"Rare super blue blood moon eclipse" — what?!

The media are all agog about the "rare super blue blood moon eclipse" about to happen on Wednesday morning. What's really going on?

Quick answer: We have an eclipse of the moon, only partly visible from the eastern U.S. The West and Asia will get a better view.

It starts at 6:48 a.m. EST on January 31, which, as seen from Georgia, is just before the moon sets; we don't get to see the moon completely eclipsed. No eye protection is needed since this is the moon, not the sun. For more information click here.

Is there anything unusual about it?

Well... blood moon is what some religious cultists have started calling all eclipses of the moon. The moon typically looks reddish when eclipsed, due to light reaching it edgewise through the earth's atmosphere. There is a lot of nonsense about "blood moons," circulating among a sect of Christians who picked up some kind of "prophecy" that is not in the Bible.

OK then, super. "Supermoon" means the moon is near its minimum distance from earth. It reaches minimum some time every month, and sometimes that coincides with full moon; sometimes it even coincides with an eclipse. Depending on how narrowly you define supermoon, a few percent of lunar eclipses occur at supermoon; they're not excessively rare, and they don't have any astrophysical importance.

We had an eclipse during "supermoon" in 2015. Picture and more explanation here; still more details here.

Finally, blue. Some decades ago, Sky and Telescope Magazine was asked what the phrase "blue moon" meant in old almanacs, and the answer they gave might not be correct, but it stuck: A blue moon is the second Full Moon in a single calendar month. Since most months are longer than the moon's orbital period, this happens occasionally. As it happens, this month (January) has two Full Moons, February has none (it's the only month shorter than the moon's phase cycle), and March again has two. That's an interesting coincidence, but it's not really something to see. It's just an artifact of our clumsy calendar.

One more thing. Due to a well-known optical illusion, the moon looks bigger when it's near the horizon, rising or setting. It also looks bigger when you're paying more attention to it. This is the main thing people are noticing when they remark about how big the moon looks. Near the horizon, it is easier to keep your eyes focused on the moon, so you see more detail in it, and you have trees and buildings to compare it to. It impresses people more than the moon high up in a blank sky.

So should you go out and see it? It's interesting to look at the moon at any time. Don't wait for the media to hype something; go out and enjoy the sky! But take note of the fact that media coverage has gotten out of hand. They are now reporting every little set of coincidences as "rare."

Almost all my writing time is being spent on Digital SLR Astrophotography, not on the Daily Notebook. I'll see you in February!

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Short notes

A government shutdown is like quarrelling parents neglecting to feed their children.

Congress has a job, and they're not doing it. We need a mechanism to prevent shutdowns. Department-by-department budgeting might help, or maybe we need a constitutional amendment to automatically renew the previous budget if a new one is not passed — and maybe trigger an election for all of Congress!

On the occasion of the March for Life, I want to point out that there is no necessary connection between opposition to abortion and right-wing politics. It could easily have gone the other way — one might expect capitalists to assert a woman's total ownership of her body and socialists to want to protect the unrepresented, non-property-owning fetus. For more on the abortion controversy click here and here.

I am devoting almost all my writing time to revising Digital SLR Astrophotography. That's the only reason not much is appearing in the Daily Notebook. Things are going smoothly here and I'm getting a lot done.

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A point on which probability theory is misleading

I'm reading Jordan Ellenberg's How Not To Be Wrong, a book whose theme is, "mathematics is the continuation of common sense by other means."

Ellenberg explains, entertainingly, to the nonspecialist, some mathematical concepts most of which I've already been using daily for a long time.

And I want to share an adaptation of one of his examples — a point on which classical (frequentist) probability theory is misleading.

Suppose you're playing with dice, and you roll one of them four times, and it comes up 2, 4, 3, and 6, in that order. Then you roll the other one, and it comes up 2, 2, 2, and 2.

Your gut feeling is that the second die has done something unlikely.

But classical probability theory says that 2, 4, 3, 6 is just as unlikely as 2, 2, 2, 2. A die can give you any number from 1 to 6 any time it wants. It has no way of knowing whether it's repeating itself.

And on this point, classical probability theory is misleading.

The reason? Classical probability theory doesn't take prior knowledge into account.

The reason 2, 2, 2, 2 strikes you as fishy is that you know that it's relatively easy to rig a die to roll the same number over and over, and cheaters actually do this. It's almost impossible to rig a die to roll 2, 4, 3, 6, and we've never heard of anybody doing it.

So the reason 2, 2, 2, 2 strikes you as unlikely is that it supports a hypothesis that is unlikely but worth noticing. Your prior knowledge tells you that 2, 4, 3, 6 does not suggest anything fishy, but 2, 2, 2, 2 does.

A big problem with classical probability and statistics is that they don't tell you how to change your knowledge. Classically, every experiment and observation exists in total isolation. I've written about this before.

Another problem with statistics as practiced today is that too many foot-soldiers of science have been miseducated into believing that a p value below .05 confirms a hypothesis. Science becomes a search for p<.05, which dooms it to being wrong about 1/20 of the time!

Some dogmatists even maintain that you must not care about the value of p except whether it is above or below .05. You have to "choose" .05 as the cutoff point before even doing the experiment.

That is balderdash. A p value of .001 really does tell you something that a p value of .05 does not. If you blind yourself to that fact, you're ignoring scientific evidence.

In fact, as Ellenberg emphasizes, the original advocate of p values, R. A. Fisher, never said that p<.05 confirms a hypothesis! He said it indicates a hypothesis worth pursuing. Confirmation comes when repeated experiments regularly and reproducibly produce low p values.

