Tuesday, January 23, 2018

Ghostly Galleon

                            The wind was a torrent of darkness among the gusty trees.   
                            The moon was a ghostly galleon tossed upon cloudy seas.   
                            The road was a ribbon of moonlight over the purple moor,   
                            And the highwayman came riding—
                            The highwayman came riding, up to the old inn-door.

                                                                 (The Highwayman, by Alfred Noyes)

Loloma Elementary School, Scottsdale AZ, sometime in the 1960s

In Loloma Elementary School we regularly had to memorize fairly lengthy poems and then recite them to the rest of the class. (I wonder if people still do that today?) One that I can still recall after all these years is Alfred Noyes' 102-line The Highwayman. And the line that I remember best is right at the top - line 2. "The moon was a ghostly galleon." I had no idea what a galleon was, and had to ask. But the power of that line was immediately apparent, even to my 10 year old brain. I absolutely love the sight of a full moon amidst a sky of fast moving patchy clouds. The clouds seem to be standing still, with the moon racing along behind them, ducking from cover to cover. It remains my favorite optical illusion.

As much as I love observing the Moon through a telescope, I have to admit that some of the most incredible views I have had of our planet's satellite have been using nothing but my eyes. When I lived in Fells Point, Baltimore, I would make a point of standing at the water's edge at moonrise and watch it emerge from the harbor. It seemed to positively leap out of the waves, and I could almost feel the Earth rotating beneath me. Just as impressive would be driving (east) home along I-70 from a Carrs Mill star party and seeing the Moon at eye level, especially when it is bright orange as it sometimes appears. And a pencil-thin crescent in the deep blue twilight just after sunset is, I think, one of the most beautiful sights nature has to offer - especially when accompanied by brilliant Venus as the Evening Star.

But one my favorite atmospheric effects is the lunar halo. Caused by the diffraction of moonlight by ice crystals high in the atmosphere, a truly stupendous circle of light surrounds the Moon, dominating the entire sky. At such times I like to imagine myself standing on the surface of Amalthea, the innermost large moon of Jupiter, and staring up at the impossibly large globe of that planet hanging above me. Picture the halo being Jupiter, and you get the idea.

Jupiter, as seen from the surface of Amalthea

Only once in my life have I been privileged to see a moonbow. It's basically a rainbow, as seen by moonlight. All the same colors are there, but muted and somewhat silvery - and, of course, it's nighttime. I was driving home from a day at RAF Waddington in England, passing through one of the all-too-frequent rain showers one experiences on that island, when there it was, off over the fields and above the hedgerows. Pure magic - I half expected to see fairies dancing along the roadside. By chance, I happened to be passing a circle of standing stones, erected some thousands of years ago, and pulled over to drink in the sight (one of the many times I wished I owned a camera).

Through the telescope, the Moon's surface is naturally the star of the show. But it's always a thrill when I see a high flying bat pass in front of lunar disk. The frequency of such fly-bys is absolutely amazing, considering how small an area of the sky the Moon occupies. The air above Carrs Mill must be positively saturated with bats for so many of them to be observed in such a tiny space.

So a word to all you Moon-haters who might be reading this. Don't overlook the many wonderful sights our satellite can offer, even while it drowns out all the fainter deep sky objects out there. There's as much poetry in a moonlit night as there is under the unchallenged stars, and we're lucky to be able to enjoy it.

Saturday, January 20, 2018

A Horse of a Different Color

(Much of the following was originally posted to the now sadly-defunct HAL Forum on 5 May 2013, but it is still quite relevant.)

The winter sky presents us with an embarrassment of riches, but all too often we reflexibly fall back upon the same old warhorses - the Great Nebula in Orion, the Pleiades, the Crab Nebula, or the open clusters of Auriga, etc. But there is more to the sky than what can be found in the Messier Catalog - a lot more. Now most HAL members know that I am a sucker for all double stars, but the ones I enjoy the most are those with a lot of color, especially contrasting color. One of the best is visible right now in the late twilight/early evening sky in Gemini, the magnitude 4.71 star 38 Geminorum. It's an easy star hop to the left of Xi Geminorum, one end of the foot of Pollux (one of the twins, for which the constellation is named). The star is easily found just by scanning the sky about one-third the distance between Gamma Geminorum (the other end of that same foot) and Procyon off over in Canis Minor.

