Short note: Venus and Jupiter

For the next several days, Venus and Jupiter will be quite close together, looking like two bright stars in the western sky an hour or so after sunset. Take a look.

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Disagreement is not hate

Here I summarize a Facebook conversation that was very well received.

Just one word for everybody in these controversial times: Disagreement is not hate.

The reason I believe in disagreement without hate is that I believe in objective truth. I am trying to get things right, not merely get power. Truth is out there, and our grasp of it is imperfect, and we can improve our grasp on it by debating it. If I did not believe in objective truth, all debates would be nothing but power struggles and I would want to do nothing but crush the enemy.

Some contend that there are no real facts, that nothing is true or false apart from what we imagine or "construct" in our own minds or receive from our culture. But there is a logical problem with this. If a theory claims there is no truth, how can that theory claim to be true? And if it can't, then how can it say anything at all?

Of course we all see reality from our point of view. But facts are able to overcome our point of view. Many of us experience this every day. That is why we call them facts.

Last point. Commitment to objective facts is a point on which all science agrees with classical Christianity, as against some new intellectual fashions. Unless you believe there are objective facts, you can't even start to disagree rationally about what the objective facts are.

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Whoa, let's not wipe the South off the map!

I stand by my recommendation not to fly the so-called Confederate flag in this day and age. But I am alarmed by the anti-Southern backlash that seems to be occurring among businesses trying to "ban" the Confederate flag.

Of course, it makes sense to refuse to sell cheap mass-produced flags, buttons, and T-shirts that are likely to be used as racist symbols or propaganda. But wait a minute...

I'm not on board with the idea of banning computer games that involve the Civil War. That was some interesting and military important history! And it seems silly to let people pretend to fight alongside Attila the Hun but not Robert E. Lee. Now, if the games have explicitly racist content, that's a different story. But that would have drawn criticism before now.

Nor should there be any ban on the resale of historical artifacts, books, or other items aimed at the study and appreciation of history. I've seen people wondering if genuine U.S. commemorative coins such as this one could still legally be sold on eBay.

And what about toys and souvenirs from the past? Such as toys from the TV show "The Dukes of Hazzard"? They used symbols that we now consider in bad taste, but I don't recall seeing any explicit racism on their show. It was made in an era when racism was already unacceptable. All that has happened since then is that we've become more sensitive about some symbols.

I've even heard from a fellow author whose publisher told him, "in the light of recent events," not to wear a cowboy hat in his picture on the book cover. I replied that he needs to find an American publisher — one that knows about all 50 states!

Regional bigotry is just as ugly and destructive as any other kind of bigotry, but there are slices of the United States, particularly in the Northeast and California, where people are genuinely contemptuous of their fellow citizens elsewhere. Expressions of prejudice range from smug New Yorkers talking about how the rest of the country is nothing but "cow pastures," to young job-seekers who won't go where the jobs are because they've convinced themselves that only a few fashionable cities are fit to live in.

There is also regional discrimination disguised as high-minded political activism. The tactic is to choose a recent political change — today it might be gay marriage or something environmental; there's a different issue every few years — and blacklist the states in which that change has not yet gone through. If you change issues often enough, you can keep many of the southern and central states on a perpetual blacklist, simply because they move slower and you can always find something they haven't done yet. You can even attribute evil motives to them.

And best of all, you can avoid having meetings in more than just a few states, while still claiming to be a national organization. I have seen this done.

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An extremely important fact about communication

This week, a lot of people have realized that by flying the (so-called) Confederate flag with no evil intent, and maybe even with little seriousness, they were inadvertently giving encouragement to some very bad elements in our society. So they stopped.

A few, however, have asked (in the words of one of my friends), "Why should I have to self-censor?"

The answer is one of the most important facts about communication, and it can be expressed several ways. One way to say it is that communication takes place in the mind of the hearer, not the speaker. You cannot convey your intention to another person unless you do it in that person's language. You cannot simply convey your thoughts into another person's brain, à la Vulcan Mind Meld.

Another way to express this is that when you use language or symbols, you're using the community's resources, not your own. If you decide for yourself that "dog" means what the rest of us call a cat, people will not understand you. You have to use language the way other people do, or not at all.

This means that, yes, you do have to "self-censor" — not your message but the way you express it. You have to use words and symbols with awareness of how other people will take them, including people outside your immediate audience. And that audience may not be what you want and may not think the way you want it to think. You have to craft the message so that it will be understood.

In the case of the Confederate flag, the situation is complicated by other factors. Many of us were taught a whitewashed version of southern history in school and grew up believing that the flag stood only for the noble ideals of self-government and local pride. But the historical record tells us that, from the beginning, the Confederacy (and hence its flag) stood for racial oppression. The mid-20th-century attempt to "retcon" the Confederate flag into something else was never completely successful, and now people are realizing it failed.