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Meltdown and Spectre, or what's wrong with those Pentiums

There have been some very confusing news reports today that something is wrong with almost all Pentium CPUs as well as lots of others, and to fix it, they're going to have to be slowed down. The flaws have been given the scary names Meltdown and Spectre.

I don't have full technical details myself, but I want to explain, in layman's terms, what I know.

What has happened?

A new way has been found for viruses and spyware to do their mischief. Specifically, a new way has been found for running programs to spy on other running programs. It is quite different from anything viruses or spyware have been able to do until now, so new protections are needed.

Is it dangerous to use my computer?

No. All that has happened is a new opportunity for viruses and spyware. Ordinary software is not affected.

In fact, there are no reports of viruses or spyware actually using the newly discovered vulnerabilities yet.

How can I protect my computer?

If you have third-party antivirus software, update it with today's update. Then get today's Windows update or MacOS update, and stay tuned for more updates coming in the near future.

I heard it would slow my computer down 30%. Will it?

So far, today's Windows patch slowed my computer down just 3%, judging by the measured speed of an image-processing application (PixInsight). I expect the slowdown to decrease as the later patches become more sophisticated.

Will my computer melt down?

No. The names Meltdown and Spectre are needlessly scary.

OK then. What exactly has been discovered?

It has to do with speculative execution, which is a way modern CPUs do their work faster. Basically, CPU manufacturers have been speeding things up in a way that wasn't as safe as everyone thought.

Here's how it works. Computer programs constantly have to make decisions, such as, "If this amount is a deposit, add it; if it's a withdrawal, subtract it." Modern CPUs can do more than one thing at a time, so in that example, if the adder and subtracter aren't already busy, the CPU will both add and subtract the amount while finding out whether it's a deposit or withdrawal. Then both numbers will be ready, and it will take the one that's needed and throw away the other. That's faster than waiting for the decision before doing the addition or subtraction.

Large parts of all computer programs work this way, and here's the problem: Ways have been found for a running program to get information about what was on the road not taken, even information belonging to a different running program.

And that has to be stopped, because it gives viruses and spyware a new way to spy.

In the short term, operating system kernels are being rewritten so that programs don't get that close to each other. That's where the slowdown comes from. Nothing important and confidential can be left within reach of this newly discovered spying technique.

In the long run, the CPUs themselves are going to be redesigned to eliminate the indirect ways in which spying turned out to be possible.

Is this Intel's fault?

Intel is actually not the only manufacturer whose CPUs are vulnerable, although their Pentium family (including Core, etc.) is the worst off. Speculative execution is an industry-wide technique, and nobody was fully aware of the hazards until just lately.

Do we blame General Motors for not putting seat belts in cars in 1960? No; the need for them just wasn't appreciated at the time. The same may be true of the Pentium. The goal of computer design is to get computers to function well. Good computer designers have trusted the users not to do wildly unreasonable things. Nobody foresees new developments in computer viruses, produced by criminals willing to work extremely hard to get other people's data.

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It's a book!

We proudly unveil the twelfth edition of our longest-running family project (actually started and led by our good friend Doug Downing, who was the best man at our wedding). For more than 30 years, we've been tracking down computer vocabulary and explaining it to people. More information at www.termbook.com.

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And a new tool for photographers

EXIFLOG is a free program that reads digital image files (from your camera) and gives you a text file listing the exposure data for each one. I use it all the time for astrophotography logs. Anybody who wants to make a checklist of pictures will find it useful.

The new edition includes all of Phil Harvey's ExifTool, which means it can read the metadata from almost any image file, whether or not it uses EXIF format, and supports every camera Phil Harvey has heard of.

Download and enjoy!

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C#: How to shell out to a command-line app and capture the output, in the background, in a Windows GUI application

I refer you to EXIFLOG, above, which does exactly that. Download the source code for version 3.1.

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Calendar musings

Happy new year! By now you've heard the hoax that 01/01/2018, 02/02/2018, 03/03/2018, etc., are all Sundays. That is not possible, of course, and even today isn't a Sunday. You'd think people would have noticed.

As I've mentioned before, some people are very gullible about the calendar because they haven't thought things through.

If I were teaching middle school, I would have sixth-graders make their own calendars. "Make a calendar for a year that starts on a Monday and is not a leap year." You can do that (except for the date of Easter) without looking anything up. It's not rocket science.

We say that a year is 52 weeks, but actually, 52 × 7 = 364 and a year is 365 days long (366 days in a leap year).

That means the weekday for any given date shifts forward 1 day at every year, and an additional 1 day when a leap year day intervenes. Today is a Monday; next New Year's Day will be a Tuesday. (The week runs too fast for the calendar, so to speak.)

Why don't we make a year exactly 52 weeks, by throwing away December 31 and doing away with leap year? Because a 364-day year would not stay in sync with the seasons. The orbital period of the earth is 365.2422 days. The shortest day of the year is December 21. If we had a 364-day calendar, then next year it would be December 22, and the next year December 23, and so on, gaining 1.2422 days per year, and in a century the dead of winter would fall in May and the heat of summer in December.

Even if we only did away with leap year, we would face a shift of a day every four years (nearly), which would get inconvenient after a while.

As it is, our present calendar makes the year 365.2425 days long in the long run, and that's not quite right. In about 3000 years we're going to need another adjustment, probably done by skipping a leap year day.

You may notice that some of the type on this page is slightly larger than it was last month. I am continuing to experiment with fonts. More changes may be coming, but at present, you are still looking at Google Arimo and Tinos.

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