38 Geminorum is located near the center-bottom of this chart.

The first time I laid eyes on this star, I had a difficult time deciding exactly what the colors of its two components were. I felt fairly confident in calling the primary (brighter) component yellow, but the hue of its dimmer companion quite eluded me (it still does!). It almost seemed to change before my eyes from gray to green to dusky red! And it appears I am not alone in this. Just look at some of the descriptions you can find on the web from various observers:

"38 Geminorum is a nice yellow and pale blue pair that may be comfortably split in small telescopes."
"To my eye this star seemed to be a yellow white color with a pale yellow orange companion."
"At 70x I could notice the color contrast of pale yellow and lavender grey"
"Primary is bright white, secondary to faint to tell."
"Primary is a greenish-yellow while secondary is a deeper gold."
"The color of the brighter seemed to be pale white yellow with an orange companion."
"Primary color: White-yellowish - Secondary color: Blue"

What colors do you see?

Friday, January 19, 2018

The Mountains of Eternal Light

Years and years ago, back when I used to know everything, I thought that shadows in a vacuum would be totally, absolutely black, there being no air to "bend" light into the shadowed areas. This misconception was not helped by observing the Moon. The inky blackness of the lunar shadows gave the impression that, were you to be standing in the middle of one of them, you would be unable to see the ground beneath your feet.

I was also led astray by no less than the venerable science fiction author Arthur C. Clarke, whose every word I once took as the Gospel Truth. In his (wonderful) novel, Islands in the Sky, astronauts spacewalking outside a space station would disappear from view whenever they ventured into the shadow of the station, not reappearing until they were once again directly illuminated by the Sun. How Clarke made such a colossal error, I nowadays fail to understand. There would surely be enough reflected light from the surface of the Earth to light up anything in the space station's shadow. And in fact, such is the case.

Astronaut Shane Kimbrough spacewalking in the the shadow of the ISS, plainly visible

In like manner, the shadowed areas on the Moon would be illuminated by Earthlight. This becomes obvious when you realize that you can see the night side of the Moon, even from the Earth, when the Moon is a slender crescent in the evening sky.

Nevertheless, the deep shadows of the taller lunar peaks must be dark indeed - especially near the poles, where the Earth would be just a degree or two above the horizon and shedding very little light indeed onto the floor of craters such as the nearly 3 mile deep Shackleton, which is located directly at 90° South. (There are, in fact, regions of that crater's floor which never receive direct light from either the Sun or the Earth, and which radar observations indicate are sheathed in perpetual ice.)

By contrast, there are portions of that crater's rim which are in perpetual sunlight - they are never in shadow. This was first postulated by the 19th Century lunar mapmakers Beer and Madler. The French astronomer Camille Flammarion gave them the irresistibly poetic name pics de lumière éternelle (The Mountains of Eternal Light). Their existence was positively confirmed by NASA's Clementine spacecraft in 1994. The classic space artist Chesley Bonestell painted a hauntingly beautiful image of them for Willy Ley's 1951 book The Conquest of Space (I have a disintegrating copy in my library - it's on page 76). He pictures them bathed in red light during a total lunar eclipse. Off in the lower right corner, you can just make out the tiny figures of lunar explorers gazing in wonder at the sight. (I unsuccessfully tried to find the painting on the internet, but you'll have to ask me to show it to you in person.)

Well, you too can gaze in wonder at those same mountains - tomorrow evening in fact. Shortly after sunset on 20 January, the Moon will be ideally positioned to spot them, even in a small telescope. Slide your view along the 13 percent illuminated crescent until you get to the southern tip. Just beyond the end of the crescent, you will see a number of disconnected points of light. It's that easy - there they are!

Note the point of light just beyond the edge of the crescent. 
(South is to the top in this image.)
Click on image to get full resolution.

But don't just look at them. Imagine yourself standing at their feet, in an ice-covered landscape so dark that it might as will not be there. And towering miles over your head are the tops of peaks glaringly lit up in direct sunlight. The contrast would be so great that they would likely appear to be floating unsupported in mid-space. Now what a sight that would be!

Thursday, January 18, 2018

How to See the Rosette Nebula

Rosette Nebula

For years, I could not understand why so many of my fellow stargazers claimed to have observed the Rosette Nebula in Monoceros through the eyepiece, while I utterly failed to see the least hint of nebulosity whenever I tried. Frustrating. I kept wondering, "what was I doing wrong?"

Well, last winter I finally discovered the secret, quite by accident. As in all my previous attempts, I centered my field of view (FOV) on NGC 2244, the star cluster at the center of the Rosette (which to my eye always resembled a slightly crooked step ladder). And once again, no nebula. I was about to chalk it up to bad eyesight, when quite by chance I bumped my telescope, causing NGC 2244 to be at the far left edge of my FOV. And then I saw it! There was no mistaking the contrast - the left side of the FOV was decidedly "murkier" than the right. It even had the subtlest of all possible reddish tinges. By contrast, the right side was purest black, with a speckling of stars.

