Michael A. Covington    Michael A. Covington, Ph.D.
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How many lights, darks, and flats?
LED vs. CFL vs. incandescent bulbs
What not to do — Facebook fails ethics
Solar eclipse
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Museum day


Melody's and my first date was a visit to the Georgia Museum of Art exactly 48 years ago today. So we went to the museum today, as we plan to do regularly every April 28.

We looked at some familiar items from the permanent collection. The painting behind us in the picture is Bridge at Old Lyme, by Frederick Childe Hassam, 1908 (better image here but the link may not be permanent).

We passed up an exhibit on the horrors of Hiroshima (complete with noises) and a display of some coffin-like steel plates representing death, and glanced only briefly at some large images of Milton Berle's filing cabinets, but we enjoyed a display of abstract art by Nancy Baker Cahill (see also this link, as long as it lasts). Her art starts as graphite pencil drawings, then gets digitized, turned into three-dimensional sculptures and animations, and often eventually turned back into still pictures that are very colorful.


What not to do — Facebook fails basic ethics

(Also posted on LinkedIn.)

Something happened to me this evening that belongs in the computer ethics textbooks.

There is a big ethical difference between saying "You have triggered an alarm" and "You have done wrong." People also have a duty not to claim that the results of a computation are more accurate than they are.

This evening Facebook broke both of these rules and kicked me off temporarily. Their bot told me I had violated their community standards but didn't say why. They pointed me toward a vague rule against scams and impersonation.

Their exact words to me were, "Your Facebook account has been suspended. This is because your account, or activity on it, doesn't follow our Community Standards on account integrity or authenticity."

They did not indicate what standard they thought I had violated, nor what activity was supposed to constitute the infraction.

I had been trying to warn my friends about a piece of malware that is circulating on Facebook, and to tell them to turn on Tagging Review to keep it from spreading on their page.

I quoted a few words from the scam posting itself -- and that was apparently enough to get me kicked off Facebook. I also linked to a page in the Facebook help system, and it seems they also object to that.

Fortunately I was able to appeal the ruling, submit proof of identity, and get reinstated within half an hour or so. But then I tried to post about the same thing again — not quoting its words this time — and my posting was again deleted as violating community standards! Fortunately I wasn't kicked off.

Apparently the objectionable thing in the second posting was simply that it linked to a Facebook help page. I was trying to be helpful. The bot must have thought I was impersonating Facebook management.

Now... I understand the need to take immediate protective action when something appears to be dangerous. But that is not the same as accusing a human being of wrongdoing and punishing him without due process. Sysadmins in the 1990s sometimes wanted to be judge, jury, and executioner, and at UGA we had to caution them that that is not their job. It looks like Facebook has not yet grasped this.

A moonscape


Last night's astronomy session was mostly for calibrating the PEC on my Losmandy mount, but at the end, I couldn't resist taking an image of the nearly full moon. This was done with an AT65EDQ apo refractor (6.5-cm f/6.5) and an ASI120MM-S monochrome camera, both of which were on the telescope for testing tracking, but were also suitable for taking this picture. This is an enhanced stack of the best 50% of about 6,000 video frames.

At the top center is the great crater Copernicus; at bottom right, Tycho, with its rays; and at left, the dark crater Grimaldi. If you go straight down (vertically in the picture) from Grimaldi to the edge, you're in the neighborhood of Mare Orientale.


Do you need an electrician and not know it?


Further to what I wrote yesterday... Last week we finally got around to having the electricians in, catching up with a list of small jobs that we had been accumulating for years. And I realized — We should do this more often. Most people simply never have electricians come in unless something is broken. But lots of minor improvements and modernizations need doing all the time and are surprisingly affordable.

We've used Blue Moon Electric (Athens, Ga.) for several jobs recently. They are reliable and cost-effective. Remember to compare quality when comparing prices.

I'm a rather capable do-it-yourselfer, having been familiar with electrical work since childhood, but I'd rather pay professionals for anything elaborate. I'm not good at climbing. I don't know the tricks for fishing wires through walls or concealing openings in sheetrock. I don't know the nuances of safety requirements for running wires in unusual places. So for anything that isn't really easy and out in the open, I prefer to pay a professional.

