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?

On Moday, August 27th, I set my alarm for 4:40 so that I could wake up in time to view the next morning's lunar eclipse. Alan MacRobert's article in the August S&T hinted that for New Englanders, the Moon might become invisible toward the end of the partial phase, and I was eager to prove him wrong. With the Moon still 2° above the horizon at the beginning of totality, I figured I had a fighting chance. To handicap myself a little, I didn't bring a telescope — just binoculars.

As soon as I arrived at the top of the hill in Danehy Park, I realized that the Moon was bound to disappear before totality. Most of the sky was quite clear, but there was an impenetrable cloud band on the western horizon. But having come that far, I decided to enjoy the partial phase to the fullest.

This was actually a rather novel experience for me. Usually I think of partial phase as a mere prelude to totality, and don't pay it much attention. Fortunately, the partial eclipse was particularly good this time. Even with just ¼ of the disk covered, I could see the dark part of the Moon with my unaided eyes. As the dark bite grew larger, it also became strikingly asymmetric. Its right-hand edge was much brighter than the left. You can just barely see this effect in my photo at right, and it's much more obvious in Dale Ireland's photo of the onset of totality in our Photo Gallery.

My one mistake was not bringing a telescope. I should never neglect to do that when viewing a popular event from a public venue! Sure, observing the Moon through a scope is old hat to me, but it would have been very gratifying for the dozen other people who had gathered there. Fortunately, my 10× image-stabilized binoculars easily showed the crescent phase of Venus, which was rising as the Moon disappeared into the clouds. So at least I had something exotic and unexpected to show to everyone else.

As August winds to a close, I've been reading reports from stargazers at far northern latitudes. They usually start something like this: "Here in southern Alaska, we just had the first half hour of genuine darkness for four months." Or: "In Finland it won't get dark for another two weeks, but that didn't prevent me from observing such-and-such."

The big culprit here isn't civil or nautical twilight, which I've already discussed in another blog entry. It's astronomical twilight, the time when the Sun is 12° to 18° below the horizon. In cities and bright suburbs, or at full Moon, astronomical twilight is a non-issue; the sky is as dark as it ever gets by the end of nautical twilight. But at otherwise dark locations, the sky is still too light for serious deep-sky astronomy.

Most of the year, astronomical twilight doesn't bother me. It lasts about a half hour -- just long enough to get all my charts organized, become dark adapted, and work out some preliminary star-hops. But around midsummer night, at the latitude of Boston (42.5°), astronomical twilight stretches out to a seemingly interminable hour.

Things are dramatically worse at 50°, the latitude of Winnipeg, Canada, or the southernmost tip of England. Here, astronomical twilight swells until it consumes much of the night from May through mid-August. It's sobering to think how much the Herschels accomplished despite the fact that at their location, the sky never gets fully dark for all the time that the Sagittarius Milky Way is reasonably high off the horizon.

I don't think I'm being narrowminded when I speak of astronomical twilight as a bad thing, by the way. Astronomical twilight is a great nuisance for astronomers, but it's far too dark for normal civilian activities. And it's not especially romantic, either. All color has gone from the sky, leaving just a dull glow above the spot where the Sun set.

In Seward (Alaska), Oslo (Norway), or St. Petersburg (Russia), at latitude 60° N, deep-sky astronomy grinds to a complete halt for several months. Here, on midsummer night, the sky doesn't even pretend to get dark. Just an exceedingly long sunset merging imperceptibly into an equally long sunrise.

It's interesting to think what's going on during astronomical twilight. When the sun is 12° below the horizon, that means that the closest spot on Earth that's still bathed in direct sunlight is more than 800 miles away. All the light that you see — and it's still fairly bright in the west — has struggled through those 800 miles of air, and around the curve of Earth's surface. It takes fully 1200 miles of air to fully extinguish the Sun's light and end astronomical twilight!

This also makes it clear that it's hopeless to give a precise formula for how dark the sky is at any given time after sunset. Suppose there's a big band of thunderclouds 500 miles to the west of you. That would probably block 90% of the sunlight, allowing the sky to become fully dark when the Sun was only 15° below the horizon instead of 18°.

How about the true Arctic, the land of the midnight Sun? Most of the people there live not far north of the Arctic Circle. Latitude 70° N just clips the northern tips of Alaska and Norway. I tend to think of this as a land of perpetual cold and dark, but one look at the diagram at right makes it clear just how wrong that is. Even on midwinter night, the time of full darkness is barely longer than it is in Boston! Instead, the three twilight bands have swelled until they occupy a huge chunk of all the hours in the year. In the Arctic, when it's not daylight, it's probably twilight.

What's going on? Well, the Arctic gets just as many hours of sunlight as anywhere else on Earth — in fact, just a tad more. The reason the Arctic is cold is that the Sun never gets very high above the horizon, so its light always hits the ground at an oblique angle. The flip side is that the Sun also never gets very far below the horizon. Most of the time that the Sun's not up in the Arctic, it's skimming just below the horizon, yielding one or another flavor of twilight.

When the S&T website switched over to a new blog style, all the discussions for the existing blogs were lost. It may be sheer vanity, but I was reluctant to let some of those comments go — notably the ones about Fear.

So in my copious spare time, I manually went through all the old comments and re-posted them. To do this, I first had to build an index to all of my blog entries, and having gone to all that trouble, I'm posting it too. Some day, our website should do this indexing automatically, but that will require time and money that we can't spare right now.

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