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

Popular topics on this page:
Mars, with labels
Does Mare Crisium mean 'sea of crises'?
It's sapiens, not sapien
No, I'm not unemployed...
Schmidt-Cassegrain field curvature
Isaac Roberts, pioneer galaxy photographer
Telescope for sale (UPDATED)
The main point of astrophotography
Deep-sky observing in Latin
Astrophotography with just a DSLR and tripod
Moon (Mare Crisium)
Vega and Epsilon Lyrae
M31 (Andromeda Galaxy)
M57 (Ring Nebula)
Many more...
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(mainly telescope accessories)


Should opinions come in packages?

I am growing increasingly frustrated with being expected to adopt my views on all controversial issues as a package deal.

Consider abortion, gay marriage, gun control, deficit spending, and global warming. Why should my position on all five issues be the same? Yet the only positions that seem to be on the menu are yes-yes-yes-yes-yes and no-no-no-no-no.

The first one is called "liberal" and the second one is called "conservative," but pinning labels on them doesn't cause them to make any more sense. Is it at least conceivable that a person might think about each issue separately, or partly separately, from the others? Does a position on abortion really imply a position on global warming?

A human-subjects research scandal

One of the basic requirements of research ethics is that if people are deceived while being experimented on, you must reveal the deception to them as soon as possible afterward. Now it seems clear that, in this and other ways, Facebook and two universities performed unethical experiments by manipulating the emotional content of people's newsfeeds.

I don't know if regulations were broken — that depends on funding sources — but the National Academy of Sciences (which is non-governmental) should have mud on its face for publishing an unethically conducted study.

The experiment took place some time before October, 2013, but I am wondering if another one has been going on more recently. As you know, Facebook does not show you everything your friends post; that would be too much material to read. Instead it rates by popularity and especially by the amount of interaction you've had recently with each friend.

Well, in the past few days I've experienced a sharp rise in the amount of relatively boring, but mildly negative, material appearing in my newsfeeds from friends with whom I've had relatively little interaction. ("Boring" because it was about things I'm not involved in, not because my friends are dull.) It frustrated me to the point that I started "unfollowing" people (asking not to be shown their postings, which were things I wouldn't have expected to see in the first place). Are they experimenting again?


My old telescope is now in the showroom at Camera Bug, we've in the middle of a long spell of cloudy weather, and, anyhow, at the moment I'm down with a backache. (Just a good old-fashioned lower-backache, not anything spectacular.)

I've started looking at a history-of-astronomy question, the controversy about M102, and may blog about it later. It's unimportant as regards history as a whole, but important because of this vital question: Have I seen all of the Messier objects? I completed the list (as published by Mallas and Kreimer) over a quarter century ago, but I'm thinking I need to go and observe NGC 5866 (=? M102) just in case.


Astrophotography with just a camera and tripod

Can you do astrophotography with just a camera and tripod? YES, if the camera is a DSLR or possibly one of the better non-DSLR digital cameras with a large true aperture (not just a low f-number, but a large diameter lens) and a reasonably large sensor. This technique also works with a film SLR and ISO 800 or 1600 film (followed by digitizing the negatives and adjusting with Photoshop).

Using your fastest lens (50/1.8 or 28/2.8 is good), focus carefully manually (because autofocus can't see stars) and take a 5-second exposure of the starry sky. Use Photoshop (or other software) to adjust contrast and brightness (you won't see much until you do). If you like the results, try taking 50 such exposures and stacking them with DeepSkyStacker. For more information click here, here, here, and here.

In fact, the inspiration for my first astrophotography book was a film photograph of Orion that I took this way, on Fujichrome 100, in 1976.


You know that 6' means six feet, and 6'' means six inches. What does 6''' mean?

It means six "lines" or "lignes," i.e., 6/12 inch, or, later or in connection with guns, 6/10 inch.

I looked this up after reading D'Arrest's account of using the Mannheim telescope that was 73''' in diameter — that is, just over 6 inches.

Should I describe my 8-inch telescope as 8 inches, or as 20 centimeters, or as 0.2 meter, or as 96 lignes?


Reactivating the 300-mm lens

For the first time since I hurt my ribs and lost the ability to set up the Meade telescope back in October 2012, my Canon 300-mm f/4 lens has seen starlight.

Formerly, I used this lens piggybacked on the Meade telescope with the autoguider also piggybacked on the same telescope. Nowadays, I attach it to a dovetail bar and put it on the Celestron Advanced VX mount without a telescope. The autoguider, if present, rides upside down at the front of the same dovetail bar. I hope to post a picture of this setup later.

The very first starlight that the lens saw was the field of Vega and the double star Epsilon Lyrae, on the evening of June 17. This was a single 30-second exposure at f/6.3 through a bright, hazy sky. Conclusion: With PEC turned on, this mount usually (not always) tracks well enough for good 30-second sub-exposures with this lens.