(If you do any electrical work yourself, the vitally important thing is to follow standard practices and not improvise. It's not just whether something works, it's whether it's safe under unforeseen conditions. Electrical codes are based on detailed research about what can go wrong, even in fires and floods. If you don't know the standard practices, call on someone who does.)

Here are some reasons you might want to have an electrician come in:

  • More overhead lighting? Besides adding or changing conventional light fixtures, you could add LED downlights, a new development, which are surprisingly easy and inexpensive to install and fit almost anywhere.
  • More outlets? Anywhere you've been using an extension cord for a long time is worth looking at. It's surprisingly easy to add more outlets along a wall. There can even be outlets in floors. And Leviton makes a handy gadget that replaces an existing double outlet with a quadruple one with no new wiring.

    (Side issue: When you add outlets, are you overloading your circuit? A licensed electrician will do the calculations and make sure you're not. But here's an encouraging fact: Modern technology has been reducing the load on our circuits for years. Lights take 1/5 as much electricity as in the 1960s, and TVs and stereos take about 1/10 as much, or less. Air conditioners take less than half as much. High-power appliances such as vacuum cleaners, space heaters, and toasters are still heavy loads, but modern electronic devices are not; the total load has gone down dramatically.)
  • Worn switches or outlets? If an outlet won't grip the plug, or a switch seems loose or fails to toggle firmly, then it needs replacing.
  • More safety? Outlets near water, in bathrooms, kitchens, and outdoors, need GFCIs (ground-fault circuit interrupters) to protect people against electric shock. This is a simple replacement.
  • Worn circuit breakers? If you have a circuit breaker that trips regularly (I would define "regularly" as more than once in five years!), then either the circuit is overloaded or the breaker itself has deteriorated. Someone needs to figure out which. Newer breakers can have GFCIs and arc-fault detectors built in for extra safety.
  • Need three-prong outlets? Outlets in older houses only accept two-prong plugs. There are improvised adapters for putting three-prong plugs into them — with loss of safety! — but there's also an easy, correct solution that is fully safe but doesn't require pulling three-wire cables. A GFCI powered from a 2-wire cable can be completely safe with a 3-prong plug plugged into it. It doesn't actually connect to ground, but it does detect current that would flow to ground when contact is made accidentally, and shuts off power to protect you.
  • Signs of trouble? If lights dim more than slightly when you turn on a high-power appliance, or if they flicker and it's not attributable to LED problems, then there may be something seriously wrong with your wiring, and it should be checked promptly.

    Even worse, if lights brighten when you turn on an appliance, you have an emergency! It's called an open or high-resistance neutral, and it's dangerous. What it means is that part of the power to some of your circuits is flowing through other circuits, varying the voltage available to them. If the deterioration continues, some of your 120-volt appliances may get 240 volts across them, causing damage or fire.

Those are just a few things that come to mind. Most of us ought to give more thought to maintaining and improving the wiring in our houses. After all, we maintain and even improve our cars regularly; why not our homes?


Twilight of the bulbs

We had some electrical work done this week in several places in the house, and that led me to go around and look at other electrical things, and to clean out the cabinet where we keep light bulbs and extension cords.

We have too many extension cords, so any with visible wear, even if slight, were thrown away.

We also had too many light bulbs, and I decided not to keep any compact fluorescent (CFL) bulbs. They are a technology whose time has come and gone. LED bulbs are slightly more efficient and a great deal longer-lasting. Some CFLs are still in use, of course, but they will be replaced with LEDs when they wear out, or sooner. Even if in working order, the spare CFLs were discarded because they will never be used; an LED bulb will always be better.

Compact fluorescent light bulbs

I decided to keep all our incandescent bulbs because regulations have made them expensive or unobtainable, so if I need one it will be hard to get, and because if I gave them to someone to use indiscriminately, I would be burdening them with a hidden cost — they take 5 times as much electricity as either of the other two kinds. But there is one situation in which incandescents are ideal: a harsh-temperature environment (such as an attic) where the bulb is seldom turned on.

Incandescent light bulb

Both LED and CFL bulbs contain voltage-converting circuitry that deteriorates in hot, and maybe in cold, environments. Not incandescents. They are designed to run hot and to survive heating up and cooling down many, many times. In places where the bulb is rarely used, but needs to be ready when needed, even after not being used for years, they are the choice.

