Michael A. Covington    Michael A. Covington, Ph.D.
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Daily Notebook

Popular topics on this page:
Here come the under-$200 PCs
Focusing error can mimic guiding error. How?
A call to conscience about gossip on Facebook
Integer gear ratios in telescope drives
Answer that thing, or turn it off!
Comet Lovejoy C/2014 Q2
Comet Lovejoy C/2014 Q2
Comet Lovejoy C/2014 Q2
Comet Lovejoy C/2014 Q2
Comet Lovejoy C/2014 Q2
Moon (gibbous)
Mercury and Venus
Witch Head Nebula (IC 2118)
Orion Nebula (M42)
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Answer that thing, or turn it off!
Etiquette for 2015

"Ping!" "Bong!" "Da-ding!"

All of a sudden, a surprising number of people emit those sounds at random but short intervals from on or about their person.

They are signals from a smartphone, indicating that a text message or e-mail has come in, or maybe just that someone in North America has posted something on Facebook.

And they're rude.

The only reason to use audible notifications is that you are actually expecting a message important enough to warrant your immediate attention. I don't mind if when your phone rings, you excuse yourself and answer it. That's reasonable.

It's equally reasonable to excuse yourself to check an incoming text message. Provided, of course, you are taking care of real responsibilities, not just rudely turning away from people who are talking to you in order to surf the Web.

But if a "ping" isn't important enough to justify interrupting the people around you, then it shouldn't be heard at all. Don't leave your smartphone "pinging" just to show us that you are getting more text messages than you can condescend to look at.

And don't set it to "ping" whenever anything new appears on Facebook, or whenever a snowflake falls in Montana. I think the two are about equally frequent, at least in the winter.


Integer gear ratios in telescope drives

Today, a short, very technical note.

One of the selling points of the Celestron AVX telescope mount is that it has "integer gear ratios" in the gearbox between the motor and the worm gear.

When I first heard this, my first thought was, "Isn't a gear ratio always the ratio of two integers? You can't make a gear with π or √2 or even 2.8 teeth."

What they mean is, the gear ratios are always 1:n where n is an integer. Not just m:n.

And what it buys you is that the gears mesh on the same teeth every time they go around. If a gear ratio is something like 27:51 or even 2:3, the gears will not mesh on the same teeth on consecutive cycles. It will take them several cycles to get back to the same teeth meeting each other.

Ordinarily, ratios like 27:51 are preferable because they spread out the wear on the teeth. (A burr won't keep hitting in the same place.)

But if you are using periodic error correction (PEC), you want integer (1:n) gear ratios so there will be no periodicities slower than the rotation of the slowest gear, which, in that situation, is the worm gear. When the worm gear completes a rotation, all the smaller gears will be in the same positions as when it started. Every cycle will be exactly alike, and its irregularities can be recoded and corrected digitally.

(An integer gear ratio doesn't mean that one gear has only one tooth, of course. A ratio of 30:90 is perfectly good because it equals 1:3.)

All this has become important as improvements in worm gears have led to the discovery of other sources of error. For example, the Celestron CGEM has a perodicity of 8/3 worm gear revolutions that becomes noticeable when the main periodicity (of 1 worm gear revolution) is corrected.

There is no way to correct a periodicity longer than the worm gear period using conventional one-cycle periodic error correction. The best you can do is average several cycles of the worm gear (which is a good idea anyway, to eliminate random noise). Then you are steadfastly ignoring the periodicity that you can't correct.

The alternative is to use a periodic error correction cycle that spans enough worm gear cycles to complete the longer cycle that is causing trouble.


In praise of easy, non-competitive astrophotography

This isn't exclusively an astrophotography blog, although this month, it has nearly become so. While at home with the flu, I've read a lot of Rod Mollise's published online material. He makes much of a point that I also want to emphasize:

Your astrophotos don't have to be the best in the world in order to be worth taking. There will always be amateurs who get better pictures than you do. The Hubble Space telescope will always get better pictures than they do. And so on.

Every time I set up the camera, I get pictures that would have been prize-winners thirty years ago. In the 1985 first edition of Astrophotography for the Amateur, a contributor's tiny cooled-emulsion image of a galaxy with spiral arms was presented as an example of very advanced work — which it was. Today, I can do better than that with a DSLR and a telephoto lens in just a few minutes.

Meanwhile, others with Astro-Physics mounts, huge refractors, and time to do 14 hours of total exposure are at the vanguard — their pictures win prizes and mine don't. They even discover uncatalogued nebulae.

(There! That's what I want for a retirement achievement — my own nebula! It's not impossible; what I'd need to do is repeatedly photograph a field that has a lot of interstellar gas and also variable stars, to see if something pops up into visibility that hadn't been noticed before.)