See also what I wrote the other day.

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Cleaning up the back yard

Thirty years ago, our back yard was surrounded by an embankment planted with cedar and juniper bushes. Over the years, the cedars and junipers reached the end of their natural lifetime, and other plants took over — unwelcome plants. We had it weeded out a couple of times (requiring heavy-duty tools wielded by professionals), but it remained messy.

A few weeks ago, we discovered ticks in it. We think we got rid of them promptly with insecticide, but we felt something more needed to be done.

So today our friends from Porterfield Stump and Tree (a relative of the Porterfield who built the house) came and cleared the embankment and trimmed trees and shrubbery. Here are "before" and "after" pictures:

In place of la selva oscura we have a bright, open area. The embankment is covered with mulch that will soon darken. A large amount of fresh ground has been exposed (where the cedar and juniper had spread out of bounds) and is about to be seeded with grass (right now you see wheat straw). Next year, we'll get something planted on the embankment.

And we identified the animal that the dogs had been tracking in the juniper. It was a three-foot copperhead snake! I'm glad they didn't find it!

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A bit of forensic typography

Today I was able to help a lawyer with an unusual forensic issue. Not giving away any details, let me just say that it had to do with a typewritten (or word-processed) copy of a document whose copyright ownership changed in 2000. The copy was legal if made before a certain date that year, but illegal if made later.

The lawyer first thought it might involve early Selectric typewriters or composers, which is why I was called on. Actually, though, it was daisywheel- or laser-printed.

Based on detailed study of typeface and print quality, I was able to report that:

• The document used a style of word processing that was popular during the DOS era (roughly 1985-1995) and markedly less popular later (though it can still be done today).
• There was certainly nothing present that indicated a later date.

Never a dull day!

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Did I see action on the sun?

An active sunspot region is turned toward us, and yesterday (June 22), there was a solar flare that caused displays of the aurora borealis as far south as the northern tip of Georgia. Misleadingly, NOAA's real-time map led me to believe the aurora had ended before it got dark in North America, and I didn't look for it.

This afternoon (June 23) I photographed the sun using my Celestron 5, Thousand Oaks solar filter, and Canon 60Da. The weather was unseasonably hot (97 F). Yet I got relatively steady images because I had stored the telescope outdoors, in the shade, so that it would be near ambient temperature, and when I put it on its pier, I avoided having the sun shine on the sides of the tube as much as possible.

The picture you see above is a stack of four, de-Bayered and partly histogram-adjusted in PixInsight, downsampled × 2, rotated, and saved as TIF, then stacked with AutoStakkert (in planet mode; surface mode doesn't work well with the sun because the surface is too blank), then sharpened with RegiStax 6 and given final contrast adjustment with PixInsight again.

Look closely at that sunspot group. Here it is, skipping the final reduction of the image size for the Web:

There's a bright spot in the penumbra of a sunspot.

Did I record a white-light solar flare, like the one Carrington saw in 1859?

Probably not, although I'm not an experienced sunspot observer and would welcome input from others. The spot brightened up a good bit due to digital enhancement. Here is a single exposure, contrast-adjusted but not digitally sharpened:

What we see is a spot of basically normal photospheric brightness, right there in the penumbra of a sunspot, which should be darker. For the record, the pictures were taken from about 1430 to 1435 EDT (1830 to 1835 UT) on June 23. Spaceweather's daily sun image, taken some hours earlier, shows a light patch in the same location.

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The Plan 9 Newbie's Guide

Now that Coraid appears to be out of business, I want to preserve for posterity something I wrote while working for them in 2008. Click here to read the Plan 9 Newbie's Guide.

Plan 9 is a strange little operating system, similar to UNIX, named after a bad science fiction movie and notable because of its simplicity and the fact that it is the smallest PC operating system with a GUI and serious software. It is much simpler than Linux and one can be more confident in its reliability. So it is popular in embedded systems, including the processors in Coraid's disk hardware. That's how I got involved with it.

Plan 9 has a cult following and will probably remain available (and free) for decades.

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A note to South Carolina

Yes, we honor Robert E. Lee for his military skill and his nobility in the face of defeat. And we honor Wernher von Braun for his scientific accomplishments and his good citizenship. But we do not fly the flag that either of them fought under when they were in the army.

One more data point. If you think the Confederacy was mainly about self-government, please read what its vice president said at its outset. That is something they did not tell us about in Georgia public schools in the 1960s. In fact, around 1967 there was a contest for an essay about Alexander Hamilton Stephens. I did not enter. I wonder if anyone dared to say in their essay, "He was dead wrong about the most important human-rights issue in American history."

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Radio Shack

"GranDad, what was a Radio Shack?" That a question I expect to hear in the future...

