A couple of months ago, someone in Cloudy Night's Light-Pollution Forum wondered what's the most light-polluted city on Earth. I guessed that it was somewhere in Asia. A different person said that he was sure that North America headed the list. To make a long story short, I was dead wrong and he was absolutely correct.

It occurred to me that if you measure "most light-polluted" by the area where the Milky Way is difficult or impossible to see, then the Light-Pollution Atlas could provide an objective answer. All I had to do was count the number of red and white squares within each metropolitan area, correct for the fact that places at high latitudes are stretched horizontally, and I would be done.

There are a few caveats. As I said in a recent blog, it's unclear how accurately the Light Pollution Atlas captures actual conditions on the ground. Also, many big cities are on seacoasts, and it was tricky to separate the white line representing the coastline from the white for light pollution. Finally, it's quite possible that the methodology behind the Light Pollution Atlas has some kind of regional bias. But it's hard to believe that any such bias could be big enough to explain the differences that I found.

Nine of the top ten light-polluting metropolitan areas are in North America. Sorting by white squares (rather than red and white combined), Tokyo just slides onto the list in the #10 spot. But Tokyo is by far the world's most populous metropolitan area, almost equal to New York and L.A. combined. No city in Europe even makes the top 20.

It's not surprising that cities in the less developed world don't make the list. Beijing, Shanghai, Delhi, Mumbai, and Kolkatta each have light-pollution blobs comparable to a U.S. city of two million, though each of those metropolises have roughly ten times that number of people. But in these parts of the world, energy is far more expensive relative to income, and people don't splash it around heedlessly. Moreover, most of the 120 million or so people living in the map quadrant at lower left are in villages that have essentially no outdoor lighting at all.

But Europe and Japan have standards of living comparable to the U.S. I estimate that the U.S quadrant is home to about 50 million, the European quadrant to about 80 million, and the Japanese quadrant to about 90 million. Yet according to this map, the amount of light pollution in Europe and Japan is far less than in the U.S. Why is this true? Can those areas be a model for better lighting practice in the U.S.? I'll explore those subjects in a future blog. Meanwhile, I would love to hear comments from people with on-the-ground astronomy experience both in the northeastern U.S. and in Japan and/or northwestern Europe.

In 1983 Edward R. Tufte published an immensely influential book entitled The Visual Display of Quantitative Information. The gist of the book is that graphing data is (or should be) a sophisticated art. If you want to convey useful information to your reader, you have to think about the presentation, not just slap data on a page any which way. Tufte's main peeve is with graphs that present data inefficiently or ineffectively, so that you look at them and don't really know what they're saying. A related subject is that the same information can be presented graphically in different ways to make different points.

At right, I've shown a piece of the North America chart from the Light Pollution Atlas re-mapped to a conical projection. On looking at it, most people's first reaction is "My goodness, almost half of the U.S. is brilliantly lit." Whether intentional or not, that's a direct result of the colors chosen to represent different levels of light pollution. (From darkest to lightest, they're black, gray, blue, green, yellow, orange, red, and white.) The most prominent color in this map is green. That's not surprising, since the human eye is most sensitive to that color, and this is the greenest green that you computer monitor can produce, with all the green pixels firing at maximum, and all the other pixels turned off.

To my mind, this is somewhat misleading. Logically, the colors ought to go from darkest to brightest. But the orange zone appears distinctly darker than the green zone, belying the fact that skies are in fact 9× brighter in the orange than in the green. Shown at right is a very minor tweak, using darker versions of green and yellow. This makes the colors more of a continuum, and it's also more faithful to the underlying reality. In fact, the typical reaction of urbanites or suburbanites on first visiting the green zone is that skies are darker there than they ever imagined could be possible.

The differences may be more apparent in a closeup view. At right is an excerpt from the original map showing the northeastern U.S. and southeastern Canada. Detroit is on the left; Philadelphia and New York are near the bottom right of center; and Ottawa, Montreal, and Québec City (left to right) are above them near the top of the map. Prominently dark are the Great North Woods of Maine and the far greater woods of Canada. Less dark but also notable are the Adirondacks southwest of Montreal and the Alleghenies west-northwest of New York City. It looks as though New Yorkers have to go a long, long way to escape light pollution.

Here's the same region using my revised colors. This more or less matches my perception of the Northeast. It's now apparent that there's an almost unbroken corridor of reasonably dark sky — green at the worst — running down the backbone of the Appalachian Mountains. It's a long drive to a gray area from Boston or New York, but there are pockets of green — areas where the Milky Way is very attractive indeed — not too far away.