Let me suggest a better reason for taking astrophotos: not because they're the best in the world, but because they're yours. If you go to Yosemite Park, don't you snap a picture of Half Dome, even though Ansel Adams made a much better one many decades ago? The same goes for every famous landmark you've ever seen — top-grade professional pictures already exist — you're taking a picture for the satisfaction of doing it yourself and because it records your experience.

That's why I think there will always be a place for snapshot astrophotography. By that I mean, not literally snapshots (at least not yet), but pictures that are sufficient rather than outstanding. They are competent and lack major technical flaws, but they don't break new ground. They are souvenirs of your experience exploring the sky.

And here's a secret. Professional astronomical research is more like snapshot astrophotography than competitive art photography. Professionals almost always want a picture that is just good enough to show clearly the thing they're concerned about. There's a sense of economy. They're always working near their instruments' limits, and the goal is not usually to produce a thing of beauty, but rather to answer a question.

Not that I'm against producing things of beauty, of course! I just want to emphasize that there's a whole range of worthy motives for, and levels of, amateur astrophotography.

Flu report: It's remarkable how fast Tamiflu works, even when started "too late." My fever is gone, but I still have a sore throat and cough and need to rest up. My usual rule of thumb is to stay home and rest until I'm sure I've stayed one day too many, then resume work. Unfortunately, there will be no spare time for the next few weeks because I'll need to catch up!


The history of my telescopes

I'm still too sick to work, but reading Rod's encyclopedic descriptions of telescopes has inspired me to write down a checklist of the telescopes I've owned and used. This is from memory, without checking logbooks.

Tasco 40-mm variable-power erect-image refractor on tabletop tripod. Early 1969. This might be described as belonging to the prehistory of my amateur astronomy — I was motivated to learn the sky but did not actually use this telescope much. I still have it. It has surprisingly long eye relief and I'd like to see what can be done with it.

Tasco 9TE refractor, 60 mm f/11. My first serious telescope, which my mother gave me for Christmas in 1969. I used it very satisfyingly, especially after adding a 25-mm Ramsden eyepiece. Sold it in 1974.

Criterion Dynascope RV-6 6-inch f/8 Newtonian. My first really serious telescope, which I used from September 1970 until moving to Athens. Finding that I was busy with other things, I got away from astronomy for a while in college and sold the telescope in 1975.

Driving back from Watson's Mill State Park with Melody in August of 1979, as we looked at Venus in the sunset, I decided I wanted to get back into amateur astronomy, and that led to...

Coulter CT-100 4-inch f/3.5 Newtonian. This is a curious instrument that I need to blog about. It was my mother's Christmas present to me in 1979 (ten years after the Tasco) but was fraught with problems. The manufacturer couldn't deliver it on time, and I first took delivery of it without eyepieces, although it relies on the eyepiece to have a helical focuser. Performance was disappointing but I logged more than half of the Messier Catalogue with it.

I knew what I was getting into; having been an avid photographer all along, I was already very much an optics geek. It was a very special-purpose instrument, and it more or less served its purpose.

It transports more compactly than you can imagine. I'm going to get it out and write about it soon. Its biggest failing is simply that an f/3.5 mirror does not work well with any eyepieces that were affordable (or even had been invented) back in the 1970s. Later on, Coulter switched to an f/4 mirror. If I can rig a way to use it with a good Radian eyepiece, I might have something... There is also the matter of a finder.

Celestron 5 5-inch f/10 Schmidt-Cassegrain. Purchased in 1980 with help from Orion Telescopes (Santa Cruz, California), which gave excellent pre-purchase technical support, this was my main instrument for a long time and I still use it often. It is a classic "orange-tube Celestron."

Meade 2080-LX3 8-inch f/10 Schmidt-Cassegrain. Purchased in 1987 from the local Wolf Camera, in whose showroom it had stood for months. This served me well for several years and actually had its optics replaced by Meade due to coatings coming off (a notorious problem with some early Meades).

Celestron Celestar 8 Deluxe 8-inch f/10 Schmidt-Cassegrain. I got this in the 1990s for doing some writing work for Orion Telescopes and sold the Meade. Why I thought the Celestar would be better, I'm not sure. It did seem to have better optics, but the stepper-motor drive was subject to vibration (a problem Rod Mollise notes in one of his books).

Meade LX200 8-inch f/10 Schmidt-Cassegrain, computerized. This was my workhorse from 2000 until this past May; a very good telescope, but heavy.

This telescope is tied up in the estate of Tim Nix, of Camera Bug, who was selling it for me on consignment. I hope to get it back soon and find a new owner for it. One option might be to sell just the tube assembly, which is in excellent condition and has nothing hard to repair. The computerized base works fine but will be unrepairable in a few years if it fails.