The Athens Radio Shack continues to die a very slow death, and I made another final visit to it today. At 10 cents on the dollar, I cleaned them out of gold-plated phono plugs and a number of other useful connectors.

It has been too long since I've done any non-trivial electronics. My last project, almost three years ago, was a dimmable automotive light that was just a slight variation on a circuit I had designed earlier. Maybe later this summer I can finally get back to the breadboard.

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How to open minds

A nugget from this morning's sermon by Dr. David Mills, who got it from another source that I didn't catch.

These are the four questions that he asks people who tell him Christianity is bunk. They are actually good questions for opening minds on any subject.

(1) What do you mean by that?

(2) What is your source of information?

(3) How do you know that what your sources say is true?

(4) If by some chance you were wrong, would you want to know?

Dr. Mills cautions that we should be gentle. Some people crumble and become hostile after the very first question. That's how you know they are passing around a slogan or "meme" without attaching an exact meaning to it.

And if the source is "a meme I saw on the Internet" and the authority is "my brother-in-law's cousin said to pass it along," then you know you are doing battle of wits with an unarmed opponent!

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Binoculars are better than ever

I've looked at a lot of new binoculars recently, to see what was new, and have concluded there's not much out there that will serve me better than what I'm already using. Nonetheless, I've learned some things that are worth passing on.

(1) They cost less than ever before. In the 1950s a pair of marine 7×50's cost $300. Inflation-adjusted, that is $2400 in today's dollars, and to spend that much money today, you have to buy Zeiss's or Steiner's very best. You can get usable 12×60 astronomy binoculars from Celestron for under $80. Yes, for the price of two tanks of gasoline!

Note: At the low end of the price range, expect a lack of ruggedness, which may not be a serious drawback for astronomers, but the binoculars may get out of alignment after substantial use. Also expect more unit-to-unit variation in optical quality. Nowadays, with computers, anyone can design good optics; the question is who can manufacture them consistently (or afford to throw out the rejects).

More to the point, $200 to $300 gets you seriously rugged binoculars with high optical quality. Astronomers need ruggedness less than sportsmen do, so if you're an astronomer, be sure not to pay too much for that. But as the price goes up, so does the optical quality.

(2) There's more focusing range. Twenty years ago, relatively few binoculars would focus on infinity with my nearsighted eyes (-5.00D) with my glasses off. Today, they almost all do.

(3) 7×50 is no longer king of the hill. This is a rather complicated point, so bear with me.

In my youth, most binoculars were 7×35 or, if you could afford it, 7×50. The latter were recommended for astronomy and for use at night because the large exit pupil gave a brighter image.

The true optical situation is not quite what we thought. Although a young person's pupils will open to 7 mm and take in the entire output of 7×50 binoculars, most adults' pupils don't open quite that wide. And the brighter image did not necessarily improve visibility of dim objects, especially in astronomy — as much as anything, it just added glare. Even in a young person's eyes, the outermost parts of the lens are not as sharp as the center. Human eyes are designed to work well with their pupils!

In fact, the 1964 Zeiss catalogue from which I got the picture at the top tells us something interesting. The reason 7×50 became the standard for nautical binoculars was not image brightness. It was because the oversize exit pupil made the eye's position uncritical. You could still get a good view while holding shaky binoculars on a rolling ship.

The exit pupil size is, of course, aperture divided by magnification; thus 7 mm for 7×50, 5 mm for 7×35, 8×40 or 10×50; and 4 mm for 10×40 or 12×50.

And what we astronomers have discovered is that we see faint deep-sky objects better with exit pupils far below the 7-mm maximum. I usually use a 2- or 3-mm exit pupil at the telescope. And if your eyes have any astigmatism at all, too large an exit pupil will blur the image.

With all of that in mind, and having tried out a lot of binoculars, I would recommend 10×42 binoculars as the amateur astronomer's most-used instrument. The ones I actually have at present are either side of that — 8×40 and 12×50. I think 10×42 is the "sweet spot" between image brightness, magnification, and — importantly — compactness and light weight. A close second choice is 8×40 or 8×42.

I've looked at a lot of good binoculars in these sizes in the under-$400 price range. Several quite good ones are under $200. The most intriguing are the new, entry-level Zeiss "Terra" products, 8×42 and 10×42, but these have many competitors.

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M4 with a definitely-not-cooled image sensor

The evening of June 15 was hot, but I wanted to test how well my AVX mount would track now that I've made further adjustments, so I took a series of 1-minute exposures of M4 through a 300-mm lens at f/6.3 and my Canon 60Da. No autoguider was used and no guiding corrections were made. Every exposure in this sequence of 15 tracked just fine. I set the lens to f/6.3 to rule out optical limitations so I could judge the tracking more precisely, and also to simulate the darker sky conditions at Deerlick, where I would use this lens wide open.