I tried a lot more exposures and ended up doing a 10-minute exposure of the field of Antares and M4, with the autoguider turned on and the lens stopped down to f/10 to make such a long exposure possible under city lights. Here's what I got:

Tracking was very good. To show you how good, here's the central part of the picture, full-size; pixels on your screen correspond to pixels on the sensor.

Star images are round, showing that atmospheric turbulence or optics rather than tracking was the limiting factor, and are about 6 arc-seconds in diameter.


Here's an example of how video astronomy can reveal detail in an image captured under turbulent air. This is the best 900 of 1800 video frames captured on the evening of the 20th. (8-inch EdgeHD telescope, 3× Barlow lens, DFK camera.) The technique is explained here.


Some deep-sky observing in Latin

Serious galaxy and nebula observers who read Latin fluently — and I realize I might be the only one! — will enjoy Heinrich D'Arrest's Siderum nebulosorum observationes Havnienses, which I've just discovered (having dimly heard about it years ago). This book was published in 1867, making it one of the last important scientific books to be written in Latin. You can read it online here.

The full title, translated, is Copenhagen observations of nebulous stars, carried out at the university observatory through the 16-foot [long, 11-inch-aperture] Merz telescope from the year 1861 to the year 1867. The publisher's name, given as Typis Blanci Luni, is a bit of a puzzle. If you don't know quite enough Latin, it looks like "at the print-shop of the White Moon," but no, Blanci is not a Latin word at all (at least not until the late Middle Ages) and Luni is not a form of luna 'moon' (it could be the name of an obscure Roman moon-god). The same publisher also printed books about archeology. Maybe the name is an awkward Latinization of a Danish name.

I don't know exactly how D'Arrest pronounced his name, but presumably it was like D'Arrêt or D'Arré.

The purpose of the study was to discover more nebulae and to try to settle the question of whether they could all be resolved into stars. What D'Arrest did was simply look at the sky, looking for nebulae. He discovered a huge number (which we now recognize as galaxies) in Coma Berenices, Leo, and Virgo, as well as making scattered discoveries elsewhere and surveying the nebulae already known.

His descriptions are eloquent. In the part of a page that I reproduced above, columns give the catalogue designations of William Herschel and John Herschel (there was no NGC in those days), then the mean R.A. and declination for 1861, and then the nebularum facies et indoles 'appearance and character of the nebulae,' and finally the checklist number of the observing session, unless the date is given in the description itself.

In what you see above, D'Arrest describes Herschel I 280, which we now know as the galaxy NGC 6217, and then gives three descriptions of the globular cluster M12 from three different sessions. Here's a rough translation:

[NGC 6217:]

Bright enough, not at all small, with a stronger (brighter) nucleus; there exists, if I am not mistaken, a very faint little star in the nebulosity itself. I have not yet determined the position; I have therefore provided Herschel's; more recently (in 1866) Rümker II has also determined this nebula's position in the usual way. 1861 October 6.

Rümkerus II is Georg Friedrich Wilhelm Rümker, distinguished from Charles Rümker, who measured nebula positions also; I don't know what D'Arrest meant by cl. in front of his name. Note that all names have been given Latin endings to make it easier to distinguish their role in the sentence; in Latin, subject and object are distinguished by suffixes, not by word order. I take solerter to be a typo for solenter.

[M12, three observations:]

A cluster of Messier. Diameter in right ascension, 14 seconds. The faint stars in this conglomeration are well dispersed and irregularly arranged.

A huge multitude of tiny stars compactly situated together. The position [given in the R.A. and declination columns] is that of the densest part. The things Sir John Herschel says about the visible structure of this cluster seem to square well with the way it looks. [Observed] with the sky brightening [after dawn].

A very elegant cluster of stars, about 6 arc-minutes [in diameter]; richer indeed in the middle, but lacking a real nucleus. Contains a crowd of small stars from magnitudes 11 to 20.

And before you ask, no, I don't expect to have time to translate the rest of the book! But it would be handy if someone did.


Why astrophotography is better than looking through a telescope

My old friend Mike Gay asks that I say, more emphatically, just what makes astrophotography so great.

It's this: The camera can accumulate light during a long exposure and reveal things that are too dim to see with any telescope.

Consider again this picture of the Andromeda Galaxy:

Important point: You can't get this view through any telescope in the world, not even the largest. (Especially, in fact, not the largest.) The reason is that the outer parts of the galaxy are too dim for the human eye to see.

For the Andromeda Galaxy, you don't need magnification. It already covers a patch of sky about eight times the size of the full moon! (You can verify this with binoculars under a dark country sky.)

What you need is brightness. The details in the spiral arms are just too faint for the human eye to see, and binoculars or a telescope do not make them brighter.