Celestron NexStar 5 5-inch f/10 Schmidt-Cassegrain, computerized. I owned this briefly in 2000-2001 while working on my computerized telescope book. A nice telescope with one conspicuous design flaw — if you screw a bolt into its threaded mounting holes too far, you can do internal damage. (The hole doesn't have a bottom!) I actually did this and had to have Celestron fix it. After a while I sold the telescope, sans tripod and case, for as much as I had paid for it, including tripod and case. I use the tripod with the Celestron 5.

Celestron EdgeHD 8-inch f/10 modified Schmidt-Cassegrain on computerized AVX mount. The current workhorse. Much of the time, the mount carries my camera without the telescope. But the telescope is excellent, a real step forward from the conventional Schmidt-Cassegrain design.


Cough, cough!

Well, yesterday we were going to make a road trip to meet the new grandsons. For two reasons, we didn't.

One reason is that the weather was turning bad — we would have been driving in snow that wasn't forecasted until the very day it happened. There were also major wrecks in Atlanta and another city on our route.

But the main reason is that I got sick. In rapid succession, I've had a sinus infection, a flu-like high fever that lasted only a few hours, and, now, a cough, which I hope will not linger very long.

Too tired and sick to work, I'm occupying myself by reading Rod Mollise's blog about amateur astronomy, especially telescopes. He is convincing me that, several times over the decades, I have made very good choices of equipment. There were a lot of things on the market that didn't quite work, and I avoided them!


Short notes

The alert reader will surmise, correctly, that I've gotten busy. Don't worry; the Daily Notebook will rev up again soon. In the meantime, if you're interested in astronomy, let me suggest browsing through early 19th-century issues of the Monthly Notices of the Royal Astronomical Society. Lots of interesting things there, including (in 1836-37) Baily's Beads and the first determination of a stellar parallax.

On a totally different topic, to which I plan to devote a lot more space later, should churches ban traditional church music? That sounds like a bizarre idea, but it's the practice at at increasing number of Baptist churches — they switch over to "contemporary-style worship," which means that the music is accompanied by a pop-style band (not an organ or piano) and has all been composed within the past 10 years.

My concern is not the presence of new music; some of it is very good (although plenty of it isn't). My concern is abandoning centuries of Christian hymnody to "bring in the young people." And make them into permanent adolescents who will never learn the value of anything not on the current Hit Parade? Only an immature person thinks previous generations didn't know anything worth knowing. And the young people that I talk to don't want to be immature.

By the way, occasionally throwing in one older hymn, performed as a rock arrangement, is not enough. If 90% of the music reflects the most recent 0.5% of church history, I don't think you've struck the right balance.


Comet Lovejoy again

Here's last night's catch, a stack of 46 (yes, 46) 30-second exposures with my usual setup (Canon 60Da, 300-mm lens at f/5, AVX mount). The second copy shows it in black and white with higher contrast.

See the web site of Sky and Telescope's web site or any other major astronomy magazine for maps that will tell you how to see the comet yourself. It's easy to see in binoculars and is just on the verge of naked-eye visibility in town.


Mercury and Venus

One thing we need to teach our children is what planets look like in the sky, so that they don't think all planets are discoveries of the Space Age or even the telescope age.

Planets look like stars that move relative to the other stars. You can't see them moving, of course, but the movement is noticeable over the course of days.

Some people don't realize that Mercury, Venus, Mars, Jupiter, and Saturn were known in ancient and even prehistoric times because people noticed the movement. The very word "planet" is Greek for "wanderer."

Mercury and Venus are close to the sun, so we never see them high in the night sky. Currently they're putting on a show in the twilight after sunset; Venus is the bright "evening star" and Mercury is next to it. Here's what they looked like on January 10, when they were closer together than now. Fixed-tripod exposure with Canon 60Da and Sigma 105-mm lens, cropped.

Right now, the brightest star in the late-night sky, high up, is Jupiter. I'll start photographing Jupiter soon.


Pleiades again

The Pleiades star cluster is one of my favorite objects to photograph to verify equipment function, sky conditions, and the like. This picture of the Pleiades is comparable to my latest picture of Comet Lovejoy (below), but it's a stack of only 12 30-second exposures (which affects noise level, not brightness).

You can see plenty of reflection nebulosity (dust around the stars). Comparing to the comet picture that I posted yesterday, you can see that, at least roughly speaking, most of the comet's tail is considerably fainter than the nebulosity. That gives us a quantitative indication of how bright it is. Some people have taken pictures showing the Pleiades and the comet together, such as this one, by Gabriel Vasquez Lopez (posted on Facebook).