Here you see the bright star Antares at the left, the globular cluster M4 at the right, and the more distant globular cluster NGC 6144 above center. The dramatic rays on Antares are diffraction from the lens diaphragm.

The challenging part was the sensor temperature. The 60Da has no cooling built in, and the outside air was so warm that the sensor operated at 35 C (95 F). At that temperature, the noise level was rather high.

So how did I get a low noise level? By integer median downsampling. I used PixInsight to group pixels into 4×4 bins, then take the median (not the average) of each bin (thus rejecting extreme values). This turned my 18-megapixel camera into a very-low-noise 1.2-megapixel camera. With 15 exposures and 4×4 binning, I took the equivalent of 240 pictures, stacked; the noise level should be about 1/16 of its original value.

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The Ring Nebula at low magnification

Here is a similar picture of the field of the Ring Nebula in Lyra, flanked by the bottom two stars of the constellation itself. Stack of sixteen 60-second exposures.

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The open cluster IC 4665

This cluster is a striking sight in binoculars but is hard to photograph because it consists of a group of relatively bright stars without fainter ones. That may explain why it missed being included in the Messier (M) catalog and also the New General Catalogue (NGC). IC stands for Index Catalogue, a sequel to the NGC.

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A nebula so bright you'll miss it

For visual observers I want to recommend the planetary nebula NGC 6572, which I almost overlooked the first time I saw it in the 8-inch because it was so bright.

Bright, but compact. It looked like a star. At 140× I could see that it wasn't a star, but some observers might need 200× to be sure.

To me it looked slate-blue, not too differently colored from a remote but hot (blue-white) star. Others report a that it looks green to them, even "emerald green."

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Charleston

May light eternal shine on the victims of the Charleston massacre, the Methodist Bible study participants whose deaths may well constitute Christian martyrdom.

I would caution everyone not to jump to conclusions, and in particular, to maintain a clear distinction between what you know and what you imagine. Plenty of people have made up detailed scenarios in their own minds and are commenting publicly as if they knew exactly what happened and why. The rest of us are well aware that we do not know.

It was an act of terrorism, intended to intimidate many by killing a few; we don't know whether the shooter acted alone, or whether, even if he thought he was acting alone, he was in fact manipulated by others. As with any terrorist incident, I would also advise people to be alert for unusual reactions to it by others.

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A hot day indoors

Let the record show that for an unknown length of time up through the evening of June 16, probably including one or two full days previous, the temperature in my upstairs workshop area as 103 F (39.5 C). This includes the darkroom.

That's what happens when we go a couple of days without going upstairs! I'm sure the materials in the darkroom, already out of date, aged a year in a couple of days. I hope nothing else was damaged. Remarkably, the computer that we access remotely never had any problems.

The air conditioner is being fixed now.

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Canon lens technology makes astronomical history

I don't work for Canon; I use and often recommend their products, but also those of their competitors. Nonetheless, tonight's news is that Canon has helped make astronomical history.

I'm referring to the Dragonfly telephoto array of astronomers Roberto Abraham (Toronto) and Pieter van Dokkum (Yale), described more fully in this video (especially around the 30-minute mark) and this paper.

The astronomers are studying faint material on the outskirts of galaxies. They need to be able to photograph objects that are 1/10,000 as bright as the skyglow at a remote desert observatory.

And it turns out that skyglow isn't the problem. Digital image sensors have so much dynamic range that if the skyglow is uniform, it can be subtracted out.

What gets them is scattered light within the telescope. There are always a few bright stars in the field, as well as a lot of medium-brightness ones. In all ordinary telescopes, this light is scattered irregularly, but it goes unnoticed under ordinary imaging conditions.

Some of the scattering comes from the central obstruction of Schmidt- and Cassegrain-type telescopes. Observatory telescopes for photographing faint objects, such as the Sloan, have large central obstructions. The central obstruction means the light waves are disrupted by twice as many edges as they ought to. Diffraction isn't reflection or scattering; that's a physics lesson we don't have time for right now. But it does put more energy into the outer parts of each star image compared to the center.

What's worse, Drs. Abraham and van Dokkum found that all mirrors are slightly cloudy. Reflecting telescopes scatter light because the aluminum coating is never as smooth as light itself. This, also, is unnoticed under normal conditions, but their research needs weren't normal.

So they started thinking about things that amateur astronomers and photographers already knew: To photograph faint extended objects, what matters is f-ratio, not aperture. And the telescope should be made of glass. So what you need is a medium-sized f/2.8 refractor.

And f/2.8 refractors are abundant — but nowadays they're called telephoto lenses! Professional astronomers stopped using refractors for cutting-edge research about a century ago, but the camera industry kept advancing the technology. Now you can see superb refractors in use at every football game.

