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By Jupiter!

A blog about the stars, astronomy gifts, and other starry musings by the folks behind Indigo Night.

Celestial Mechanics

by Van Wymelenberg
October 21, 2009
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I thought I’d take some time over the next few posts to give you some sources and links I’ve found especially useful as introductions to the science of the night sky. When people call to place an order, I’m often asked, with some incredulity, how on earth (love that expression) we can figure out what the sky looked like way back in [insert date here]. Speculation often goes to "do you have a vast archives of photographs? (admittedly, our prints do look photo-realistic, so I suppose this is understandable on some level), or (the most interesting take, in my opinion) to “using Hubble to ‘look back in time.’” Interesting concepts both, but no.

Observational Astronomy is rooted in Celestial Mechanics – the branch of astronomy that explores the slow dance of our moon and planets wandering in procession against the vast canopy of night – those million, million fixed points of light, the stars in our night sky. ‘Planet’ actually comes to us from the Greek, planetai, literally wandering.

The science behind what we do here has been worked out for hundreds of years, though until recently it’s been the exclusive domain of the mathematician/astronomer. Formulas for calculating the orbits of planets go all the way back to Galileo and Kepler in the 1600s.

Let’s start here with that list of resources. Stellarium is free, open source planetarium software for the PC, MAC and LINUX operating system. Seriously cool.

Stellarium is like the software that we use here at Indigo Night. I can’t believe it’s free… it’s really a remarkable piece of work. This will put a virtual planetarium on your desktop. The controls are very simple and intuitive. Elegant. Pick a location, key in a date and time, and there’s the sky. It will give you a horizon line with illustration and compass point to orient yourself, unlike many internet astronomy references that bear no relation to what you see when you look to the sky… at least at first glance. Click and drag to rotate your view.

You can go back and look at the sky on the day you were born, or when your child was born. The night you fell in love. The night you married. And, of course, it’s predictive. That’s how most star-gazers use a program like this: to plan an observation session. What will be visible in the sky tonight? Will Saturn stand above the treetops at nightfall? For the naked eye observer new to the night sky, on the other hand, it tends to be used more as a real-time chart, or legend, of the sky. It answers the question “What’s that bright object low in the southeast at nightfall?” A UFO? Or perhaps Venus?

Play with the date. You’ll see that each year, on a given date at a given hour, the stars are, for all intents and purposes, in the same place. If you look out the window of your grandfather’s upstairs bedroom on say, November 4 of 2009 at 11 PM, you’ll see very nearly the same star filled sky that your grandfather saw at 11 PM on November 4th of 1939.

Now, the moon and planets will be different –– that’s the part I find so interesting. The great clockwork of our night sky. Each planet orbits the sun in it’s own sweet time – earth in one year, obviously. Saturn takes about 30 years. Jupiter about 12, moving through roughly one sign of the zodiac each year. Venus takes about 7 months, moving from ‘Morning Star’ to ‘Evening Star’ and back, as its orbit takes it behind (or in front of) the sun, lost from view to us for several months, then back out into the night sky.

These infinite variations in the pattern of the night sky, this regal dance in the heavens, slow, majestic, and absolutely, steadfastly, correct… that’s the beauty of it, to me, connecting all of us, across cultures and time. We all share a common frame of reference, our small blue-green planet, this island earth. Enjoy the view.

Blue Moon

by Van Wymelenberg
October 09, 2009
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OK, Just a couple of more things on blue moon. “Once in a blue moon,” meaning rarely, has been a well known idiomatic expression since the mid to late 19th century. It’s original meaning of ‘never’ somehow morphed in ‘rarely.’ One possible explanation points to the natural philosopher. The 1800s were a time when science started to answer questions about the physical world, and that knowledge made its way to the public through increasingly easier access to newspaper and books. Common knowledge changes language.

One notable event that naturalists studied and reported on was the eruption of Krakatoa, an Indonesian volcano in the Sundra Straits, near Java. The cataclysmic eruption, late August of 1883, killed somewhere between 36,000 (official toll) and 120,000 people. A massive plume of ash was ejected into the atmosphere. Dark times, indeed. Average global temperatures fell 2.5° F the following year. There were widespread reports of ‘green’ sunsets and ‘blue’ moons over the next several years. And what’s that about? Particulate matter of about one micrometer (as from this eruption) suspended high in the atmosphere will filter out red light, and pass blue. Thus, the blue moon. The same effect has been observed following large forest fires.