Comet Lovejoy at its brightest

Now back to astronomy. Today (January 16) may be the best view we're going to get of Comet Lovejoy, although it's going to remain visible for a while. Here is a stack of 22 (yes, 22) 30-second exposures with a Canon 60Da and Canon 300-mm f/4 lens at f/5, processed with DeepSkyStacker, which separated the comet from the starry background, stacked the images separately, and recombined them, thereby concealing the rapid orbital movement of the comet.

Here is a higher-contrast rendering that shows more of the tail, but also shows a lot of camera noise:

That tail is faint, much fainter than the reflection nebulosity in the Pleiades — but that's tomorrow's picture.


A call to conscience about gossip on Facebook

[Revised and extended, then edited for conciseness.]

One of the most frustrating things about Facebook, to me — the thing that may make me give up Facebook altogether — is the way otherwise intelligent people spend so much time spreading unconfirmed rumors or even blatant falsehoods. This happens in other Internet forums, too.

The game is, "If you don't spread what I'm spreading, you're not a loyal friend, and you might not even be a good person."

I won't play.

I see four main kinds of gossip:

  • Personal gossip about individuals. Fortunately, I don't see much of this, but some people engage in it incessantly. It's just as wrong on Facebook as anywhere else. I don't take about people unless they're either present in the conversation or already in the public eye.
  • Political gossip. This consists of saying that a politician said something evil or supports something evil, or that something scandalous is going on, and the major news media aren't reporting it, so it needs to spread as a "meme" (mini-poster) on Facebook, often with a link to a web site that looks like a major news source but is actually something we don't know anything else about.

    It is often very shallow and far-fetched. A politician is shown waving hello to someone wearing a turban, and that "proves" he's secretly an ISIS agent. Or people give you made-up facts such as "Congressmen get a $179k pension for life" (they don't).
  • Medical and health gossip. This works the same way, except that the claims have to do with health, often nutrition, and are often designed to torpedo a particular commercial product. Did you know that Splenda accumulates in your kidneys and poisons them? Well, it doesn't, as far as I can find out, but there's a Facebook "meme" that says it does, and it must be true because the lettering on it looks very professional!

    Made-up names of medical institutions are common in this kind of gossip. Who is to know whether the "Chicago Kidney Institute" is reputable? It's a name I just made up. (If there really is something by that name, I know nothing about it.) And gossipers don't stop there — they often cite real institutions and real scientists who never said the things they are being credited with.
  • Economic gossip. This is less common and involves giving people misinformation to act on. "Did you know CIA and NASA economists say...?" Wait a minute. NASA economists? Somebody's selling something — maybe worthless stock, maybe Ponzi schemes — and wants to recruit the gullible.

Particularly with political gossip, many people's goal is, "Spread whatever makes my side look good or makes the other side look bad, whether or not it's true."

And that's wrong. Spreading falsehoods or probable falsehoods, even to help the "right" side, is wrong. If you do not understand this, you do not adequately know right from wrong. You're operating at the level of tribal loyalty rather than truth and reason.

That includes misrepresenting people by quoting them out of context, a regrettable practice that I can only classify as a form of lying.

Of course, sometimes there's information that deserves attention even if it can't be confirmed, such as new discoveries or emerging scandals. But in that situation, you have a duty to be honest about the level of evidence that supports your claim. Don't take something as proven just because some activist web site (that you never heard of before) reports it.

And check facts in Wikipedia and Snopes. Even if they're not accurate, they will tell you if something is controversial. Of course, people wanting to deceive you will tell you, first off, that you can't trust reliable sources. "Don't believe Wikipedia. Don't believe Snopes." I reply: Wikipedia and Snopes are certainly fallible, but if you say they're wrong, I want to know exactly what they got wrong, and where to get better information, and why I should believe that your source is better.

It won't do to insult me just because I didn't believe an unconfirmed piece of gossip that supports your side on a political controversy. (Especially if I actually am on the same side as you politically, but am more scrupulous about facts!) Someone did that to me last night, thereby claiming the intellectual low ground.

I want to thank more than 40 people who have already expressed their support for this message, and several who have shared it on Facebook. A few afterthoughts...

I think sometimes the video game illusion is at work. Some people think that what they see on the computer screen is just a game, a fantasy world, and truthfulness about the real world doesn't matter.

For others, discussion is too much like sports fandom — just cheering one side and booing the other, complete with "trash talk."

I've heard people defend fabricated quotes and misrepresentations by saying, "Well, that's what he would say!" or "You just know he wants to say that!" Falsch. We live in the real world, where claims of fact are true or false. I'm not interested in how politicians behave in your imagination.