The icing on the cake is that Canon has recently developed sub-wavelength coating (SWC, SWSC) to reduce reflections from glass. It's vastly better than ordinary multicoating, and it allows a lens to have many elements without losing or scattering light.

So the astronomers chose the Canon 400-mm f/2.8 L IS EF II lens, which you can buy off the shelf for about $10,000. It's not cheap — my Canon 300-mm f/4 cost only a tenth as much — but it's far from the price of an observatory telescope. And look at those MTF curves! The third one is the one that matters. It shows a level of optical quality that leaves nothing more to be wished for. (The first two curves tell you how it pairs up with photographic Barlow lenses.)

Instead of just one, they bought several and put them on a single equatorial mount with good astronomical CCD cameras attached. (Sorry, Canon, this is a bit beyond a DSLR, even the 60Da.) They take multiple pictures of the same region at the same time, then stack them to combine their sensitivity. And the Dragonfly is growing — as funding permits, they are adding more lenses and cameras. The whole thing is installed at an observatory at a dark-sky site and is computer-controlled.

The result? Probably a series of discoveries about the outer regions of galaxies, with implications about how galaxies form, and maybe even the discovery of a new class of faint galaxies. Stay tuned for more.

Why this intrigues me is that it's the first time I can recall a consumer optics company advancing astronomical research (however inadvertently!) since Carl Zeiss more than a century ago. (Perkin-Elmer, important later on, isn't exactly a consumer optics company.) We've had several astronomical advances credited to the late lamented Kodak, but they were films and image sensors, not optics.

Maybe I've overlooked something, but this ought to be great PR for Canon. If I were their CEO, I would do two things: sponsor the Dragonfly project (which is currently completely separate from Canon as far as I know), and team up with a maker of observatory telescopes to bring out a line of serious research instruments with the Canon name on them and SWC on the glass elements.

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Telescope dedication, or commissioning, or something

Observatory telescopes often undergo anywhere from two months to a year of testing and adjustment before the official dedication and "first light" ceremony. The same is true of my Celestron EdgeHD and AVX mount, not because of anything wrong with it, but because much of the technology was new to me, I wanted to get to know it thoroughly, and the process was interrupted by factors ranging from bad weather to Melody's hospital stays.

Now, however, slightly more than a year after bringing it home, I hereby declare the telescope commissioned, or dedicated, or what you may call it. To mark the occasion I've attached a sticker quoting Psalm 19:1. This same verse has been on all my major telescopes since 1980. On my Celestron 5 it is in Latin; on my Meade it was in English; and on the EdgeHD it is in Hebrew and English.

In case anyone else wants to make the same sticker, click here for a Word file or here for PDF; each of these will print two of the stickers on a sheet of Avery 15513 white weatherproof labels. (I suggest editing the file to make other labels that are useful to you on the rest of the sheet.) And I have one unused sticker, which I will send to the first person who requests it.

Those to whom this is important will probably have already noticed that this Hebrew text does not contain the Divine Name.

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Appreciating the Baptist Center

Recent articles may have lulled you into thinking this is an amateur astronomy blog. Not so. Now for something completely different.

A large part of Melody's and my undergraduate leisure time was spent in the Baptist Center, a building at the University of Georgia built and sponsored by the Georgia Baptists. Yesterday we attended a reunion there. In what follows I'll say what I said to the group, but first, I'll give you some background information.

Wisely, in the 1960s, the Georgia Baptist Convention decided to spend its money on a building for students to hang out in at any time of the day — not just sending a campus minister to organize activities. The building was a place to go between classes, with a function similar to the student union building or a common room at a smaller college, or, for some people, a fraternity or sorority house (but with big differences which I'll get to). It had sofas, desks, a small library, Ping-Pong tables, and (in its heyday) daily lunch service. There were plenty of organized activities, but one didn't have to participate in them.

In so doing, they sidestepped at hot administrative problem forty years before it became hot. You've probably heard of recent controversies about the use of student activity fees to fund religious groups. Well, we registered the Baptist Student Union as a student organization (because the administration wanted us to) but consumed virtually nothing funded by activity fees. We had our own building and were self-sufficient, thanks to the generosity of the Georgia Baptists.

What was so great about the Baptist Center? Three things.

First, it gave us a Christian community within a secular university. The 1970s were when mid-century conformism bumped into late-century decadence, and for those of us who were "conscientious objectors in the Sexual Revolution," or just wanted to get away from the hard drinking and drug experimentation that were so common, the Baptist Center was a welcome refuge. It was a good place to make friends without being pressured to do anything unwise.

The experience was like going to a Christian college but with full access to a large secular university. It may have been better; every Christian college has sub-community of "rebels," but at the Baptist Center, if people didn't agree with our values, they simply left.