Here's a more drastic representation of the same data, which would probably seem appropriate to a typical backyard astronomer with little experience of dark skies. I've cranked green and yellow way down so that they look almost dark and boosted red to be a shade of white. Now the main contrast is between areas where the Milky Way is prominent (yellow and darker) and areas where the Milky Way is faint or invisible (red and white), with orange as a transition zone. This would be my guide if looking for a weekday observing site, where long drives are out of the question. Ideally, I would head for yellow or green, but in practice, I would just try to get out of red or white.

Which of these versions matches your perception of the light pollution around you?

Seventeen months ago, I took a break from my weekly blog, entitled Stargazing. Now I've decided to resuscitate it, though I doubt that I'll have time to write a new entry each week.

The entry that you're reading now was inspired by my ongoing obsession with measuring skyglow — a quantity that's immensely important to all stargazers, but very difficult to quantify. (see my online article if you don't know what skyglow is or why it matters.) If you visit someone's backyard, you can see for yourself what his or her light pollution is like. But how can you describe your skyglow to someone 5,000 miles away that you've met over the internet?

The three methods that seem most promising to me are digital cameras, the Sky Quality Meter (SQM) and SQM-L, and the Light Pollution Atlas, which is perhaps best known through its incorporation into the Clear Sky Chart.

Of these, the only method that can be applied without specialized equipment and skills — indeed, without even setting foot outside — is to find one's color zone in the Light Pollution Atlas. Jonathan Tomshine's Dark Sky Finder website has made this extremely easy for anybody in the U.S. or southern Canada.

But the authors of the Light Pollution Atlas have always been happy to admit that its color zones are tentative. They're based on satellite data collected more than a decade ago, over a long timespan, in varying conditions, and massaged by an experimental mathematical model of how skyglow spreadst.

To check the validity of the color zones around my home near Boston, MA, I went to Groton, a town just outside the red zone, and drove from there to my own home deep in the white zone, measuring skyglow along the way with my SQM-L, using a digital camera as a cross-check.

My measurements, shown at right, cast some doubt on the mathematical model behind color zones. For one thing, my measurements were consistently darker than the ones predicted by the key to the Clear Sky Chart's light-pollution maps. More intriguingly, the skyglow did not increase continuously, as I had expected, but followed an unmistakable step pattern. This suggests that highly local conditions play a larger role in skyglow than I would have guessed. The skyglow that I measured remained essentially constant starting 14 miles from the city center, well out in the red zone, until 7 miles from the city center, deep in the white. Throughout this area, it's dark enough to see the summer Milky Way fairly easily when it's overhead. Then, in the next three miles, the skyglow doubled.

Here's my seat-of-the-pants interpretation. I caution that this needs lots more data before it can be taken as a scientific conclusion. I think that the steps on the light-pollution curve reflect local residential patterns, cultural attitudes, and streetlighting practices.

The first big jump happened when I crossed the line from Carlisle into Bedford. Carlisle is a faux-rural suburb with 2-acre zoning, hardly any streetlights, and no bright private lighting. Unshielded mercury-vapor bulbs are for poor people, and garish "architectural lighting" is for the nouveau riche. Old money needs no glare bombs to feel safe nor any ostentatious display to feel self-confident. Houses in Carlisle have dim outdoor lights or none at all.

Bedford is much more typical of a mid-to-outer suburb, with three times Carlisle's population density, significant commercial development, and regular streetlights along the roads. But houses are still pretty far apart, and the street lighting is designed primarily to supplement automobile headlights. There are pedestrians in Bedford, but distances are too far for most people to do errands on foot.

The reading seven miles from Boston was taken at the western foot of Belmont Hill, an escarpment with lots of conservation land and broad estates. Hardly any of the skyglow there has local origins; it's almost all from the urban area on the other side of the Hill.

Then, at the eastern foot of Belmont Hill, the undeveloped land stops abruptly, and from there all the way into the center of Boston, all the houses are cheek by jowl, and the streets have broad sidewalks and closely spaced streetlights. This is where the skyglows starts to climb really sharply — roughly in proportion to the population density.

The color zones of the Light Pollution Atlas suggest a step pattern, but that's actually an illusion — an artifact inevitable in any color-coded map with coarse contour lines. The underlying mathematical model indicates that the transitions should be gradual. But my measurements suggest that abrupt transitions are the rule rather than the exception, at least in the Boston area. More research is needed!

Click here to see a tab-separated table containing details of my measurements.

I've been writing my blog for just one full year now, and it's time to take a break — for an indefinite amount of time. I'm doing a lot more work on the magazine, and it's increasingly hard to find time to write for our website.