Think about it. Telescopes don't magnify the brightness of surfaces. If they did, you'd hurt your eyes trying to use binoculars on a sunny day. No; telescopes bring out more stars but do not make surfaces (extended objects) brighter. The telescope collects more light but spreads it over a larger area. The pupil of your eye sets a limit to the size of the light beam that the telescope can deliver, and what it implies — if you do the optical calculations — is that a telescope can't magnify brightnesses.

That's why most of the spiral structure in galaxies — along with faint nebulae and similar objects — is much easier to photograph to see. Much of it is impossible to see.

And that's why astrophotography is not just fun, it's scientifically important.



Telescope for sale (UPDATED)


(1) If not sold by Saturday, June 27, this telescope will be placed on consignment with Camera Bug (www.camerabug.com) in Atlanta. [It is there now.]

(2) This is about 70 pounds of equipment (telescope 45 pounds, telescope 25 pounds) and the cost of packing and shipping is prohibitive. The buyer should plan to pick it up from me or, after June 27, from Camera Bug.

(3) This is a very full-featured instrument, and if you're new to astronomy, you have a learning curve ahead of you. It may be a very enjoyable learning curve... it was for me.

I am selling my vintage-2000 Meade LX200 telescope, an 8-inch f/10 Schmidt-Cassegrain. It has Meade's first generation of "go to" (computerized pointing) technology, meaning that you can use it in alt-azimuth or equatorial mode and have it find celestial objects for you, once you've aligned it on a star. Because it's first-generation, you should align ("sync") on a bright star in the area of the sky where you want it to find objects accurately.

This is the very telescope that led me to write How to Use a Computerized Telescope, which describes it in detail. A copy of that book is included with it.

It also includes this electrical improvement and this homemade equatorial wedge (very sturdy, but only for latitude 34 north, give or take a couple of degrees).

Included also is a 12-volt line power supply. I have never used this telescope on 18 volts (as Meade originally said to) and have heard that there is an increased risk of burning out the motors or their voltage regulators if you do.

Complete configuration:

Telescope on computerized fork mount
Upgraded internal focuser
8×50 finderscope
Tripod with homemade wooden equatorial wedge
Hand control box (some wear visible, but fully functional)
Spare cables for hand box and declination motor
Power supply (for powering it from 120-volt AC line) with cable
Computer cable (for controlling with your computer if you wish)
Visual back for standard 1.25" eyepieces
Mirror diagonal for standard 1.25" eyepieces
Two inexpensive eyepieces (Bausch & Lomb 18mm and 30mm)
Instruction book (from Meade)
Polar alignment instruction chart
1 copy of How to Use a Computerized Telescope
1 piggyback camera mount, presently installed at rear top, can be moved

Please e-mail me for the price, which is lower than you'd think. Purchaser must pick it up in Athens, Georgia (75 miles east of Atlanta).

I have quite a few additional accessories that will be put on the market separately, including a 2-inch back, 2-inch diagonal, 2-inch 40-mm eyepiece, and Crayford focuser. But my cameras, autoguider, and other accessories have been transferred to the Celestron EdgeHD.


Isaac Roberts, pioneer galaxy photographer

In 1899, British astrophotographer Isaac Roberts self-published a book of his pictures and presented a copy to The University of Georgia, complete with a handwritten note. Last Sunday afternoon, while browsing in the Science Library, I found it. It was catalogued as a folio but had been misshelved among ordinary-sized books about star clusters and nebulae. Since I've been avidly photographing clusters and nebulae myself for 40 years, I was surprised to see an old book about them that didn't look familiar. I pulled it out and took a closer look.

Roberts was a wealthy industrialist who took up astronomy as a hobby and had a 20-inch telescope in an observatory — that is, he was almost as well-equipped as our University, which has a 24-inch, and he had a better location.

Isaac Roberts' special interest was "spiral nebulae" (no one knew at the time that they were galaxies). In fact, he was the first person ever to take a picture that looked like this:

That's the Andromeda Galaxy (M31), of course, and Roberts' first picture of it was deposited with the Royal astronomical Society in 1889 — this is one of his later and better ones.

Nowadays, that view of M31 is one of the icons of astronomy, but in the 1890s, it was brand new. You can't see that scenery through any telescope, no matter how big. It relies on the ability of photographic film to accumulate light. Roberts made time exposures as long as 12 hours on photographic plates.

The galaxy looks more or less the same no matter who photographs it, and below you see my own humble attempt from October 2007. The difference is that I used only three inches' aperture and an exposure of only 12 minutes, total, on a digital image sensor instead of a photographic plate.

Roberts also photographed many other galaxies and nebulae, making astrophysical discoveries right and left because he was the first person ever to get good images of these objects.

His 1899 book is actually half of a two-volume set, now available as a reprint from Cambridge University Press. The second volume is free on line, in somewhat imperfect PDF form, at Archive.org, here.