I think I’ll let the blue moon thing rest for now, although I reserve the right to look at the 1934 Rogers and Hart lyrics to ‘Blue Moon.’ As well as the subsequent Elvis interpretation. And to report back on a certain Belgian Style beer.

Belewe Moon

by Van Wymelenberg
September 29, 2009
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Two full moons will grace the December sky this year. This happens occasionally: most months have 30 or 31 days. The lunar month – the time it takes the moon to orbit the earth (also known as the lunation or its synodic cycle) – is 29 days, 12 hours, 44 minutes and 2.78 seconds. This time difference between the lunar month and the calendar month causes the two cycles to slowly weave in and out of sync. Every once in a while the synodic cycle of the moon falls completely within a calendar month, and two full moons appear in that given month. This happens about once every two or three years. The second full moon in a calendar month is commonly known as a ‘Blue Moon.’

This popular consensus on the astronomical meaning of a ‘Blue Moon’ is recent, only really finding it’s way into our language within the past 30 years or so.

The back story on the expression ‘Blue Moon’ is wonderfully complicated. Old English scholars point to the possible double meaning of ‘belewe’ in the earliest reference to ‘Blue Moon,’ which appeared in a short pamphlet entitled Rede Me and Be Not Wrothe. This short work was published in 1528. It was, to my understanding, a kind of critical essay mocking the English Clergy. The exact line is:

If they say the moon is blue / We must believe that it is true.

The word ‘belewe’ had a double meaning in Old English. It could have meant either the color blue, or ‘to betray.’

I think the writer was a man of wit, working ‘belewe’ here as a clever double-entendre, and perhaps introducing the idiomatic expression ‘blue moon’ for the first time. Although the meaning was clearly different then.

Here is the backstory. The church was the keeper of all arcane knowledge in those dark times, including the calculation for the date of Easter.

The date for Easter was (is) based on the date of a particular full moon. Easter must fall on the Sunday following the first full moon after the ecclesiastical vernal equinox, which always falls on March 21. (The Church divided the year neatly into 4 seasons, each of exactly 3 month, with the equinoxes and solstices always falling on the 21st. Astronomers, however, always define the change of seasons as when the sun crosses the celestial equator, or when it reaches it’s northernmost or southernmost extreme.)

Many important Christian days, such as Saint days, are fixed on the calendar, always on the same date, but Easter is variable because of the holy day’s origin during early Christianity’s Jewish Period. It referenced the Jewish lunisolar calendar, as did many other important events. The tradition of doing the calculation rather than fixing the date was kept by the Christians as its dogma evolved from Judaism.)

It’s a little too complicated, and off subject, to go into it here, but the calculations are kind of interesting and you can look at them here).

The short version of the story is that the church had to say which moon was the Lenten Moon, and which was the Paschal (Easter) Moon, because it wasn’t always obvious. Seven times over the course of every 19 years there would an extra moon somewhere in a season.

The three full moons across each “normal” season all had well established names that helped people organize their lives. The moons marked the change of seasons, and told them when to plant, reap, fast, celebrate, be hopeful. To everything there is a season as it is so beautifully written in the book of Ecclesiastes. But the ‘belewe’ moon betrayed this celestial almanac. Since there was no regular name for this moon, because it appeared in different seasons, those who kept the names and the knowledge would call this third full moon in a season of four moons the ‘belewe’ moon. The fist, second and last moon of a season kept their traditional names, and the rhythm of the seasons remained intact.

I’m no Old English scholar (or even student) but it seems to me that this early pamphlet confirms that the everyday use of the phrase ‘belewe moon’ was the liturgical reference to the third full moon in a season of four full moons. And that the ironic use of ‘belewe moon,’ meaning something that is absurd or impossible, was also indicated, perhaps for the first time, here in this same short work. Why else would the author speak thus? He was already being critical of the clergy, so there was obviously no fear involved, no need to cleverly mask the meaning in double-entendre. I call it wit. We’ll never know for sure.

This ecclisiastical definition of a ‘blue moon’ is followed by the Maine Farmer’s Almanac and is noted in publications as far back at 1817. This ‘rule’ is now generally referred to as the ‘Maine rule.’