Many of us met our spouses at the Baptist Center. I didn't, but I brought Melody to it within eight hours of meeting her. For me, it was a university within a university. It was my native habitat, and I really wanted to know whether she would like it. (She did.)

Second, it required no time commitment. A person didn't have to go to any scheduled activities in order to be part of the community. Almost all "student activities" were time-eaters. This wasn't, or at least need not be.

On a more subtle level, people were friendly without demanding attention. For shy people like Melody and me, that was very welcome. So much social activity, of any type, requires commandeering someone's attention for a certain length of time and entertaining them. Hanging out at the Baptist Center didn't.

Third, it didn't much matter whether you were a member or not. There was a membership roll, but you didn't have to be on it. You didn't even have to be a Christian — we had several non-Christian hangers-on.

And there were no cliques and no differences of status between people. Everybody was equal. We usually didn't know who was rich and who was poor, who was doing well in school and who was struggling with grades.

The big difference between the Baptist Center and a fraternity or sorority is that there was no sharp distinction between people who were "in" and people who weren't. Nobody applied for membership and was voted in or out. The Baptist Center implemented something I've always believed in: the boundaries of a circle of friends should always be fuzzy.

[Added 2022:] For relatively shy people like Melody and me, the congenial crowd was much more important than the opportunity to make close friends. We weren't much into having close friends, except each other. What the Baptist Center gave us was a place where everybody there was reliable — could be trusted to respect us and not give us flak for our Christianity or for being serious about our studies. We had had plenty of those kinds of flak in high school.

So what did it achieve? The main purpose of the Baptist Center was not to make Christians but to keep them. Compared to more evangelistic student organizations, we had a much lower attrition rate; almost everyone is still a Christian 30 years later. (I do not know of even one person in my crowd who left the faith, although some did move to other churches, and one, through a convoluted path, is now an Episcopal bishop.) Let me hasten to add that I'm in favor of evangelism; it's just not the only kind of ministry. In fact, I think we led some people to Christ who would not have been receptive to a more hurried approach.

One last note. The intellectual level at the Baptist Center was rather high. It certainly wasn't a place to hide from intellectual challenges; on the contrary, the combination of a Christian community with a secular university was enriching. Several of my crowd became professors in various fields.

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Astigmatism-correcting eyepiece

My last visit to the eye doctor resulted in no change to my glasses, so I decided to treat myself to an astigmatism-correcting eyepiece. To be precise, I got a Tele Vue 32-mm Plössl with a Tele Vue DioptRx astigmatism corrector.

This is part of my general move toward observing without eyeglasses. For decades I almost always wore glasses at the telescope. That's not ideal because eyeglasses aren't multi-coated (mine are single-coated) and because you have to keep three things centered and aligned — the eye, the eyeglass lens, and the eyepiece. Optical quality always suffers a little. The astigmatism-correcting eyepiece simplifies the system.

If my eyes didn't have astigmatism, any eyepiece would work perfectly without glasses; I'd just have to focus it differently than the average person. Focusing can completely overcome nearsightedness and farsightedness. But I have just enough astigmatism in my right eye to be noticeable.

About astigmatism: Astigmatism is what happens when a lens has more refractive power along one axis than another. Consider using a glass rod as a magnifier. It only magnifies in one direction; it has severe astigmatism. (In fact it has nothing else.) Most astigmatism isn't that severe; instead, what happens is that the lens has elliptical rather than circular symmetry. Imagine making a lens out of clear rubber, then grabbing it at two points diametrically apart and pulling. That would give it astigmatism.

Another way to give a lens astigmatism is to change one of its spherical surfaces into a surface more like that of an American football or a rugby ball. That's called "adding cylinder power" and is how eyeglass lenses are made to have astigmatism opposite that of the eye. Eyeglasses to correct astigmatism were invented by the astronomer G. B. Airy.

In the human eye, astigmatism can result from uneven stretching of the lens, or asymmetrical curvature of the cornea, or decentering of the lens relative to the cornea, or miscellaneous uneven growth.

On an eyeglass prescription, astigmatism ("cylinder") can be reckoned as either positive or negative lens power to be added to the spherical (non-astigmatic) power of the lens. Depending on which is chosen, the axis (direction) of the astigmatism changes 90 degrees, and so does the spherical power to which it is added. Optometrists measure it as negative; opthalmologists, as positive.

To order the Tele Vue corrector, all you need to know is the strength of the astigmatism. It doesn't matter whether your prescription says +0.75 or -0.75, for example; they are the same. You don't have to specify the spherical power because you make that up by focusing the telescope. Nor do you have to specify the axis because you get to rotate the corrector yourself to find the best position.

My astigmatism had been measured anywhere from -0.50 to -1.00 over the last several eye exams, not trending in any particular direction, just randomly jumping around. I figured 0.75 would be a good guess for its average value, and I was right.