Remember that you can harm people by passing along bad medical advice. I've even seen people share dangerous "household hints" such as mixing bleach with acid (kaboom! or maybe cough, cough, phew!). If you don't personally know that something is wise advice, don't pass it on.

And you can harm your country by taking a good political idea and mixing it with so much foolishness that everyone thinks it's stupid. You are handing victory to your political opponents when you circulate nonsense that is supposed to support your side.

As an American with conservative leanings, I'm particularly sick of the sneering and sniping at President Obama that some people spout constantly. We need intelligent, informed criticism of his politics. We do not need fabrications, deliberate misrepresentations, and other displays of foolishness and bad faith. That stuff quickly convinces the audience that Obama's critics are intellectually bankrupt and have no real criticism to offer. It's giving conservatism a bad name.

Then there are the thinly disguised racists who despise Obama but can't quite say why. They flit from one vague, unproven insinuation to another, circling around the notion that there's something wrong with his nationality, religion, or parentage. It's fairly clear that their real objection is to the color of his skin. To them, I can only say, "get outta my face." I believe in equal rights and respect for all human beings regardless of color. And although I did not vote for Barack Obama, I respect him and the millions of people who did.


Revised DSLR astrophotography notes

No Notebook entry today; instead, click here to see major revisions to my "New DSLR notes," which are notes about DSLR astrophotography since my book came out in 2006.


Focusing error can mimic guiding error — but how?


These three pictures of the center of M42 seem to illustrate guiding problems. The middle one has nice, sharp, round star images (and also shows more faint stars); the other two images are slightly trailed in different directions.

But, in fact, guiding was not the issue. Each exposure was only 2 seconds and was replicated several times.

The difference between these pictures is focus. The lens (Canon 300/4 at f/5) was focused a bit differently for each of the three.

Unlike telescopes, camera lenses are not ordinarily diffraction-limited wide open. Rather, correct focus is the point at which several aberrations come nearest to balancing each other out. And, because of finite manufacturing tolerances, one of the aberrations is astigmatism, caused by slight errors of centering.

That is what you are seeing here. If astigmatism is present, an out-of-focus star image is slightly elongated one way or the other.

When a star image is perfectly in focus, the astigmatism isn't visible; it's hidden under the effect of the other aberrations and diffraction.

This lens has a detectable imperfection, but that does not make it a defective lens. When focused carefully, it produces round star images less than 0.01 mm in diameter, corresponding to a resolving power around 100 lines per mm, depending on the point spread function, which I did not measure. That is good for any lens, and exceptional for a telephoto; in film photography, it would have meant that the resolving power would always be limited by the film, not the lens. But digital sensors are sharper than film, and astigmatism is one of the aberrations that we see when this lens is slightly out of focus. The other is chromatic aberration.

Notice also that at best focus, there is a bit of purple fringing around the stars from residual chromatic aberration. The different aberrations of this lens don't all balance out at exactly the same point. Accordingly, focusing this lens for minimum chromatic aberration isn't the right strategy. It's sharper if some chromatic aberration is tolerated. If it bothered me, I could add a pale yellow filter to get rid of it, but as it is, a small amount of chromatic aberration helps make the brighter stars stand out.

So — if, like me, you are beset by a tracking problem you just can't seem to eliminate — check the optics, and try refocusing!

Subsequent spooky development: After reproducing this problem with the same lens in one subsequent session, I was unable to reproduce it in the next session. The star images were always round! Maybe something got out of alignment and then worked its way back into place. Or maybe there was a problem with the way the lens was attached to the camera body. Who knows?


Comet Lovejoy C/2014 Q2

I am happy to say that Comet Lovejoy has achieved naked-eye visibility (at least to my rather trained eyes) even under the incompletely dark skies of Athens, Georgia. It should be easy to see out in the country.

The pictures you see above are black-and-white presentations of a stack of seven color exposures; I'm still working on the processing technique. Canon 60Da, AVX mount, Canon 300/4 lens at f/5, each exposure 30 seconds at f/5. The second rendering has artificially high contrast and is full of noise and camera artifacts, but it shows that the comet has quite a tail. If I had realized the tail would extend outside the picture, I would have used a wider-angle lens.


Am I un-suit-able?


I just went shopping for a new suit, as I do every fifteen years or so whether or not it's urgent.

Cartoon by Sharon Covington...

I found that a lot had changed in fifteen years. My previous suit was made-to-measure through the late lamented George Dean's Men's Shop, which is out of business, as is its closest competitor, George Gibson's. Fortunately, the third one, Dick Ferguson's, lives on, and I could get a made-to-measure suit there for about $850 with one pair of trousers, $1150 with two. That would be worth doing if I needed it a little more than I do.

