Michael A. Covington    Michael A. Covington, Ph.D.
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Ichthys

Daily Notebook

Popular topics on this page:
Intervalometers (exposure timers)
How long can you expose without guiding?
Ashen Light of Venus explained
Evangelical statement about artificial intelligence
EX COEM CALLISTI
Astrophotos:
Moon (Aristarchus)
Moon (Grimaldi, Mare Orientale)
Jupiter
Jupiter
Jupiter (Great Red Spot breakup)
Corona Borealis
Many more...

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2019
June
20

Drama around the Great Red Spot

Picture

Last night we had unexpectedly clear weather around 11:30 p.m., and I got a telescope out, photographed Jupiter, and got this rather remarkable image.

You see the Great Red Spot in its current, shrunken state, brighter red than I can recall ever seeing it before, and also the effects of turbulence around it. The Great Red Spot has been spinning off material. That may be the cause of the dark streak that starts near it and continues to the right.

What you see in this picture has been confirmed by other observers with larger telescopes.

This picture was taken with a 5-inch telescope for two reasons. I started the observing session suddenly and didn't have much time for the telescope to equalize in temperature to the surrounding air, and a smaller, less massive telescope would do this faster. Also, Jupiter was low in the sky and I didn't expect the air to be steady, so I thought a smaller aperture would have an advantage, or at least less than the usual disadvantage compared to my 8-inch.

Stack of the best 75% of about 3000 video frames; Celestron 5 (vintage 1980), 3× extender, ASI120MC-S camera, processed with AutoStakkert, RegiStax, and Photoshop.

2019
June
19

Evangelical statement on artificial intelligence

I am one of the signers of a statement about the ethics of artificial intelligence recently adopted by the Ethics and Religious Liberty Commission (ERLC) of the Southern Baptist Convention.

You can read it here.

I wasn't involved in writing it; if I had been, it would have started with a definition of artificial intelligence. But I agree with what it says. Most of the sections of it elaborate the idea that we are responsible for what we do with our tools, even if the tools are designed to imitate autonomous human behavior. There is also an affirmation of the Christian view of marriage and a rejection of the use of computers to create high-tech pornography.

The ERLC has many wise things to say about social issues, and you may enjoy looking around their web site. Notably, they do not endorse Trump.



EXCOEMCALLISTI = EX COEM. CALLISTI

A friend recently asked me to translate the inscription EXCOEMCALLISTI on a small cross similar to this one.

Medieval Latin does not often stump me, but this one did. Obviously, it's EX something CALLISTI, "from the something of Callistus," and I ventured that it might be a souvenir of the Catacombs of St. Callistus (Calixtus).

But what is COEM? Obviously an abbreviation; a word immediately following EX would have to have a case ending other than EM.

An expert Latinist (Fr. John Zuhlsdorf) answered it for me. It's EX COEM[ETERIO] CALLISTI, "from the cemetery (i.e., catacombs) of Callistus."

I didn't get coemeterio because it was a borrowed Greek word — one I should have recognized because it's where we got cemetery.

And since the translation of EX COEM CALLISTI is nowhere on the Web, I'm recording it here.

2019
June
18

A structural change in American amateur astronomy

[Updated.]

Picture

I've written about how, after a long period of pulling apart, amateur and professional astronomy are pulling together again. For the story, click here.

Today an event has been announced that marks an important step in the pulling back together.

Sky and Telescope, the magazine that has held American amateur astronomers together since the 1940s, has been acquired by the American Astronomical Society (AAS), which is the leading organization of professional astronomers.

This may be a structural change in American amateur astronomy. Instead of being a purely commercial magazine, Sky and Telescope now has a new mission to fulfill. I expect it to continue doing what it does now, and also step into a new role of facilitating communication between professionals and amateurs.

Amateur astronomy pulled away from professional astronomy in the 1970s and 1980s because of technology — the professionals had CCDs, autoguiders, big telescopes, and big computers. Many of the amateurs chose to simply enjoy looking at the sky and stop trying to contribute to science.

Soon after the pulling apart started, a rival magazine appeared, Astronomy, focusing on distinctly amateur interests — celestial sightseeing, astrophotography, and the new abundance of commercially available equipment. It did an outstanding job of meeting amateurs where they were. Sky and Telescope at the time was employee-owned, closely associated with Harvard University, and addressed to both professionals and amateurs (for example, it reported on IAU meetings).

Competition, and, later, commercial ownership made Sky and Telescope become more and more like Astronomy, and that's where they still were a month or two ago — two increasingly similar magazines, with the same purpose, leaving readers wondering whether they could really support two.