Granted, the blog is just a small part of what I write for the Web; the lion's share of my time goes to observing stories like the recent one on the Geminids. But when push comes to shove, it's the observing stories that are indispensable. I'd much rather have 1000 people outside at night using the star charts that I've posted on our website than the same number of people chit-chatting about my opinions during the day. Opinions are cheap, but facts are facts.

Nonetheless, I've had a lot of fun spouting my opinions over the last year, and I still have a couple dozen topics that I've never gotten around to. Maybe you'll see some of them in the magazine! Meanwhile, here's an index to all the subjects that I've blogged:

Dec 19, 2007	The Scientific Value of Visual Observing
Dec 12, 2007	Holmes: Victim of Its Own Success
Dec 7, 2007	A Night in the Life of an S&T Editor
Nov 30, 2007	The Reliability of Visual Observing
Nov 20, 2007	The Amazing Comet Holmes
Nov 15, 2007	Traveling Without a Scope
Oct 11, 2007	Bye for a While
Sep 28, 2007	Big Binocular Messier Survey
Sep 20, 2007	Do the Planet Limbo
Sep 12, 2007	Calendars
Aug 31, 2007	Ridiculously Small Optics
Aug 29, 2007	Moonset Eclipse
Aug 23, 2007	Astronomical Twilight
Aug 16, 2007	Discussions Restored
Aug 14, 2007	Stellafane
Aug 9, 2007	Some Suburban Messiers
Aug 2, 2007	Twilight
Jul 30, 2007	Microsaccades
Jul 26, 2007	The North America Nebula
Jul 24, 2007	Comet Envy
Jul 20, 2007	Anticipating August
Jul 17, 2007	Pollution and Stargazing
Jul 13, 2007	Galaxies and Clusters and Comet, Oh My!
Jul 5, 2007	Strange Encounters Part II
Jun 26, 2007	Strangers in the Night
Jun 21, 2007	The Day the Sun Stands Still
Jun 14, 2007	Decisions, Decisions
Jun 8, 2007	Desk-Chair Science
Jun 1, 2007	Fear
May 25, 2007	Unexpected Connections
May 15, 2007	Big Sky
May 10, 2007	Coda: Binoculars Versus Starblast
May 1, 2007	Binoculars Part III: One Eye Versus Two
Apr 27, 2007	Three Binoculars: Part II
Apr 23, 2007	A Tale of Three Binoculars: Part I
Apr 13, 2007	Stars and Birds
Apr 4, 2007	How Brightly Shines the Moon?
Mar 31, 2007	Better Late Than Never
Mar 22, 2007	Measuring Skyglow
Mar 28, 2007	School Time
Mar 21, 2007	Dressing Up for an Evening Out
Mar 16, 2007	Equipment
Mar 14, 2007	Waiting for Sagittarius
Mar 7, 2007	The Meaning of Stargazing
Mar 5, 2007	A Spontaneous Star Party
Feb 26, 2007	Celestial Time and Human Time
Feb 22, 2007	Instant Astronomy
Feb 19, 2007	June in February
Feb 16, 2007	Stars and Snowflakes
Feb 13, 2007	Mercury Retrospective
Feb 9, 2007	Keeping Myself Honest
Jan 31, 2007	Hello World

John Henry said to his captain:
A man ain't nothing but a man.
But before I let that steam drill beat me down,
I'll die with my hammer in my hand.

For more than 100 years, it's been obvious that astrophotography has far more scientific value than visual observing. Visual observing reigned supreme in a few niches until recently. For instance, normal cameras can't match the eye at capturing fine details on the planets during brief moments of steady seeing. But with the advent of video cameras and computerized image stacking, even that advantage was lost. It's probably fair to say that there's no astronomy that the human eye can do that can't be done as well or better by electronic imaging. Moreover, electronic devices can make images across the entire electromagnetic spectrum, almost all of which is invisible to the eye.

Most important of all, imaging leaves an objective, auditable trail. Visual observations, by contrast, are notoriously unreliable. The history of astronomy is littered with sightings that proved to be false — dating back to the invention of the telescope and before. Most people have heard of the canals that Percival Lowell fantasized seeing on Mars. But did you know that Galileo saw cities on the Moon? That particular error has been swept under the rug by people eager to present science as an inexorable, inevitable, one-way march to the truth.

Yet amateur astronomers continue to make valuable contributions to astronomy using nothing but their eyes and wits. How is this possible? And how much longer can it go on?

The discoveries that loom largest in the popular imagination are comets. That's no doubt partly due to the fact that the brightest ones are spectacular to look at, and many fainter ones make spectacular photos. But perhaps even more important is that fact that comets are named after their discoverers. We're a society that idolizes the individual — despite the fact that never before in history have individual contributions counted for so little.