Off-the-rack is a different story. I'm hard to fit. What I mean is, I'm not Size 38, which seems to be the standard in this town. I'm told that other towns are different, but Athens is dominated by young college men. I'd do better in a town with an aging population. I'm told that short people (which I am not) should go to Albuquerque because people with Hispanic or Native American heritage are often short, unlike the lanky Scots who settled North Georgia. And, apparently, if you like long-rise trousers (as I do) you should go to England.

Seriously, my jacket size and my trouser size don't normally come together, and never have. Fortunately, Jos. A. Bank was able to fit me with matching separates. They even have long-rise trousers.

The other thing that has gone the way of the dodo bird is free alterations. I ended up buying the suit unfinished (unhemmed) at more than 60% off list price, and taking it to their recommended tailor, whom I will pay separately. Even so, I got out for less than half the price of made-to-measure. Ferguson's doesn't have free alterations either, as I found out when I bought a jacket from them the other day.

I don't normally wear suits. Like most college professors since maybe 1500 (I'm kidding, I mean 1920), I wear a jacket and contrasting trousers. On suit-and-tie occasions I just add a tie. This is good enough for academia, but some very formal occasions still require a suit.

And suits are taking their place among formal wear, like tuxedos. You can already rent them from formalwear places (a fact worth knowing if you're traveling and your good suit gets lost or damaged!). The personally-owned business suit, outside the financial and legal professions, may not be common for much longer.

Among those who do own suits, made-to-measure may become more common and cheaper. Nowadays, suits aren't made by rooms full of tailors — they're cut out by computer, using numerical control. Dial in the measurements, and the machine makes a custom suit. Already ModernTailor and IndoChino are selling made-to-measure suits through the Internet. Long gone are the days of putting down a deposit at Moss Bros. and coming back a year and a half later for your "bespoke suit" — even the Moss Bros. now do their magic in eight weeks.

One last note. When a store has 60%- and 70%-off sales, as Jos. A. Bank does, I begin to believe that the list prices are fictitious. That is an old game that I don't particularly appreciate.

While shopping, I learned that the Radio Shack at Georgia Square Mall is going out of business. As of yesterday, everything in the store was 25% off list price. Since Radio Shack is a little more expensive than industry suppliers, that may not be compelling, but the discounts will increase. I'm wondering if I want even more Arduino hardware (which I hope one day to get around to using!).

Speaking of long-awaited projects, let the record show that I have finally started building the bookshelves needed to hold at least some of the books that I brought home from my UGA office.


The comet is still there

Comet Lovejoy is actually quite clearly visible in binoculars, but the full moon near it in the sky makes it unduly hard to see and photograph well, and keeps us from seeing the tail. This is a cropped portion of a single 15-second exposure with a Canon 60Da at ISO 1600, Sigma 105/2.8 lens at f/5, iOptron SkyTracker. The star at the left is 46 Eridani.

M42 with an old "cat"

Just to see what would happen, I got out my 1986-vintage Spiratone Minitel-S 300-mm "cat" (catadioptric, mirror) telephoto lens, which I bought for $99 in their Manhattan showroom Back in the Day. (See also this.)

What you see above is a stack of three 15-second exposures in the light of the full moon, with a Canon 60Da, ISO 1600, on an iOptron SkyTracker.

Back in 1986, I tried this lens for astrophotography, found it sharp compared to the comparably priced all-glass lenses of the time, and wrote a favorable review of it for Astronomy. I also sent a picture taken with it (of M8 and M21, I think) to Spiratone and they exhibited it in their showroom. That's one way to make it into a New York gallery...

The lens was also getting good reviews from terrestrial photographers, including Herbert Keppler.

But then I stopped using it for astrophotography because of its tendency to produce double-doughnut, figure-8-shaped reflections around bright stars. (You can see one faintly below the center of the picture.)

Now it's 2015. The first thing I noticed when I focused the Canon 60Da is that the star images were not critically sharp and looked a bit out of collimation. (My Canon 300-mm lens resolves the Trapezium when I'm focusing; this lens doesn't.) In fact, my star images were about 8 pixels (= 40 microns = 25 arc-seconds) in diameter. If I wanted them round I'd have to go slightly out of focus and make them even bigger.

In the film era, that was acceptable. Film star images were commonly 50 microns or larger. In those days, we didn't worry nearly so much about guiding accuracy.

Today, cameras need better lenses and have them. With either of my good telephoto lenses (Sigma 105/2.8 or Canon 300/4 non-IS), the star images are about 2 pixels (= 10 microns = 6 arc-seconds with the 300-mm lens) or even smaller. I actually pick up more detail if I use the 105/2.8 lens (and enlarge the image) than if I use the Spiratone 300-mm "cat." I may end up using the Spiratone as a guidescope.