Good idea: Flat LED downlights (canless wafer lights). We had a couple of these installed in the ceiling of Sharon's bathroom. They are cheap and easy to install. My electrician and I recommend the Juno product line, which is much less flicker-prone than some earlier, cheaper ones we had installed a couple of years ago. The installation does not require a box, and even running into a joist won't normally block an installation because the fixtures are as thin as the Sheetrock; see for example this video.

A canless wafer light (LED downlight)

Why LED lights sometimes flicker: I've been reading up on it, and one of my suspicions is confirmed. If an LED bulb or fixture flickers occasionally, but others substituted for it do not, and nothing else flickers in unison with it, then the problem is not in the wiring. It is the bulb or fixture itself and is caused by substandard electrolytic capacitors in the LED driver circuit, which is inside the fixture or bulb. If you do your own circuit-board repairs, here and here are videos about replacing these capacitors. I'm going to attempt one soon. I recommend Panasonic's high-temperature line of electrolytics.

Electrolytic capacitors deteriorate with temperature and age, especially when not being used. A substandard one will often improve with steady use, because the insulating coating inside of it actually improves (through an electrochemical process) when there is voltage on it. More about electrolytic capacitor reliability here.

More thoughts about light bulbs: Back in the good old days, all light bulbs of the same wattage and same overall type were alike, even if different brands; you could mix them freely. Then, as CFL and then LED lighting took over, it was hard to ever get the same bulb twice — even the same brand of bulb would be different when you bought another one six months later. This made matched sets almost impossible to obtain and left us with lots of awkward mismatches. Nowadays, thank goodness, things are stabilizing. You have to match bulbs by overall shape, brightness, and color temperature (such as 2700 K), but different brands look much more alike.

I have no enthusiasm for the technological fidgeting that has led to bulbs that change color and are controlled by Bluetooth or something. But I suppose someone has a use for them.


After the eclipse

Cloudy: The distinctive thing about this solar eclipse, in contrast to 2017, is that most of the path had cloudy weather — high, thin clouds if nothing else — meaning pictures don't show the faint outer corona. The weather changed at the last minute, and many of the best eclipse photographers were completely or nearly clouded out. The best views were had by people who thought they were going to second-rate sites, such as my grandchildren in Scottsburg, Indiana (with only one minute of totality).

Fake pictures: The lack of good pictures created a vacuum in which some people were able to share fakes. Unlike last time, I haven't seen obvious fakes with the sun in front of clouds, or anything like that. But a famous painting by Cathryn Machin, based on a spectacular high-dynamic-range photograph by Sebastian Voltmer, is being circulated on Facebook as if by "NASA's James Webb Space Telescope." (The James Webb Telescope is far too far from the earth to see a solar eclipse, and it would be destroyed if it were aimed anywhere near the sun.) Apparently to elude image-search engines, the fake that I saw had been mirror-imaged and rotated.

Update: The fake pictures have started. Many are dead giveaways, such as eclipse in front of clouds, or eclipse with scenery not in the eclipse path (e.g., the Seattle Space Needle). Don't be taken in.

Eye injuries: Because I write about eclipses, I keep track of eye injuries caused by improper viewing (see also here) in the hope of fine-tuning the warnings given to the public. So far I have not heard of a 2024 eclipse eye injury (if you know of one, with confirmation, not just gossip, please tell me). But there is already a hoax circulating about how a boy was blinded — actually a video "skit" from 2017.

There is also an optometrist somewhere saying "viewing the eclipse is not worth the risk," which is not the usual recommendation. You might as well tell people not to go to the Grand Canyon because of the risk of falling in. For recommendations by an optometrist whose specialty is eclipse safety, click here. Eclipse glasses and pinhole projectors are safe and injuries have become rare. They happen by deliberate defiance, not by accident.

[Update:] There are starting to be scattered reports, all about people who viewed the eclipse with no protection at all, or in one case "through a phone" whatever that means. It will be some time before we find out whether the injuries were severe. There are also reports of eclipse glasses that did not meet safety standards, but no injuries are attributed to them, and it's not clear how far out of spec they were; if they had even half the specified density (log scale) they would probably prevent injuries but be difficult to use. I await more information.