But only a small fraction of comets are discovered by amateurs these days, and of those, more are found by imaging than visual observing. I bet that most of the amateur-discovered comets would be found by the pros not long after, and that the time lag wouldn't matter much.

Supernova discoveries don't get nearly as much press, but they probably have more scientific value. Again, these would eventually be found by the pros. But supernovas change a lot faster than comets (usually!), and the early stages of a supernova's outburst are very interesting and important. Even if the amateurs only speed discovery by a few hours, that can have considerable value.

Supernovas are extreme examples of variable stars, and amateurs have played a central role in variable-star observing for a long time. But these days, the lion's share of the good work is done with CCD cameras. A skilled amateur can measure a star's brightness with an error of 0.1% using a CCD camera, compared to 5% or 10% for the best visual estimates.

But Arne Henden, head of the American Association of Variable Star Observers, assures me that visual observers still play a key role in monitoring cataclysmic variables — stars that erupt unpredictably, including supernovas, novas, and other less glamorous categories. That's because people skilled at observing these stars are scattered all around Earth, eager to be mobilized with a moment's notice. That makes it possible to monitor the stars continuously; it's always nighttime somewhere on Earth.

To my mind, the area where visual observing is most important is meteor science. It just so happens that humans can monitor a huge field of view in very dim light and spot anything that moves. This ability, which presumably evolved for avoiding predators, happens to be ideally suited to detecting meteors as well.

And as with variable-star observers, there's a worldwide network of people who like nothing better than lying outside in the freezing cold, at a time when all self-respecting people are asleep, keeping careful track of minuscule blips of moving light. So most of what we know about meteors comes from visual observation.

I have to conclude that visual observers are most valuable when they're acting in concert, not as heroic individuals. And just as John Henry achieved glory by doing a purely mechanical job, visual observers are at their best when they're emulating machines: objective and dispassionate. Really, their main advantage is cost. If you had to pay meteor observers by the hour, it would cost a fortune; machines would do the same job cheaper. But amateurs do it for love, not money.

Well, I've posted the article about 8P/Tuttle, so now I can discuss comets with a clean conscience.

Incidentally — while I'm on the subject — I decided to post the S&T charts in black-on-white format, as PDFs. The way I figure it, color charts are easier to read on the screen, and more attractive in the magazine. But when we post really detailed charts like these, most people are going to print them, so that they can carry them into the field. And on most home printers, charts with dark backgrounds are ugly, smeary, tend to jam the printer, and use lots of expensive ink. So I'm inclined to use traditional bright-on-dark for simple, at-a-glance charts, but black-on-white for detailed charts. What do you think?

But that's not what I set out to write about. Last weekend, I observed Comet Tuttle for the first time under reasonably dark skies. And naturally, I took a look at Comet Holmes too. What's odd is that I was more excited about faint, featureless Tuttle than dazzling Holmes. I'm beginning to take Holmes for granted.

Yes, Holmes is overwhelmingly big and bright, and shows amazing detail too. But it changes so little from one night to the next, either in position or appearance. It's almost as though the sky has acquired a new deep-sky object, a permanent fixture. As far as I can tell, it has dimmed not at all in the last 30 days. At this rate, it's going to remain a naked-eye spectacle for the better part of next year!

There are benefits to not having a backyard to observe in. When I go out with my telescope, I can look for a really good spot instead of having to settle for all the obstructions that plague most backyard stargazers. But it also means that every observing session requires advance planning — I can't just step outside on a whim. And that, in turn, means that I'm totally at the mercy of the weather forecast. An unforecast clear night might as well not happen.

Last night was the reverse: it was forecast to be clear, so I invested the 1.5 hours required to drive round-trip to my astronomy club's observing field. In fact, the clouds started to move in not long after I arrived. But that still left me enough time to accomplish my primary observing goal.

With all the (well-deserved) hoopla about Comet Holmes, it's easy to forget that another major comet is creeping up on us. The January issue of the magazine has a fine story about Comet 8P/Tuttle, but we've barely said a word about it on the Web. And it looks as though I've volunteered myself to post that story.

It's tricky to say when such a Web story should go live. On the one hand, our star charts are better than anything else on the Web, and it's a shame not to make them available. On the other hand, the Web is aimed at a broader audience than the magazine, and we don't want to encourage people to go out and look at a comet that will disappoint them. Only one way to make that judgment — have to look for myself.

I was pleased that I found the comet fairly easily using the chart in the magazine (excerpted at right). And that despite the rather poor suburban conditions: magnitude 19.2 per square arcsecond as measured by my Sky Quality Meter. But a showpiece it's not — not yet, anway. I could see it with direct vision at 40× in my 7-inch scope, but barely. With Comet Holmes as an alternative, only a hard-core comet-hunter is going to seek out 8P/Tuttle. Most hardcore comet-hunters subscribe to S&T, and the ones that don't know how to make their own charts.