The only "cat" lenses whose reputation has survived the test of time (apart from astronomical instruments) are the Vivitar Series/1 "solid cats" designed by Perkin-Elmer. I sometimes wonder how well such a lens would perform on the stars — but I wonder if internal reflections would be a problem.

That trip to New York in 1986, for my first meeting of the Association for Computational Linguistics, was great fun. Although I had been in Manhattan quite a few times in the immediately preceding years, this was a last chance to see a lot of classic mid-century photography stores before they started drying up. Besides Spiratone, I visited Cambridge Camera Exchange, Seymour's Exakta (which was a telephone inside Cambridge Camera Exchange), Willoughby's (a thriving superstore), and Olden (which seemed half fossilized already, with some areas roped off; the most interesting thing I saw there was an old Reflex-Korelle large-format SLR). I was outfitting a darkroom at the time and bought my good enlarging lens (Schneider Componon-S 50mm) and my digital enlarging timer on that trip, both, I think, at Willoughby's.


Here come the under-$200 PCs

I didn't realize this until a friend prodded me to look, but you can buy a brand-new single-core Windows PC for less than $200. I'm not talking about refurbs or last year's model.

So if you don't really need any more computer power today than you did 5 years ago, but you do need a new machine, take heart — prices have come way down.

Here, for instance, is an 11-inch Hewlett-Packard laptop with Windows. Single-core CPU, 2 GB RAM. There's only 32 GB of hard disk — but wait a minute — that disk is a solid-state drive, blazing fast and easy on the battery.

And the HP Pavilion Mini Desktop, list price $179, packs a similar amount of computer power into a little box (like a Mac Mini) to which you attach your own keyboard and screen.

These are fine for e-mail, Web surfing, and office work, including serious spreadsheets, word processing, statistics, and photo and audio editing. (My main laptop for several recent years was comparable to these, and it worked fine.) They're probably not sufficient for World of Warcraft or for video editing or some types of software development.

At that price and size, I'm expecting the Pavilion Mini also to show up in kiosks and automated machinery. Not too long ago, an "embedded PC" for machine control cost about $150. Maybe it still does.


Rigel and the Witch Head Nebula

Here is the last of my astrophotos from the December 13 trip to Deerlick. This is the star Rigel in Orion and, over on the right, a large but dim reflection nebula called the Witch Head (IC 2118). Stack of seven 1-minute exposures, Canon 60Da at ISO 3200, Sigma 105/2.8 lens, iOptron SkyTracker, corrected as usual with dark frames and flat fields.

A group of friends gathered this evening (January 3) at Manuel's Tavern in Atlanta to remember and commemorate Tim Nix. We are sad at his unexpected passing, and all the more sad because this apparently leaves the southeastern United States without a telescope dealer! The nearest substantial ones are apparently in Texas and Maryland. Tim's store, Camera Bug, was not just a supplier for us; it was an information hub and gathering place. It, and he, will be missed.

The holidays are over, I have plenty of real work, and the Daily Notebook will be quieter in the coming days. But I'm not going away...


More UFOs explained

The CIA has revealed that a large number of UFO sightings in the 1950s and 1960s were actually flights of the secret U-2 high-altitude spy plane.

Reportedly, this accounts for "more than half" of the reported UFO sightings of the period. They mean the sightings reported by aviators and characterized as aircraft-like objects flying at seemingly impossible altitudes.

We already learned, a few years ago, that other UFO sightings were secret high-altitude balloons.

And then there are the rest. When a UFO "flap" is going on, people with vivid imaginations but no experience looking at the sky will look at bright stars, clouds, or other ordinary sights and claim to see spacecraft being piloted by bug-eyed monsters. Several times recently I've dealt with UFO reports that were just jet contrails seen in the sunset. More about this here.

In my early days as an amateur astronomer, I read a book about Project Blue Book, the Air Force's project to collect UFO reports. (I think it was Ruppelt's 1956 book.) I didn't expect UFOs to be alien spacecraft; I thought UFOlogy would reveal interesting things about rare atmospheric and astronomical phenomena and optical illusions. Clearly, I was a nonbeliever, and not the kind of person the rest of the then-abundant UFO books were written for.


I've photographed the Pleiades many times before; here's another. This is a star cluster in the constellation Taurus that includes some dust clouds that reflect light. Their name in Japanese is Subaru and is the name of a car company whose logo depicts this star cluster.

Stack of five 1-minute exposures, Canon 60Da with 105/2.8 lens, on an iOptron SkyTracker at Deerlick.


My new year's resolution is 1600×2560...