[Update:] I have heard of one politician "blaming the eclipse on climate change," which makes me wonder what someone thinks an eclipse is. I wonder if this is a garbled report of someone blaming the inaccurate weather forecasts on climate change, which is plausible.

Besieged: Naturally, I posted about the eclipse on Facebook, and I can't keep up with the number of people wanting to communicate with me about it. It's nice to hear from everybody all at once, but I'm not on Facebook full-time and can't commit to even seeing, much less answering, everything that is sent to me. It has been wild!

No more for a long time: The sad thing about this eclipse for me is that it is the last one for a long time. In the eastern United States, we have to wait until 2045 for a total eclipse (at which time I will be almost 88 years old) and 2029 for even a good look at a partial one (there are partial eclipses less conveniently observable in 2026 and 2028).

That means this year was probably the last time I will have been involved in educating the American public about an eclipse — something I first did as a middle-schooler in 1970.

The other side of the world doesn't have such slim pickings. If I can get away and fund the trip, I would be glad to go to Spain in 2026, Gibraltar in 2027, or Australia in 2028. Maybe...


Solar eclipse

Today, a surprisingly large part of the U.S. population was in the path of a total solar eclipse, which passed over Dallas, Little Rock, Indianapolis, Cleveland, Buffalo, and Rochester, and then grazed Toronto and Montreal.

Unfortunately, I was not able to travel to see it. Many who did so were disappointed, because unpredictable weather took its toll, and many sites were unexpectedly cloudy.

My grandchildren and their parents, however, had an excellent view of the eclipse from Scottsburg, Indiana. At least I helped make their trip possible, even though I could not be there with them.

Here in Athens, Georgia, we had a deep partial eclipse. This picture is a stack of 12 exposures, aligned and sharpened.


Here's the equipment I used — a vintage-1980 Celestron 5 with a vintage-2012 Canon 60Da camera and a relatively new Thousand Oaks solar filter.


I also did a lot of amusing experiments with crescent-shaped spots of light. You have probably noticed that when sunlight goes through a small hole in a wall, the resulting spot of light is larger than the hole, and is round. It is in fact an image of the sun. During an eclipse, those spots are images of the eclipsed sun, which is crescent-shaped.

So here I am, making a small hole with my thumb and forefinger, and letting the eclipsed sun shine through it. You'll see that the same thing also happened accidentally with my collar, making a second, less distinct, crescent-shaped spot of light.


Here are crescents of light in the shadow of a tree:


And for the pièce de résistance, here's a colander and its shadow:



I first noticed this phenomenon when observing an eclipse with my father and sister in 1963 at our house in Moultrie. Dad drilled holes of different sizes in a scrap of countertop and found that they all worked; the smaller ones worked better. I also noticed a similar, though less distinct, effect with light coming through the wall of the carport, which had bricks spaced apart (see this picture).


How many calibration frames (darks and flats)?

Stand by for further coverage of this later, but here are some preliminary results.

With the help of some other astrophotography experts on the Cloudy Nights forum, I've been doing mathematical analysis of the way deep-sky images are calibrated and stacked. We normally take many exposures of the object ("lights"), matching dark frames to counteract fixed-pattern noise in the sensor ("darks"), images of a flat field to counteract pixel non-uniformity and dust specks ("flats"), and "flat dark" or "bias" frames to subtract out the nonzero baseline in the flats.

How many of each should we take? Preliminary results:

Lights: As many as possible. My current practice is to take 20 to 120 2-minute exposures. The biggest source of noise in the finished image is shot noise (Poisson noise) in the lights, and if you take N lights instead of one, you have 1/sqrt(N) as much of this noise.

Darks: Need not be as numerous as the lights, because they do not have shot noise from the image, although they still have read noise. Their purpose is to correct hot pixels and fixed-pattern leakage. Some of the newest sensors may not need them. My practice will be to take 10 to 20.

Flats: Need not be numerous because any noise in them is small compared to the signal. Expose them as generously as you can without actually bumping into the sensor's maximum value, so that their read noise will be as small a fraction as possible of the total output. Generous exposure helps more than taking a lot of flats. My practice is to take 10, which may be more than are needed, but they're quick to take.

Flat darks or bias frames: A few are sufficient; I currently take 10.