So it looks as though I don't have to hustle yet. Comet Tuttle is brightening rapidly, but it'll still be a couple of weeks before it's of much interest to the broader public.

People sometimes ask me whether visual astronomy — looking through a telescope's eyepiece, as opposed to photography or electronic imaging — still has any scientific value. The answer, somewhat surprisingly, is yes. Astronomy still has a few niches where visual observers make significant contributions. I'll give examples in future blog entries.

But visual astronomy has many drawbacks. One problem that's plagued it since Galileo's day is reliability. How can you be sure that another observer's report is honest and accurate? Indeed, how sure can you be of what you see yourself? It's a critical issue for anybody straining to see things on the edge of visibility. If you don't try at all, you're greatly handicapped. Try too hard, and you start to see things that aren't really there.

The most egregious cases are people who lie about what they see. Little better (maybe even worse) are people like Percival Lowell, who popularized the canals of Mars. His sin was lack of objectivity. The canals on Mars were controversial, and Lowell was hell-bent on proving their existence. With an attitude like that, he could hardly help seeing them, despite the fact that they don't really exist.

But even completely honest, objective observers can be fooled by optical illusions. Everyone sees the Moon as being bigger when it's near the horizon than when it's high in the sky. Knowing that this is false makes no difference; the illusion is wired into the human brain.

An interesting controversy erupted recently on the Deep Sky Forum on Cloudy Nights — though the arguments have degenerated somewhat recently. Here's the situation.

Many if not most people see green tints in the brighter parts of M42, the Orion Nebula. There's no controversy about that. There is indeed green light, emitted by excited oxygen and hydrogen atoms, and it's bright enough to stimulate color vision. The observation is accurate.

Some people (including me) have also seen pink or reddish tints when observing this nebula through big telescopes. Enough people have reported this that we can be sure it's not just imagination. And there's also no doubt that a lot of the nebula's light is indeed red. But here's the kicker. Human eyes are notoriously insensitive to red light at low intensity. Laboratory experiments indicate that the red light in M42 isn't bright enough to stimulate color vision. People do indeed sometimes see red at low light levels, but its an illusion that can be created by any color light, not just red.

So it's possible that the red tints of M42 are both accurate and illusory! In other words, the nebula is red, and people see it as red, but there's no causal relationship between those two facts. Of course, it's also possible that the laboratory experiments are wrong, or don't faithfully replicate the real-world situation.

What a mess! It's really hard to think of experiments that can say for sure what's going on. But astronomy is full of such unexplained sightings.

For instance, there are the notorious "transient lunar phenomena," the ashen light on the unlit side of Venus, and reports by binocular observers that the visual disk of the Andromeda Galaxy stretches across 5° of sky. All of these defy scientific explanation, but have been reported by several reliable observers.

I'm a little bemused by all the reports that Comet Holmes is getting harder to see. No doubt that's true, but I can't tell by firsthand experience, because each time I've viewed the comet, the conditions have been radically different from the previous time. (Remember, I was traveling in India when the comet first flared up.) But I've found it easily every time I've looked, and it's always appeared both bigger and brighter than I expected.

Most of my sightings have been through my 10×30 image-stabilized binoculars, which seem to be nearly ideal for this particular job. All along, I've found Comet Holmes a little hard to snag without optical aid because it's in such a crowded star field. And because of the comet's immense size and modest surface brightness, I find it much more prominent through binoculars than through a telescope.

My most recent sighting was on Sunday night, around 3h UT on Nov. 19, from my apartment in Cambridge, MA. The comet was immediately visible through my 10×30 binoculars, a bit bigger than 30', with Alpha Persei (Mirfak) right on its edge. A brighter elliptical blob about 10'×20' extended from the center of the coma to the edge.

This was despite the urban skyglow (brighter than mag 18.0 per square arcsecond) and the first-quarter Moon. I'd rate the overall visibility roughly equal to the Andromeda Galaxy, and much higher than any other galaxy. Vastly brighter than M33, for example!

My urban skies are only about 50% brighter at full Moon than without a Moon, so I'm predicting that I'll be able to see the comet with my binoculars right through the full Moon period. And after that, it should start to get more prominent again — at least when viewed from dark sites. I can't wait to see how big the coma has grown by the end of the year!

Well, here I am, back from India. As I said, I didn't bring a telescope with me. On the whole, I don't regret that decision. My lightest "serious" telescope rig adds up to roughly 10 pounds — a pretty major encumbrance. And the equipment's cost is as much of a problem as its weight and bulk.