On the last day of 2014, I stopped in at the local Best Buy and scored a 45% discount on an open-box Samsung Galaxy Tab S, 10.5-inch, 32 GB (which seems to be a Best Buy exclusive, but the price I got would have been a bargain even for the more common 16 GB edition).

This was a long-planned purchase, and the last step in the planning was when Apple scared me away from the iPad world a few days ago. Additional reasons for preferring the Samsung are the Android operating system (for which I can write my own programs) and the larger screen.

I plan to use it mainly as an e-reader for PDF files. The University Libraries give us free downloads of all Springer mathematics and science books, in PDF, and that is also the format in which most scientific journal articles reach me. But these are images of printed pages — not reflowable like Kindle or Nook books — so I need a screen big enough to view them properly.

I have been viewing them on PCs, but it's annoying having to view a vertical-format page on a horizontal-format screen.

I'm solidly in favor of what Apple calls a Retina display and Samsung also offers, namely a very high-resolution display (about 300 pixels to the inch). I can remember when computer monitors had "0.4 mm dot pitch," meaning about 60 dots to the inch, but those dots were not pixels. They were the individual red, green, and blue spots on an old-style color CRT. To work properly, each pixel had to be blurred to about 1/20 inch in diameter, which caused constant eyestrain because the image was always blurry. A more recent standard is about 125 to 150 pixels to the inch — that's how sharp most PC screens are nowadays — and it seems to be satisfactory. But for prolonged reading of material intended to be printed on paper, I want as much resolution as possible, more resolution than the eye can see, so that the limiting factor is no longer the screen but rather the eye. That's what Apple calls a Retina display, using that trademark for various displays that are about 200 to 400 pixels per inch.

Samsung uses an AMOLED display in which the pixels actually emit light of great spectral purity (they are LEDs). That makes possible higher contrast and better color saturation than traditional backlit LCD displays, in which the pixels are electrically activated filters in front of a white backlight. In principle, if done right, AMOLED technology should be able to produce any color the human eye can see, because LEDs can be made nearly monochromatic at any wavelength. I wouldn't call it perfect yet, but it's certainly brilliant and readable.

One stumblingblock in the path to higher-resolution displays is the fact that Windows software traditionally counts the pixels — the size of objects on the screen is measured in pixels. We went through several generations of laptops where every time a new kind of screen came out, the software shrank until you couldn't read it! The new WPF API specifies sizes in distance units, not pixels, and software written the old way is simply scaled up to occupy more pixels than it thinks it's getting.

Comet Lovejoy again

On the evening of the 31st, in bright moonlight and under a somewhat hazy sky, I photographed Comet Lovejoy C/2014 Q2 passing through Lepus. Here are two presentations of the same picture. Six 30-second exposures with a Canon 60Da and 300-mm lens at f/5 were stacked using DeepSkyStacker, which separated the comet from the stars, stacked them separately, and then recombined them.

The second picture is a high-contrast black-and-white rendering, with plenty of noise (causing a mottled background), but the tail of the comet is faintly visible.

Colorful moon

Colors adjusted Jan. 5

This is the more-than-half-full moon that was in the sky not far enough from the comet. I took this picture to refine some techniques; the air was unsteady and it is not as sharp as it could be. Six 1/320-second exposures were taken at the Cassegrain focus of my old Celestron 5. The raw files were converted to quarter-size (superpixel-mode) TIFFs using PixInsight (which produced low-contrast images with a greenish cast), then stacked with AutoStakkert 2, then sharpened with RegiStax, then color-corrected with Photoshop. In the last step, color saturation was increased to bring out differences between different kinds of rocks on the lunar surface.

Useful word of the day: preternatural

Most of us have heard the word preternatural but don't know exactly what it means, except that it's somewhat spooky.

It turns out that in late medieval philosophy, this word had a precise meaning, and it's an old way of describing what has become a familiar concept.

In scholastic philosophy, God has supernatural power — He is completely above the laws of nature and can alter them at will. Preternatural power is something less; it is the ability to use laws of nature in ways unknown or unavailable to us, but nonetheless still subject to law. Angels and demons have preternatural, not supernatural, powers.

That is a very familiar concept today. It is exactly what Arthur C. Clarke had in mind when he said, "Any sufficiently advanced technology is indistinguishable from magic." Much science fiction revolves around utilizing the laws of nature in ways unknown to, and not understood by, others. As another example, Superman's super-powers are preternatural; they are law-governed; in fact, most of his story plots involve bumping into their limits.

Later on (after 1600), early scientists used the word "preternatural" to denote things that are natural but rare and poorly understood, such as rare deformed animals. But that was not its original meaning.

Now you know.

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