And there’s more! Due to a misinterpretation of a 1943 Sky & Telescope article about the Maine Rule, a second definition of “blue moon” entered the vernacular. In an understandable mis-reading of this article an author simplified the rule to define a blue moon as the second full moon in any given month. One of the Stardate editors picked up on this definition from Sky&Telescope (hey, if you can’t trust S&T who can you trust?) and further popularized it in national radio broadcasts sometime in the late 1970s. The error has been noted by both Stardate and S&T, but the definition is so much a part of popular culture now it’s even made its way into Trivial Pursuit. But maybe not the genius edition.

A favorite passage remembered

by Van Wymelenberg
August 31, 2009
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The Wind In The Willows by Kenneth Grahame has long been treasured friend, one that always delights and comforts me. My copy has the wonderful line drawings by Ernest Shepard. I won it in a book character contest one summer in my 11th year at our neighborhood library. I took top honors with my stunning and subtly nuanced interpretation of Mark Twain. As I recall I was up against quite a few Davie Crocketts and Daniel Boones, coonskin caps being all the rage that year.

I read the book every 5 years or so. The last time I read it I paid particular attention to Mr Grahame’s descriptions of the night sky. I do this with all the fiction I read now, kind of in the ‘fact-checker’ mode. (In the nautical fiction of Patrick O’Brian, especially: he has some exquisite passages about sailing at night under a vast cathedral of stars.)

In Chapter Seven of Wind In The Willows, The Piper At The Gates Of Dawn, Rat and Mole assist their friend Otter in looking for Otter’s son, Portly, who had gone missing, but not to panic or worry, Portly was always straying off and getting lost… except this time was a bit more serious, he had been missing for several days in the Wild Wood. Rat and Mole decided to continue the daytime search through the coming night, concentrating along the river.

Though it was past ten o’clock at night, the sky still clung to and retained some lingering skirts of light from the departed day; and the sullen heats of the torrid afternoon broke up and rolled away at the dispersing touch of the cool fingers of the short midsummer night.

Knowing that the Wild Wood is based, approximately, on the the area surrounding village of Lerryn, in Cornwall. And that Midsummer is the generally the time around the solstice; and (from a later conversation in which Rat mentions the fact) that moonrise was near midnight that night…

I look through the ephemeris for 50° 23’ N and 4° 37’ W on 21 June of various years, searching for a moonrise at midnight. On 20 June, 1900 I found a last quarter moon rising at 11:56 PM. That would work. 20 June of 1903 shows a waning crescent, about 32% illuminated, rising about 1:09 AM. That fits too. There was no Summer Time (or Daylight Savings Time as we say here in the states) when Mr Grahame was writing this book — that didn’t come into effect for another 10 years of so. The book was published in 1908, so I figure this was about the right time frame.

Mr Grahame describes nautical twilight – a time when horizon features are still faintly visible, but the darkening sky will offer up a few bright stars if you know where to look; and some lightness west, perhaps some high whispy clouds lit by the sun, now below the horizon. When Grahame describes his lingering skirts of light perhaps he was referring to noctilucent clouds: a high altitude cloud that is luminous at twilight at higher latitudes, such as Cornwall, near 50° North. (I’ll post on NLCs soon – uncommonly beautiful.) Nautical twilight occurs, technically, when the center of the sun is 12° below the horizon. This is when navigators locked their legs about the lower shrouds, took sextant and chronometer in hand, and determined the altitude of a particular star above the horizon. In order to plot a ship’s position.

So the first general description of night holds true: the sun was about 10.5° below the horizon at 10 PM local time, at Midsummer, in the Wild Wood, by my calculations. The last vestige of twilight would be showing west. And about the rising moon, east, toward midnight:

The line of the horizon was clear and hard against the sky, and in one particular quarter it showed black against a silvery climbing phosphorescence that grew and grew. At last, over the rim of the waiting earth the moon lifted with slow majesty till it swung clear of the horizon and rode off, free of moorings; and once more they began to see surfaces—meadows widespread, and quiet gardens, and the river itself from bank to bank, all softly disclosed, and washed clean of mystery and terror, all radiant again as by day, but with a difference that was tremendous.

I love that moonrise. I see it. It’s so true how the world is ‘softly disclosed’ by moonlight, even the light of a waning crescent moon. That is actually enough light to read by. I’ve done it.

The story continues with Rat and Mole working upstream slowly until sometime near morning twilight. He relates that

… the moon, serene and detached in a cloudless sky, did what she could, though so far off, to help them in their quest; till her hour came and she sank earthwards reluctantly, and left them, and mystery once more held field and river.

He doesn’t say the moon set but that it sank earthward reluctantly, and left them.