Consider, for instance, traveling on a typical Indian bus. Most luggage goes on top, where it's liable to be stolen or crushed — not a very attractive option for a telescope. But carrying it on your lap in a crowded bus isn't especially attractive either.

Instead, I brought a truly minimal set of astronomical equipment: my 10×30 image-stabilized binoculars, a red flashlight, and Orion's Deep Map 600. In fact, Deep Map 600 was the only real "extra." I would have brought binoculars anyway, to look at birds, distant mountains, and so on. And flashlights are essential in India, where the electric power is notoriously unreliable.

The binoculars came very much in handy when Comet Holmes underwent its unexpected and startling outburst. And I was also very glad to have them during our 3-day "camel safari" in Rajasthan. A camel safari is a slightly hokey touristic experience, but it does give some sense what it was like to travel in one of the great camel caravans that used to cross this region for centuries or millenia. Everyone agrees that the highlight is sleeping on the dunes under a genuinely dark sky.

We were at latitude 26° north — about the same as Miami, Florida or Brownsville, Texas. That allowed me to see a big chunk of sky between declination 30° and 50° south that's not accessible from my home in Massachusetts. The binoculars were of limited use in the evening, when the galaxy fields of Sculptor and Fornax were transiting the meridian. But they were great in the early morning for viewing the splendid open clusters of Puppis and Vela. I was particularly struck by the contrasting pair NGC 2477 and NGC 2451, the former a patch of creamy light through binoculars, and the latter coarse and well resolved. Very much like M46 and M47.

But I found myself missing a telescope not for my sake but for my companions. We had a guy from Australia and one from England in our group, and the Englishman had never so much as seen the Milky Way before, much less looked through a telescope. I would have loved to show him a few things.

I missed a telescope even more a couple of weeks earlier in the trip, when we were in the Himalayas. We ended up spending a night unexpectedly in a small village, and we hung around outside in the evening as the glow disappeared from the high peaks and the stars started to come out. Not surprisingly, every child in the village was out there with us. But none of them spoke any English, and our Hindi is extremely rudimentary, so we didn't have much to say to each other. I really, really wished that I had my telescope with me so that I could have spoken to them in the universal language of astronomy!

I normally try to post at least one item per week in my blog, but I missed last week. That's because I've been frantically busy preparing for a four-week vacation.

I'm off to India. Astronomy's not one of my primary goals, but every place on Earth and every human endeavor has some relation to astronomy, the oldest and most universal of all the sciences (except maybe medicine). So whenever and wherever I go, my vocation and avocation travel with me.

Moving 15° farther south potentially opens up new celestial vistas. But the great southern objects in autumn's evening sky are all galaxies, which require a big telescope to do them justice — and I'm not about to schlep a scope along on this trip. Maybe I'll find out how many of the Fornax galaxies are visible through 10×30 binoculars.

My primary observational goals are to show my wife two things she's never seen: Canopus, the sky's second-brightest star, and the zodiacal light. Eta Carinae will also be poking above the horizon just before dawn, but it will be so low that I doubt we'll get a decent view.

Astronomy is also tremendously important in India's cultural heritage. If you think people are crazy about astrology in the West, you should see India! But that's a topic for a whole 'nother article ...

On a more sober note, it was India that gave us the mathematical tools (via the Arabs) that were required to make the jump to modern science. And India is home to what are perhaps the most architecturally striking astronomical observatories in the world: the five Jantar Mantars constructed by Maharajah Jai Singh II (1688-1743).

What intrigues me most about these observatories is how archaic they were when they were built. Though Jai Singh was a Hindu, his observatories are clearly descended from Islamic astronomical tradition. They very much resemble the observatory in Samarkand built by Ulugh Beg, another (far greater) astronomer-king. But whereas Ulugh Beg's observatory was cutting-edge when it was built in the 15th century, telescopes rendered naked-eye observatories obsolete a century before Jai Singh built his. And Jai Singh, a highly cultured man, must surely have known that.

So perhaps the Jantar Mantars were built more for publicity than for practical use. I suppose we'll never know.

It was Jay Freeman who gave me the idea of observing all the Messier objects with each instrument that I own. It's turned out to be a very useful habit. It gives me an excellent sense of the instrument's capabilities, while also reinforcing my memory of where each object is, what it looks like, and how to find it. Ideally, I'd like to be able to find every Messier object with every instrument at every level of light pollution by memory — though that's obviously a utopian goal that can only be approached, never completely realized.

Ever since purchasing my 15×70 binoculars, I've been reminded of Jay's comment that 70-mm binoculars are the easiest instruments for doing a Messier survey. They can be swiveled very quickly, yet they're big enough so that most of the Messier objects pop out instantly as soon as they enter the vast field of view — assuming that I'm under reasonably dark skies.