So what's it like? The corrector attaches to the flange that would normally hold the rubber eyecup on any of many Tele Vue eyepieces; then it has a rubber eyecup of its own. It rotates freely and is quick to take off and put on, so if a non-astigmatic person wants to look through the telescope, I can accommodate them.

In use, what you do is rotate the corrector to get the sharpest image. One useful tactic is to throw a bright star slightly out of focus, then adjust for the roundest image. The telescope must be perfectly collimated, of course, and the star must be at the center of the field. Miscollimation causes astigmatism in the telescope, and all telescopes have some astigmatism away from the center of the field.

I did another thing: indoors, I took off my glasses and tried reading through the corrector lens, rotating it until I got the sharpest view. Then I put a piece of white tape on it to mark the direction that is directly downward (toward my chin). This agreed with the best position for it at the telescope, and of course I have to turn it when the telescope changes position, so it's handy to be able to feel the piece of white tape in the dark. Note: All of that was a mistake. The lens rotates relative to the A-F scale whenever you attach it to an eyepiece, and maybe also at other times. Ah well... Click here for the correct solution.

The result? The corrector adds some extra crispness to an image that I was accustomed to viewing without it. I didn't quite know what I was missing. The benefit is quite noticeable with exit pupils 3 mm and larger. With a 1.5-mm exit pupil on a different eyepiece (which will soon have its own corrector), the effect is more subtle but still there.

The human eye with astigmatism is not a precision instrument, and you should be aware that your astigmatism may not be the same at night, with a wide pupil, as in the daytime.

You may even find — as I did — that your astigmatism is not symmetrical. Viewing a point source out of focus, a normal eye should see a round image (even if nearsighted or farsighted) and an astigmatic eye should see an elliptical image. With my right eye, what I see is shaped like a chicken's egg. That explains why it comes out different in different eye exams — it depends on whether they're matching the big end or the small end of the egg! The departure from ellipticity is slight, and I get better than 20/20 vision with proper eyeglasses, so it's not a problem. If it were, laser corneal surgery could correct it.

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How to hold binoculars steady

Photo by Sharon Covington

I've just learned something about binoculars that normal people probably learn the first time they ever use them.

All these years, I've used binoculars and telescopes with my eyeglasses on. That has some disadvantages, and now I'm changing my practice.

Not all binoculars will focus to infinity with my rather nearsighted eyes (-5 in the left eye, -4 in the right). But some will.

Here's what I learned: The eyecup, resting in my eye socket, helps hold the binoculars steady. All those years, this is something I was missing because it can't be done with eyeglasses. Not only are the binoculars steadier, the remaining movement doesn't move the eye out of the exit pupil, so the movement is much easier for the eye to track.

To hold the other end of the binoculars steady, I learned long ago to stretch my fingers out so they are more sensitive to changes of angle. Don't grip the binoculars tightly with clenched fists — support them with fingers stretched along their length.

Anyhow, now that I can use the eyecups like a normal person, the binoculars are much steadier and I am enjoying cruising around the sky with a pair of 12×50 binoculars that I previously considered too hard to hold steady.

The eyecup must have been the key to using old-fashioned handheld telescopes, too (thank you, Lord Nelson) — it must have provided an essential support. I can't imagine using a 30× nautical telescope steadied only by my hands.

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M65

The galaxy M65, a stack of five 148-second exposures taken on May 23. 8-inch Celestron EdgeHD with f/7 reducer, Canon 60Da, ISO 1250.

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M66

The galaxy M66, a better-processed version of the picture I posted last month.

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M51

The galaxy M51 and its companion, a better-processed version of the picture I posted last month.

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I'm back...

After a 5-day hiatus, I'm back, and I haven't been out of town, just busy. What's more, I have enough Daily Notebook material to fill many pages, but not all of it will appear today.

The picture of "my" galaxy M102 (below) has been redone again as I keep finding better ways to process images with PixInsight. Several more re-done pictures are on the way.

I've also written about the right way to do Celestron All-Star Polar Alignment.

Now for today's new material...

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M104

This is the Sombrero Galaxy (M104), one of the brightest galaxies viewable with a small telescope. Take on the evening of May 23, this is a stack of twelve 148-second exposures with a Canon 60Da at ISO 1250 on my Celestron 8-inch EdgeHD with f/7 compressor. This is a small part of the image, enlarged.

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Saturn

On June 4th I got the 8-inch out again for an equipment-testing session, but I didn't come back entirely empty-handed; here's Saturn in full color and in infrared. Each of these is the stack of the best 80% of about 1300 video frames with DFK and DMK cameras respectively, at f/30.

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What I have learned about spray-painting

[Updated.]