I believe Rat and Mole may have been on the south shore of the river, up against a tall stand of English Oak, because this type of moon would not set until well after daylight. But it could have disappeared behind the trees, certainly. (And reluctantly.)

The waning crescent moon, the moon that rises in the east at midnight, would not transit, or cross, the south meridian until the following morning, and would not set until early afternoon. Technically it is rising until it transits. Even at dawn the moon would not be sinking earthward. Except near Toad Hall. I’ll tell you though, in my experience as a walker in the woods at night, it’s all a trick of perspective. You walk down a path and the moon is well above the horizon. You work your way up a small rise, around a bend, and it’s back at the horizon, bigger, brighter, a different moon altogether. Clearly in the Wild Wood, the perspective is perfectly realized in service of a story well told. I’m sure that’s just the way it was that night.

Rat and Mole did eventually find Portly,by the way, with the help of Pan, the Piper At The Gates Of Dawn.

The Sky Tonight — Week of August 23

by Van Wymelenberg
August 20, 2009
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The moon was new on the 20th so this week we’ll begin to see the barely visible waxing crescent moon low in the west after sundown. On Sunday, the 23rd, look for the crescent moon, about 17% illuminated, and the bright star Spica, lucida (brightest star in a given constellation) of Virgo. Look toward the horizon, and a little west and you may see Saturn, and possibly Mercury, especially if you are viewing with binoculars.

After moonset, in the deepening twilight, brilliant Jupiter will show rising southeast in faint Capricornus. At the meridian, majestic Scorpius, the celestial Scorpion. Each day this week the moon rises later, and of course sets later, and more of the illuminated portion of the disk is revealed. First quarter is on the 26th. By Thursday, the 27th, the moon with be in Scorpius. Antares, the bright heart of Scorpius – a ruddy colored star, often mistaken for Mars – will show close, just to the right of the moon, now in it’s gibbous phase (gibbous: more than half illuminated, still waxing toward full.)

Next week the moon has a close encounter with Jupiter.

I love looking at the moon. Most star-gazers disdain the inconstant moon… yes, of course, it’s light steals the beauty of the night sky, of the indigo night, quoting the poem that gave us a name. But it’s just so beautiful. We forget. When I take the time to really look at the moon I still get that childish delight and amazement, that quickening, especially when I see the rise or set against a landscape or seascape. A brief meditation, and the flat disk, pie plate in the sky moon emerges as a sphere, it’s beautiful roundness an affirmation in satellite of our own world.

This is especially true with Earthshine. This is when the dark portion of a thin crescent moon is dimly lit by light reflected from earth — primarily clouds. This happens mostly when the moon is new, or near new, and stands between the earth and the sun. Here, the full face of the earth reflects light onto the moon – much more so than if the moon is off to the side or opposite the sun, at first quarter, full and or last quarter. All this reflected light falls on the dark side of the moon, filling the inky black shadow with soft light, a low level luminous haze. Texture emerges. The dark outer edge gains in definition, and it’s easier to see the moon as a sphere. The reflected light adds to the direct light that falls on the crescent arc as well, and in photographs you’ll see this as a beautiful radiant glow, just off the scale.

Earthshine, or the new moon in the old moon’s arms usually visible in twilight when the moon is in it’s crescent phase.

[This photograph is by Ilmari Karoned. It was taken in Helsinki on 21 July 2006. Used with permission under a Creative Commons license]. And I’ll leave you with this, for no particular reason: They dined on mince, and slices of quince, which they ate with a runcible spoon; and hand in hand, on the edge of the sand, they danced by the light of the moon, the moon, they danced by the light of the moon. E Lear.

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Just Because

The night sky print which arrives for no particular reason, other than to celebrate the gift of love that is your beloved, is cherished like no other.

Birthdays

Each of us has a story that begins in a single moment. Poets and philosophers from Shakespeare to Tennyson, from Moore to Jung, share a common fascination with the night sky at the moment of birth, and the idea that the moon and stars stand in timeless, silent witness to this moment.

Wedding Anniversaries

The night sky print, showing the moon and stars just as they appeared on the night you met, the moment of your first kiss, or your wedding night, is an exceptional anniversary gift. Appropriate for any year, especially so for the 1st anniversary, the year of the ‘paper’ gift.

New Baby

The night sky print, showing the moon and stars just as they appeared on the child’s first starry night, with your words – funny, wise, sweet, hopeful, perhaps a favorite quote from a story or song – makes a beautiful keepsake.

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