Last weekend was late first-quarter Moon, so I had to get up before dawn for deep-sky observing. I ended up chasing down all the early-winter Messier objects — the ones between RA 0 and RA 6 — in a few minutes using my 15×70 binoculars. Only when I was writing down my notes a couple of days later did I realize that this had completed my Messier survey with that instrument.

After my quick scan, I went back to view each of the objects more carefully. And here's where one of the drawbacks of binoculars became painfully apparent. One of the reasons that I can find deep-sky objects so quickly with binoculars is that once found, the objects display depressing little detail. So I'm not tempted to linger over each object as I would be if using a telescope. There are a few star clusters (the Pleiades, for instance) that really sparkle at 15×, but they're the rare exceptions.

Still, there were a few pleasant surprises. For instance, I was able to make out the outer loop of the Orion Nebula — the one that's almost 1° in diameter, passing near Iota Orionis. That's not an easy target even in telescopes with significantly more aperture. It's a reminder that using two eyes is especially valuable for viewing subtle nebulosity.

I do finally understand why 15×70 binoculars are popular with some beginners, though. For simply tracking down deep-sky objects — as opposed to seeing detail in them — the combination of the binoculars' enormous field of view, straight-through pointing, and pretty-huge light grasp is hard to beat. That could avoid a lot of the frustration that many beginners experience.

One of the major new features making a debut in the October S&T is a table showing the visibility of the planets. It's in "Sky at a Glance," the first page of the gatefold.

The current design is reasonably clear and effective, but I think I've figured out a much better way to present the information. With any luck, it will run in January.

One problem that's given me a lot of grief is: exactly when does a planet qualify as "visible?" To be more precise, when a planet is near the Sun, how high does it have to be at sunset to ensure that the planet will be visible sometime before it itself sets?

This is an excellent time to study the subject, as we happen to be in the middle of a very poor evening apparition of Mercury (as seen from the Northern Hemisphere). So I went out last night to see if I could find the elusive planet. Frankly, I was pretty confidently expecting failure — even with binoculars. Mercury is now 7.4° above the horizon at sunset, which is mighty low. And it's mag -0.1, which certainly isn't faint, but is nowhere near as bright as it sometimes gets.

But what do you know? At 7:20 pm EDT, 32 minutes after sunset, with the Sun 6.8° below the horizon, I caught a surprisingly bright light shining through the orange glow just 2° above the horizon in my 10×30 binoculars. That was Mercury, looking much like a distant car headlight shining through fog during the day. And as I stared at the spot naked-eye, it flickered into momentary visibility ever few seconds. (Alan MacRobert tells me that this was nothing more than everyday "twinkling," which takes place extremely slowly when you're looking through 10 or 20 atmosphere's worth of air.)

This also gives some kind of answer about the Venus-Spica encounter that we've touted in the online Sky at a Glance. I had some doubts whether this was really a binocular challenge or a fool's errand. Now I know that there's at least some hope — though I'll point out that I did not see Spica last night. Then again, conditions were far from perfect, and I was using pretty small binoculars. Still, if (against the current forecast) it turns out to be clear on Friday, I'll be looking with a telescope, not binoculars.

I'm very curious what success other people have at viewing this elusive but potentially exciting conjunction. Please report back here. And what's the lowest that you've ever seen Mercury and Venus through the glow of the setting (or rising) Sun? How low can you go?

A while I ago, I mentioned the fact that the Hindu festival of Divali always takes place at new Moon. That's particularly appropriate in this case, because Divali is celebrated by lighting candles so that the hero Ram can find his way home after a 14-year exile in the wilderness. And why would Ram need candles if the Moon were up?

This put me in mind of the fact that all Hindu, Jewish, and Islamic holidays are necessarily synchronized with the Moon, because all three religions use calendars where months are strictly tied to the phases of the Moon. This year in particular, that's driven home by the fact that both Rosh Hashanah (the Jewish New Year) and the holy Moslem month of Ramadan, start at sundown tonight, on the day after a new Moon.

Speaking as a stargazer, our own calendar is quite annoying. The synodic month (from new Moon to new Moon) is 29.53 days, but our months average 30.44 days. So the Moon phases fall behind about 11 days each year. What a pain! Wouldn't it be handy if you knew that the Moon would always be new on the 1st, instead of having to look it up all the time?

In modern society, hardly anybody except for astronomers pays attention to the Moon, except maybe for aesthetic reasons. But before electric lights, you couldn't ignore it. At full Moon, you could move freely all night long. At new Moon, you had to grope your way. It's pretty remarkable that Julius Caesar decided to "regularize" the calendar by cutting months adrift from the Moon.