But the nature of amateur astronomy has changed. Amateurs now have the same digital image sensors, computer power, and Internet as the professionals, and the amateur and professional observers are pulling back together. Sky and Telescope is undergoing the right change at the right time. Plans are for it to change very little, but under AAS sponsorship I have great hopes that it will move into a new niche and be more than just a hobby magazine.

2019
June
17

Just a bit of Mare Orientale

Picture

Attentive readers already know that I have made a minor hobby of photographing the small part of Mare Orientale that is sometimes visible from earth, depending on the moon's position in its (off-center) orbit and thus the angle from which we see it.

In this low-magnification picture, you don't see much of Mare Orientale, but the picture is a good guide to where to look. Roughly, Mare Orientale is on the lunar west (celestial east) edge of the moon's visible face, opposite Mare Crisium. The big dark crater toward the top of the picture is Grimaldi. The smaller dark one that is not too far inland from the arrow (but to which the arrow does not point) is Crüger.

Compare to what you see in the online edition of Rükl's lunar atlas (captioned in Italian).

Stack of the best 75% of 3470 video frames, Celestron 5 telescope (vintage 1980) at f/10, ASI120MC-S camera with clear UV-IR-block filter.



Smaller telescope, better Jupiter

Picture

When the air is unsteady, sometimes a smaller telescope has an advantage. Here's Jupiter last evening (June 16 here, June 17 in Greenwich Mean Time) through my 1980 Celestron 5, with a 3× extender (giving f/30) and an ASI120MC-S camera. Stack of the best 75% of 2610 video frames.

2019
June
15

The colorful moon

Picture

After two weeks of cloudy weather, I got my 8-inch telescope out in only slightly cloudy weather last night and took a picture of the lunar crater Aristarchus and the adjacent "seas" (maria, actually plains).

I've raised the color saturation in this picture so that you can see something that is barely visible to the eye through a telescope once it's pointed out to you: The moon is not colorless. The maria are browner in some places and bluer in others, reflecting the presence of different kinds of rocks.

Stack of the best 75% of 3471 video frames, Celestron 8 EdgeHD at f/10, ASI120MC-S camera. The moon was low in the sky, and the air was somewhat unsteady.



The not-so-great Red Spot

Picture

Here you see Jupiter and its satellite Europa. Europa's shadow is barely visible as a slight notch on the edge of Jupiter.

This is not a good picture — Jupiter was low in the sky, and the air was unsteady — but it's my first picture of Jupiter this season, and it shows something important: the Great Red Spot has continued to shrink. A few days ago, in fact, it threw off some red material, which other observers succeeded in photographing, and sat is a conspicuous "eye socket." The "socket" is less prominent now, according to what I see in high-quality pictures by others, but the Great Red Spot is less than half as wide as it was in the late 1800s, when astronomers started making exact drawings and measurements.

The Great Red Spot is an anticyclonic storm — a high-pressure area, a reverse hurricane — that has been going on for over 300 years. Why so long? Two reasons: Jupiter is really big, so everything should last longer, and Jupiter does not have seasons. That is, its axis is not tilted substantially away from its orbit, so its weather doesn't get interrupted, so to speak, by a seasonal cycle. There's no reason the Great Red Spot should last forever. It may even have gone away once already (in the 1700s and early 1800s) and come back again. Will I outlive it?

2019
June
8

Ashen Light of Venus explained

The latest issue of the Journal of the British Astronomical Association contains an article by Richard McKim which, in the middle of reporting observations, offers an explanation of the Ashen Light that I find convincing.

McKim, Richard (2019) The eastern and western elongations of Venus 2007-'17, Part II: The nocturnal hemisphere, JBAA 129:149-157. Not yet available in ADSABS but will be soon.

As you recall, Venus shows phases like the moon because it is close to the sun, so we usually see the sun lighting it from the side.

The Ashen Light is a glow sometimes seen in the unlit part of Venus. It resembles the earthshine that we see on the moon, but it is much fainter and has long been unexplained; there is nothing nearby to reflect light onto it.

Nobody sees the Ashen Light reliably. A few people have seen it occasionally. Many astronomers have considered it to be an optical illusion, the mind filling in the missing part of the circle. But there is now a much better explanation.

The Ashen Light is a well-known infrared phenomenon that occasionally reaches into the visible part of the spectrum so that human eyes can see it.

The surface of Venus is very hot, about 900° F, hotter than Mercury because of Venus's atmosphere. It is in fact at the threshold of being red-hot. It glows strongly in the infrared and is regularly photographed using infrared light.

On one fateful night in 2009, amateur astronomer Daniele Gasparri photographed the Ashen Light (through an infrared-blocking filter) and also photographed the unlit portion of Venus glowing in the infrared (at a wavelength of 1000 nm). It's obvious from the pictures that the two are the same phenomenon.