The big discovery is that dithering is VERY important. Dithering means not aiming the camera at exactly the same point in the sky for all the exposures. That way, when frames are combined, lined up on the stars, any noise that is in fixed positions on the frame will be spread around and averaged out.

And where does this noise come from? Residual random noise in the master dark and master flat. Each of those has a small amount of read noise that couldn't be eliminated, and it's in a fixed position because the same master dark and flat are applied to all frames. So the frames need to be dithered on the stars, to spread this residual noise around. The benefit can be dramatic.

Even a little dithering helps a lot. It can be sufficient to spread the whole session across just four or five positions. So when I'm using a star tracker that can't dither under computer control, I'm going to simply stop it and re-aim it periodically, shifting randomly a small fraction of the field of view.

Some time back, Robin Glover demonstrated that if the exposures are reasonably generous (so that the sky background is appreciably lighter than black), the read noise (random noise) in the sensor is surprisingly unimportant; we can put the brakes on our headlong rush toward lower-noise sensors, although I still want one because they tend to be better in other ways too. That conclusion holds up through all my analyses.

Note however that his recommended exposures pertain to faint objects and assume that, in the finished picture, the sky background will be medium-dark gray. It is quite legitimate to use shorter exposures if you are photographing a relatively bright object (such as M42) and are going to render the sky darker.

News updates

Sadly, for several reasons, we're not going to get to go to Indiana to see Monday's solar eclipse, as we had planned. I will observe it from here, where it will be a deep partial eclipse, and hope that the grandchildren have a good trip to totality, which passes near their home.

Not only is Melody not quite up to a long road trip yet, yesterday I had some urgent dental work done. I was sent to Tucker, Georgia (Melody's childhood home town) when the dental surgeon in Athens suddenly had to cancel. So I was right across the street from where she went to 8th grade, and down the street from where she went to church, and even got to see (momentarily) the public library. And today I'm eating applesauce for breakfast. Hoping to be back to normal soon, but glad not to be driving to Indiana today.

Meanwhile, the State of Georgia has stopped publishing the blue COVID graphs that I've quoted so often. I'd say, "The war is over," except that I had COVID just two months ago.

"Thou shalt not bear false witness against thy neighbor"
Another aspect of weaponized stupidity

I am finding that many of my fellow Christians are very poorly instructed about this one of the Ten Commandments. In fact, they often feel they are doing very righteous things when they violate it.

The commandment says not to make false accusations. I take that to include not spreading accusations of wrongdoing without good evidence and a good reason to spread them.

Even when the one accused is an organization, or a person known to have other serious faults.

If you're saying someone did wrong, this commandment applies to you.

I know that sometimes, someone else's wrongdoing is a matter of public concern. If so, I think you still have a duty to be honest about the evidence, about whether the wrong is proven or just suspected.

"I heard" or "somebody said" is not good enough. Nor is "my best friend shared this on Facebook" where "this" is something from a perfect stranger.

I have had to rebuke some of my fellow Christians rather strongly for spreading the hoax that "Facebook has banned the Lord's Prayer." Facebook has not done that, and if you check, you'll find no evidence that it has. There is no controversy. Just gossip.

But people spread it the moment they hear it from a total stranger. And they feel so righteous when they spread this malicious lie!

Maybe because they're blaming an organization rather than an individual; maybe because they think they're supposed to hate secular organizations, even when relying on them; or maybe because they're just foolish.

There's a deeper layer here. What I am realizing is that some people don't even know what truth is.

I take it for granted that truth is facts; truth exists in the real world; truth is what you can confirm by looking at the real world.

For some, though, truth is just words running around in your head, things you're supposed to say.

For some, truth is just emotions. If you "feel" like believing or saying something, you believe it and say it. To such people, logic and evidence don't matter. It is sad, but such people are surprisingly numerous.

And for some, truth is a matter of taking sides, like choosing to cheer for the Gators or the Bulldogs; and then you're supposed to say what your side says, or what seems to show loyalty to your side.

I think that with the Lord's Prayer Hoax we're seeing the last of these. People think that to be loyal Christians, they are supposed to believe and spread any accusation of anybody persecuting Christians, whether or not it is true.

If the Book of Proverbs is still in your Bible — if you have any idea what godly character is — this isn't it.


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