NGC 2244

That's when I realized in a flash where my mistake lay. The Rosette is so large that, by centering on the cluster at its heart, its nebulosity filled the entire FOV. There was nothing to contrast it to. But by placing the cluster at the far left, fully half of my FOV was nebula-free, and allowed me to see the difference.

Since that night I've returned to the Rosette several times, and now that I know the "trick", have never once failed to observe its nebulosity. Our next chance to take in this beautiful sight will be in the second week of February (i.e., just prior to new moon). That is, of course, weather permitting. Maryland is after all, (in)famous for its mid-February snow dumps!

And while you enjoy the sight, marvel at the incredible youth of what you're looking at. NGC 2244 is estimated to be no more than 5 million years old, making it quite the baby. And it is largely made up of incredibly massive stars, the two largest (HD 46223 and HD 46150) weighing in at as much as 60 suns. Such stars don't normally hang around for long, having the habit of going supernova after a few million years. So enjoy them while you can!

Sunday, January 14, 2018


I grew up in Arizona, at a time when there were no streetlights in my home town of Scottsdale. (It was not then the playground of the wealthy that it is today, but rather a decidedly blue collar town dominated by Motorola's defense industries plant where my father worked.) The night sky, even from my backyard, was glorious. I remember well my older brother Richard and I lying in the grass looking up at the Hyades in the winter sky, seeing naked eye as many stars as one can see today only with binoculars. (My eyesight was better back then too.)

Another thing we loved to do was go fishing. There were trout streams to the north, within a day's drive up in the high elevations around Flagstaff. But closer to home were the reservoirs along the Salt River.  The closest was Saguaro Lake. There we'd go out on the boat docks at sunset and fish deep into the night, with the awesome splendour of a truly dark sky overhead, and the utter silence of the nocturnal desert all around - the only sound being our never ending conversation and the almost nonexistent wavelets lapping against the dock.

Saguaro Lake

On one such trip, we fished (and talked) the whole night through. Dawn was approaching but there was still not a hint of it in the sky, when over the dark line of the mountains to the east (visible in the above picture) we were startled by an unbelievable and utterly mysterious sight. What appeared to be a gigantic blue dome was ever so slowly lifting itself into the sky. It seemed almost transparent, and the color was something I had never seen outside a tank full of tropical fish - an electric blue, yet so clear you felt you could see right through it. Imagine an insanely large soap bubble rising into view and you might get something of the idea.

My brother and I had no idea what it could be, and didn't even try to guess. We just watched transfixed as it slowly swelled into a full hemisphere of perfect wonder and absolute mystery. Then, in an instant all became clear. At either side of the blue dome, there appeared 2 unbearably bright points of light that put all into perspective. We had been watching the unlit side of a pencil thin late crescent moon precede the sun in its rising. Before you knew it, the entire crescent was visible. The mystery had disappeared in a flash, but the magic remained. Bathed in Earthlight, the Moon reflected ourselves back to ourselves, and it was beautiful.

Thursday, January 11, 2018

Star of the Month - January 2018

The arctic temperatures and persistent cloud cover of late have perhaps turned my mind of late to more indoor pursuits, but I have hopes for conditions near the end of this month. So it's time to think about which star gets the title role for January before it's too late.  And the winner is...

Eta (η) 24 Cassiopeiae.

Discovered by Sir William Herschel in 1779, Eta Cassiopeiae is one of the loveliest of the wintertime double stars, and I always take a moment or two to take it in when Cassiopeia is high in the sky. Stellar color is notoriously hard to pin down, and no two observers ever seem to see the same thing. I personally see two red stars of unequal brightness when viewing this one, but most observers report the brighter component as being either yellow or gold, with the dimmer companion appearing as anything from orange, red, or even purple.

Eta Cassiopeiae is about 19 and a half light years from our Solar System, and has a combined apparent magnitude of 3.44. The dimmer B component goes round the more massive primary in a highly elongated orbit, closing to 36 AU (for comparison, Neptune orbits our Sun at 30 AU) before swinging out to 106 AU at its furthest point. A single orbit takes 480 years, so we are still less than halfway through a single time round since Herschel first laid eyes on this star. Both components are extremely metal poor, indicating that they may belong to a previous generation of stars than our Sun.

Don't miss this stellar jewel, worthy of the queen which it graces. The image above was the best I could find, but it does not do justice to the reality.