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 well 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!

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!

Earthlight

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.

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.

Creator of the Stars of Night

A gift to all, this Advent Season:

https://www.youtube.com/watch?v=vIa4cxSnHuM

(Start at one minute in, to avoid the intro.)

In the midst of debates over which telescope is the "best", or exactly how the eye perceives objects through the eyepiece, it's all too easy to lose sight of the fact that...

THE UNIVERSE IS BEAUTIFUL!

And if Latin's not your thing, here's the same song in English:

https://www.youtube.com/watch?v=wIo6LvNkE18

Explorers! (part 2)

There are so many adjectives appropriate to describing deep sky objects: beautiful, awe-inspiring, spectacular - just to name a few. But one word you will not often find on that list would be dramatic. For something to be dramatic, there has to be something actually going on. And for the most part, what we see beyond the confines of our Solar System has all the trappings of eternity. Other than the occasional supernova, nothing happens that is discernable to the human eye - at least, nothing notable over the lifespan of any single individual. With rare exception, what you observe tonight looks pretty much the same as it did 500 years ago, and will remain unchanged for the next 500. And that's actually part of its charm. There's a comfort in the Unchanging Heavens, in their timelessness, in knowing that the ancient Babylonians were observing the same sights as ourselves, as will be our unknowable descendants.

Not so with the Moon. Oh, I know, "Nothing ever happens on the Moon".* It looks the same now as it did millions of years ago. The footprints of American astronauts will still be there ages after the very name of America has been long forgotten. Yes, in that sense, nothing does happen on the Moon. But in another sense, it is forever constantly changing - day by day, hour by hour, minute by minute. I am referring to its appearance to an Earthbound observer. The relentless, inexorable movement of the terminator from east to west with its attendant shadows creates a landscape of ever shifting contour. That lonely mountain with its truly spectacular miles-long isosceles triangle of a shadow will soften to a hard-to-detect whitish smudge over the course of an evening. A line of isolated points of light will emerge as the colossal rim of a crater while you watch. That deep well of purest black on a crater floor will be brilliantly illuminated before you know it. The wrinkled and convoluted floor of a Mare will appear smooth as glass in a matter of hours. And all of these mutations are visible with the most modest of equipment - no "light bucket" required.

And sometimes transience can be as appealing as permanence. I love knowing the Big Dipper will be there for my grandchildren, and for their grandchildren. But I also find joy in a sunset that will disappear forever in 15 minutes - and find it for that very reason. With the Moon, you can have it both ways. For just this once, you can both have your cake and eat it too. The Moon's features may be eternal, but your view of them is all too fleeting. And to the cognoscenti, there's pleasure in knowing that it's not simply a matter of waiting until next month to see the same pageant of shifting shadows across any given feature. Due to the librations and the eccentricity of the lunar orbit, the same pattern of shadows you see tonight will not recur for another 18 years. (At my age, that basically means that I am always seeing something on the Moon for the Last Time. So you can bet that I pay attention.)

And thus this posting's title - Explorers! I grew up in Arizona, and have fond memories of driving through what was back then in the 1960s an endless wilderness (sadly gone today, all "developed"), seeing at every turn of the road a new horizon, a new distant range of mountains, a canyon or a river valley. That's how I feel today observing the Moon. The advancing line of sunlight is forever opening up new vistas, or at least a new way of looking at old ones. The manner in which that unnamed feature west of Kunowsky Crater revealed itself will not be repeated until 2035! And I was fortunate enough to have seen it... and wonder.

* Title of 1949 short story by Robert A. Heinlein

Explorers!

Last Tuesday evening at an Alpha Ridge impromptu, I decided to make it an exclusively Moon night, and not look at anything else.* Despite my reputation as a Lunatic, I hadn't done that a long time, and it felt good to get Back to Basics as regards lunar observing. I started out, as always, by putting in a relatively low power, 13mm Nagler eyepiece and taking in the Moon as a whole. Then I upped the magnification, moving to a 4.5mm Delos and cruising up and down the length of the terminator, looking for anything particularly eye catching.

Well, what really caught my eye was an intriguing line of three piercingly bright dots off to the right (in my mirror-imaged view) of the day/night line. They were almost starlike in their intensity and pointlike appearance, looking for all the world like a row of streetlights on a dark road. (See above image. The three dots just to the left of center were in  splendid isolation when I first caught sight of them.) I decided to stick with them and see what they would become (a mountain range? the wall of a crater? an escarpment?) as the sunrise overtook them. I first spotted them at about maybe 5:15 or so, and I ended up staying glued to that spot for a good three hours.

Changes occurred much more slowly than I had anticipated. While other features to the north and south of this mysterious line of dots rapidly revealed themselves as crater rims and gigantic peaks, the dots remained stubbornly unaltered as isolated points of light. They didn't merge together or expand in size, but rather multiplied in number. After maybe 20 minutes, there were four of them. then all of a sudden seven, as a tight little triangle of points popped out of the darkness all at once. It eventually became hard to keep track of how many there were, as a host of microdots gradually came on the scene. But for the longest time there wasn't even a hint of their ever joining up to form a recognizable landform.

Finally two set of dots merged into short arcs and the whole collection was assuming the appearance of a bow. I (entirely mistakenly) now assumed I was looking at a highly degraded rim of an ancient lava-flooded crater. And that's where things stood as the evening ended and I packed up to go home.

But that's not where the story ended. Once home, I shot out an e-mail detailing what I saw, and various club members responded with their ideas (a.k.a., guesses) as to the identity of the mysterious feature. It wasn't until Richard Orr sent me his image from Tuesday night (above) that a positive identification was made. I was observing the disconnected summits of an irregular line of hills just west of the crater Kunowsky. I went to Google Moon and turned on the Elevation feature. The feature jumped right out at me. It's also clearly visible in the chart by the incomparable selenographer, Antonin Rukl (right below this paragraph), centered at 36 degrees W, 2 degrees N.

Unfortunately, whatever this landform is, it apparently has no name. At least, none that I can find. Richard noted that the dots were likely "small separate hills making the western boundary of Mare Insularum" but are not parts of a crater rim, nor of a mountain range. At this point, any speculations would be much appreciated!

* I didn't quite devote the entire evening to the Moon, since I began the session with a truly marvelous binocular view of Saturn and Mercury, both visible in a single field of view.

(Probably should have mentioned this earlier, but I was observing using a 90mm Stellarvue refractor on a Universal Astronomics Dwarfstar alt/az mount atop a Manfrotto tripod. No electronics whatsoever. I had to keep the object of interest centered by hand.)