Having had occasion to spray-paint several small objects recently, I went to manufacturers' web sites and reviewed some of the advice they give out. Based partly on that, and partly on my own experience, here are some tips. I don't claim to be an expert, but what you see here is more information than is written on the average paint can!

(0) Spray paint dries very fast and is best applied in many thin coats, which can be in fairly rapid succession. They don't have to dry completely, but you want enough drying to take place that the paint will not run. Five light coats at ten-minute intervals are often practical. The first coat should be very light. Follow directions about re-coating intervals; when you re-coat enamel paint, the previous coat must be either fresh enough to still have some "tack," or absolutely totally cured. (Dupli-Color says to recoat their enamels within 1 hour or after one week. Krylon and Rust-Oleum are more permissive.) Lacquer paints permit re-coating at any time.

A full paint job with spray automotive lacquer could take one coat of primer, eight coats of paint, and three or more coats of clearcoat. This is not as time-consuming as it sounds.

(1) Above you see how the spray pattern should traverse a rectangular object that you're painting. The spray can must not pause or back up during a pass; you have to be willing to waste paint, moving completely off the object at the ends of each row. (This is something that took me a long time to catch on to.)

(2) Rows should overlap about 1/3. This implies that the top and bottom rows will be partly off the object, since the second row should just reach to the top edge, and the next to last row should just reach to the bottom edge. That way, all parts of the surface get equal amounts of paint.

(3) Krylon actually recommends that you let go of the button while turning around at the end of each row. This reduces the risk that you'll accidentally spray too much paint on the object while doing so.

(4) Always test the paint on a scrap of cardboard or something, to make sure you have the technique right and the paint is spraying freely. If the paint has been on the shelf a year or two, shake it for three minutes after the steel ball starts moving, and then test it carefully.

(4a) [Note added 2019] Spray from the correct distance (usually about one foot). Paint dries while in flight from the can, and if you spray from too far, it will stick poorly and be powdery; if you spray from too close, it will be runny.

(4b) [Note added 2019] Wear safety glasses over your eyeglasses even if your regular glasses are safety-certified. Keep the paint off them! A fine powder of paint can stick to your eyeglass lenses and not be noticed until it's too late to get it off.

(5) Never paint a shiny surface if you can avoid it. Metal should be roughened with fine sandpaper. Plastic, believe it or not, should be wiped down with mineral spirits (to remove the waxy plasticizers that are put in at manufacture). (Painting plastic also requires suitable paint or primer.) Also don't paint over old paint, which may not be adhering well.

(6) I find primer very useful and strongly recommend it. Unlike ordinary spray paint, it builds up thick enough to smooth a surface, and it sticks well to metal. Primer plus clear acrylic may be all you need on a piece of machinery. Use enamel clear coat over enamel, lacquer clear coat over lacquer; do not mistmatch them.

[Note added 2017:] Aluminum is hard to paint because it forms an invisible but tough oxide coating within 15 minutes after being sanded. Sand it and immediately prime it, preferably with aluminum primer. Wet sanding with #400 sandpaper is recommended.

Self-etching primer sticks especially well to metal but cannot be used as the only coat; it is acidic and not tough.

(7) If you need paint that really sticks to metal, try slow-drying appliance epoxy. Only a few colors are available, unfortunately. You have to apply all the coats within half an hour and then leave the painted object untouched for 24 hours; preferably, give it a whole week before heavy use.

Automotive-grade lacquer is also, in my experience, better at sticking to metal, and also harder after it dries, than general-purpose enamel spray paint.

(7) If the surface is going to be touched or handled much, I apply several coats of clear acrylic, which, like spray paint, dries very fast. It has a granular texture and does a very good job of hiding variations in texture in the underlying paint.

(8) Distinguish lacquer from enamel paints, and do not apply lacquer over enamel unless the enamel is very fully cured (weeks or months old). See these further tips from Dupli-Color.

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M102 redone

I'm back, albeit very busy. Lots of things are planned for the Daily Notebook, but my consulting business is booming, and some things will have to wait. Over the next few days I'll unveil several new astrophotos, as well as better-processed versions of old ones.

This is an example of the latter. Here's "my" galaxy again — I'm told my article about it in Sky and Telescope will be coming out in about three months. This is the picture I posted a few days ago, but processed differently. Instead of using superpixel mode, I used conventional de-Bayerization and then downsampled the image to half the original size. (And further, before it got to this page, which won't accommodate 18 or even 4 megapixels!) And then I re-did it again on June 7, with better noise reduction.

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Moon in EdgeHD

The 8-inch EdgeHD telescope with f/7 compressor is surprisingly good for taking pictures of the full face of the moon. Well, not quite full. The entire round moon still won't fit in the field of a camera with an APS-C sensor. At least not all the time; it's OK when near perigee. I wish they had made an f/6 compressor instead.

This is a single still picture, only slightly sharpened digitally.

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