Before Caesar, Romans used the same sensible calendar as the Jews (and Hindus): the lunisolar calendar. Months stayed in sync with Moon phases, years stayed in sync with seasons, and a 13th month was added every 3 years or so to keep the months from slipping with respect to the year. Presumably, the Romans decided that the administrative hassles of having a variable number of months per year outweighed the benefits of having meaningful months. Romans were big on regularity.

The Moslems took the far more radical step of cutting the year loose from the Sun. Their years average 354.36 days — exactly 12 synodic months. That means that each Ramadan arrives 11 days earlier with respect to the seasons.

That's going to be very unpleasant for lots of people in another few years, when Ramadan arrives in the heart of summer. Why? Because Moslems are required to fast from sunrise to sunset all month long. That's one thing in December, and quite another in July.

I've always wondered whether Muhammad would have received this particular command from Allah if he had lived at a higher latitude. (I'll point out without editorializing that when God speaks to a prophet, the message is always couched in the receiving culture's terms.) Mecca and Medina straddle the Tropic of Cancer. From that perspective, having the rigor of fasting vary cyclically by a few hours over a span of many years is probably a worthy spiritual exercise. It must seem very different indeed in Tatarstan, one of the main Moslem areas of Russia, at latitude 54° N. Midsummer day there is 17 hours long!

All in all, I still like the old-fashioned lunisolar calendar best. But as far as I know, no country today uses a lunisolar calendar for civil purposes. And when all is said and done, why should they? Electric lights have made the Moon obsolete.

I've also wondered about the obsession with the Sun in modern Western culture. Voluntarily baking in the Sun was unthinkable in Western cultures prior to the early 20th century, and it's still unthinkable in most of the world. The standard explanation is that when most people worked outdoors, being pale was a sign of prestige — being a member of the leisure class. And now that most people work indoors, being tan is a sign of prestige.

But I think it goes deeper than that. Maybe it's a funny kind of compensation for the fact that every aspect of nature besides the Sun has been banished from everyday life. What do you think?

What's the smallest instrument you've ever used to view the night sky? My smallest is a 6×15 monocular about the size of a cigarette pack. How are the views? Well, frankly, though I'm no big-aperture snob, 15 mm is not very satisfactory for astronomy.

So why do I use it? Well, it's so small that I can carry it essentially everywhere I go — even walking to the corner store. That's mostly handy when an unusual bird turns up. But every now and then I also get an unexpected urge to view something in the night sky.

The tiny monocular's not much, but it's better than my unaided eyes. It does a fine job on the Moon, and it'll usually show two or three of Jupiter's moons as long as I rest it against a solid support. And the views of M44, M45, and the Hyades aren't half bad.

My 8x32 monocular is in an entirely different class. The 6x15 gets used by accident; this one I bring intentionally. When I'm observing in the city, everything has to go down and up 2½ very tall flights of stairs. And when I'm carrying two telescopes, or my Dob plus an SLR on a tripod, there's a real premium on weight and bulk. That's when I bring the monocular instead of my 10x30 binoculars.

I rarely purpose-view deep-space objects (DSOs) with the 8x32 monocular, but it's very handy for picking Mercury out of the twilight, locating mag-6 stars in the city, and working out star-hops in advance.

Last Friday the Moon rose a half hour after the end of astronomical twilight — not long enough to settle in for serious telescopic observing. So I decided to spend the time seeking out DSOs with the 8x32 monocular. I ended up viewing 20 Messier objects plus my favorite small-instrument open-cluster triplet: IC 4665, NGC 6633, and IC 4756.

Rather than use charts to locate my targets, I used my 15×70 binoculars as a "finder" for the little monocular. Bright DSOs popped out immediately through the bigger instrument, enabling me to work out a star-hop to be used with the monocular. The method was fast and effective, but after the rich, luscious view through big binos, the little 8x32 inevitably seemed feeble by comparison.

The discrepancy was most striking on M8, the Lagoon Nebula. Sure, the monocular showed the nebulosity easily, but the view was lackluster, a far cry from the 15×70 binoculars' jaw-dropping image. With a couple of exceptions, the globular star clusters were also a disappointment, showing either as bright but nearly stellar or faint and nearly stellar.

Things were better with the open star clusters and wide-field vistas. Many of the brighter clusters resolved into individual stars, and IC 4756, though unresolved, was a lovely ethereal glow. The star cloud M24 was impressive, and M18, M17, and M16 lined up neatly above, all fitting easily into a single field of view.

For something that slips easily into any coat pocket, the 8x32 monocular does a surprisingly good job. So what's the smallest instrument you've enjoyed using to view the night sky?