to the job! I still feel like a newbie in the role of president, but there is no shortage of good council from the many past executives who continue to be active. Come join us on the inside, and you will feel even more affection for the Centre.

I wish us all a fruitful and fulfilling new year, with many clear skies.

Look Up,
Randy Enkin, President@Victoria.RASC.ca

President’s Message – Nov 2021

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Everybody should have a good astro-project on the go. My current one concerns the timing of lunar eclipses.

Solar eclipse geography and timing is known with remarkable precision. So much so that people, including many members of our RASC community, are willing to plan long, difficult, and expensive trips to watch them. The timing and location of the earth’s shadow, or umbra, across the Moon during a lunar eclipse is much more variable and poorly understood.

I was delighted to learn that as far back as 1687, Philippe de la Hire published that the Earth’s shadow was larger than could be accounted for by an airless Earth, leading to lunar eclipses that start a few minutes earlier and end a few minutes later than expected. This was important work, because observing the timing of eclipses was, in principle, one way to measure longitude – as long as the expected timing was well established.

Moon on Dallas Road, Oct 8, 2021, by Randy Enkin

The problem arises from the complex nature of the earth’s atmosphere that obscures, diffracts and refracts the sun’s light on its way to the Moon. I first became aware of the role of amateur lunar crater eclipse timing just before the eclipse last May (which was clouded out), and I am certainly keen to try again on the upcoming lunar eclipse, starting around 23:19 PST on Thursday, November 18. If there are clear skies, I’ll be out with my telescope, noting the time to the tenth of a minute that the earth’s umbra darkens (“immersion”) and then departs (“emersion”) from various lunar craters. Sky and Telescope has been compiling these observations since 1956. Herald and Sinnott (2014) have analysed the compilation, extended back to 1842, with an amazing 22 539 observations. Their main conclusion is that the Earth is surrounded by a “notional eclipse-forming layer” that is 87km thick. It is a really surprising result, since even noctilucent clouds don’t show up that high in the atmosphere.

Herald and Sinnott point out that amateur uninstrumented observations provide continuity with the early observations in their compilation and provide insight into the visual response of the human eye. To help with the observations, Thursday- Friday November 18-19, I have annotated a picture of the full moon with the crater timings predicted by Fred Espenak. I hope some of you will join me making these simple but useful observations.

Look Up,
Randy Enkin, President@Victoria.RASC.ca

President’s Message – October 2021

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Questions, Answers, and Questions

Randy Enkin using his sextant
Randy Enkin using his sextant

One satisfaction of astronomy is the sense of continuity with astronomers from all over the world and spanning the decades, centuries, and millennia. The wonders of the sky fill us with awe and provoke so many questions. I appreciate the multidisciplinary approach to answering these questions.

Today’s anecdote concerns an article published this week, with 25 authors from 5 countries. The Chinese Chang’e 5 probe brought back to Earth the first lunar samples in 4 decades. They targeted a place on the Moon that was suspected of being young, due to the region’s low density of craters. Galileo observed craters on the moon 400 years ago, but it was only in the 1960s that meteor impacts were confirmed to be the dominant mechanism of their origin.

The observational and theoretical development of celestial mechanics, universal gravitation, the solar nebula, and planetary accretion were all required to understand dating planetary surfaces, by measuring the size and number of craters. We also needed telescopes, rockets, robotics, petrology, geochemistry, and geochronology to complement the study. The Moon is the only planetary body where impact crater ages have been calibrated with radiometric dating, but there had been no samples so far measured that are between 3.2 and 0.8 billion years old. The new samples were dated at 1.96±.06 billion years, sitting in the middle of that gap and forcing a revision of the current crater dating method. The new date is very young for the Moon’s surface and brings up new questions, like why the Moon was still melting crust so recently.

Back-scattered electron (BSE) images and false color energy dispersive spectroscopy (EDS) element maps of the two fragments from the Chang’e 5 sample
Back-scattered electron (BSE) images and false color energy dispersive spectroscopy (EDS) element maps of the two fragments from the Chang’e 5 sample

I’m filled with a sense of connection with my fellow humans who can conceive of such questions, work on them from many different aspects over the centuries, answer some, and end up with even more questions. And I look up at the sky with happiness.

Look Up,
Randy Enkin email