Even without the Gasparri observation, this explanation of the Ashen Light is highly credible. Very simply, Venus seems to be glowing faintly because it is glowing, but right at the limit of the human eye's spectral response. That means the Ashen Light is visible, or not, depending on the observer's eyes, the infrared transmission of the telescope, and conditions on Venus that might affect the temperature or the translucency of the atmosphere.

That explanation had already been proposed by astrophysicist Fredric W. Taylor in The Scientific Exploration of Venus (Cambridge, 2014). The Gasparri observation and other research cited by McKim support it.

This reminds me of how another Venus mystery was solved. A century ago, a major mystery for Venus observers was the existence of dusky shadings on the bright sunlit portion. Some observers saw them; some didn't. Debate raged.

By mid-century, it was established that the dusky shadings are real (and prominent) in ultraviolet light and the only question was whether they could be seen in visible light. They should have been more visible to younger observers (with more UV-sensitive eyes) using reflecting telescopes with inexpensive eyepieces (not much glass in the light path). So young amateurs actually had the best view! I never saw one, but one of my friends did, around 1970, and at the time we did not realize that the mystery had been solved by ultraviolet photography.

2019
June
6

The Northern Crown

Picture

One thing I like about the Aaron Memorial Lens (vintage 1971 Nikkor-H 50/2) is that it makes the bright stars stand out in pictures of the constellations. That is presumably because of a small amount of residual spherical aberration.

Here you see Corona Borealis (the Northern Crown), a stack of nine 2-minute exposures at f/4 with a Nikon D5500 at ISO 200 on an iOptron SkyTracker.



How long can you expose without guiding corrections?

My iOptron SkyTracker does not have any provision for autoguiding, so I need to know how long it will track the stars well enough without corrections. That of course depends on the focal length of the lens.

The picture of Corona Borealis above is part of a series of tests. What I do is photograph a star field 10 times, then analyze the eccentricity (misshapenness) of the star images using PixInsight.

With tiny star images and a digital camera, eccentricity never seems to go below an average value of 0.6. That's because stars don't hit pixels squarely. On the average, a star is very likely to be spread across two pixels in a random direction. As long as the direction is random, I don't mind.

So here are some histograms of eccentricity versus exposure time:

Picture

Here's what I think we learn from these:

  • You don't win 'em all. One or two out of the ten frames were poorly tracked even with short exposures. That is due to random irregularities in the tracking.
  • There is a sharp threshold at which the exposure time is suddenly long enough to span serious irregularities in the tracking. As we go up from 30 to 60 and then 120 seconds, performance is only slightly worse. But then, at 240 seconds, it's very bad.
  • The best exposure time with a 50-mm lens is 120 seconds or maybe a little less.

I will do the same test with a 105-mm lens soon.

2019
June
1

Intervalometers (exposure timers)

[Revised again.]

Picture
Click on picture to see this product on Amazon

Above you see an intervalometer (exposure timer). There seem to be two kinds on the market that look like this, each sold under many brands, and both have the same LCD display.

The difference? Type 1 is always on (always shows a display), defines "interval" as start-to-start (so that if you take two 15-second exposures at a 1-minute interval, they will start 1 minute apart), and times very accurately, not affected by temperature, although, curiously, the timing is slow by a factor of 1 in 600 (that is, 1 second per 10 minutes), which I think is a software bug.

Type 2 has to be turned on (awakened) by pressing a button, defines "interval" as the time between the exposures, and times much less accurately, with noticeable variation due to temperature (important to astronomers).

I have an old Type 1 (Phottix brand) for Canon and have just bought two Type 1 (Neewer brand) for Nikon.

I also had a Type 2 (Neewer brand, 2016 or so) that recently failed. It had a thin, flexible cable with interchangeable connectors for several kinds of cameras.

Its cable broke in 3 places and stopped me from doing astrophotography with my Nikons. That's why I decided to get 2 spares.

Picture

The electrical requirements for Canon and Nikon shutter control seem to be the same (more about that here and here). Canon uses standard 2.5-mm phone plugs on most of the newer cameras. Nikon uses a proprietary "DC-2" connector (shown above), which is not available as a standard electronic part. However, it is easy to get cables that have a DC-2 connector on one end and a phone plug (either 2.5mm or 3.5mm) on the other end (this, for instance). These are used for all sorts of camera remote controls. The phone plug has the same meaning as on Canons: connect ring to sleeve to autofocus; connect tip and ring to sleeve to take the picture; and on most cameras, do not connect tip to ring except when they are both being connected to sleeve.



Cough, cough...

Melody and I are both down with bronchitis, a very time-consuming ailment. The level of activity here will pick up as conditions permit.


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