The air was reasonably steady on the evening of the 14th and, in between clouds, I got an image of Saturn. 8-inch EdgeHD, 3× Barlow lens, DFK camera, best 900 of 1800 video frames, stacked and processed with Autostakkert, RegiStax 6, and PixInsight.

In this picture you can at least begin to see some peculiarities of Saturn that were once thought to be observers' mistakes. The rings aren't quite the same on the left side as on the right side — look at subtle detail in them. That's caused by subtle gravitational effects from the satellites of Saturn. For decades, though, everyone took it for granted that any mismatch must be an illusion. They were wrong.

Schmidt-Cassegrain field curvature

Most amateur telescopes today are compact Schmidt-Cassegrains with an f/2 primary and f/10 overall focal ratio, descendants of the Celestron 8 of 1973. (That includes my Meade LX200.) As is now well known, the Schmidt-Cassegrain gives a sharp image at the center of the field but suffers serious off-axis aberrations. So do Newtonians, medium-focal-length Cassegrains, and other astronomical telescopes. It doesn't matter because we're only looking at the center of the field when we use high power. Wide-field photography, of course, is different.

The two main off-axis aberrations are field curvature and coma. Celestron's EdgeHD design corrects both. Meade's ACF design and the Ritchey-Chrétien design used at observatories correct only coma (field curvature is not so serious in a larger telescope).

By now it is well known that the focal surface of an 8-inch f/10 Schmidt-Cassegrain is curved with a radius of about 11 inches, i.e., about like a beach ball. The exact radius depends on where you choose to put the focal plane; most telescope accessories put it about 105 mm behind the rear flange, and that appears to be a design parameter.

But there's another fact about field curvature, easily overlooked, but made clear by Rutten and Van Venrooij in Telescope Optics: field curvature is almost completely swamped by coma. That is, coma is so predominant that the field curvature would be hard to measure experimentally. That's one reason not to worry about it so much. It becomes a real concern in the Ritchey Chrétien and Meade ACF, which do not have another aberration masking it.



I've been doing a major cleaning out of my telescope cabinet, preparing to sell the Meade LX200 that has served me so long and so well. The cabinet now holds my 8-inch Celestron EdgeHD and my vintage 1980 orange-tube Celestron 5. The latter now sports the big 9×50 finderscope that came with the EdgeHD. (It fits and even allows the tube to swing through the fork arms.)

Here are this afternoon's sunspots, photographed with the Celestron 5 and a Thousand Oaks solar filter. This is a stack of four 1/2000-second exposures, combined and enhanced with RegiStax.

And also retouched. There was a "dust doughnut" from dust on the sensor, just to the upper right of center, below the intricate group of small sunspots. I retouched it out. That means this picture has no scientific value — at least, that part of it doesn't! It no longer tells you whether there were sunspots in that position. You can take my word that there weren't, as far as I could tell.

Celestron Advanced VX Mount technical notes

The counterweight shaft is exactly 20 mm in diameter. Counterweights for the iOptron iEQ30 fit it perfectly. That is how I've obtained a 2-kg counterweight which, in addition to the supplied 5.5-kg counterweight, gives me additional versatility.

The power connector is a DC coaxial plug, 5.5 mm o.d., 2.0 or 2.1 mm i.d. (those are the same size, quoted different ways by different manufacturers due to rounding of what was originally an inch dimension, as I understand it). The Switchcraft S761K connector fits it. You can also use readly available 5.5×2.1-mm plugs (e.g., from Radio Shack) that lack the locking nut. Positive is center. I do not know if the telescope is protected against reverse polarity.


No, I'm not unemployed...


A year after changing careers, the biggest misconception I have to deal with is that people hear the word "retired" and assume I'm not working.

It's true that I left the University of Georgia as a retiree. But I am very much in business and working as much as I can.

Covington Innovations is not an empty ambition, a fantasy, or a tax dodge for my hobbies. It is an active consultancy with four current clients, one of which provides most of the work, and with the opportunity to take on more clients whenever I have the time. I am doing a confidential software development project for the largest client; helping develop patents for two others; and participating in a medical research project. The work is important, but I can't tell you a lot about it. Some of it contributes to the defense of the United States; some of it may prevent the next economic crisis; and some of it helps conquer a dreaded disease.

I don't work full-time at the moment because I have substantial family obligations. Melody has just had one hip replaced and is getting ready for the other one. She can't drive at present, so I work from home a lot and don't travel. I am very much enjoying getting to spend so much time with her. She has been my best friend as well as my beloved for nearly four decades.

But I am not on the golf course or lounging in front of the TV set. Although I am finding some time for astronomy and electronics, I have to manage my time carefully.

In fact, a big difference between academic life and business life is that UGA was paying me to do research on whatever I wanted — which meant that invitations and suggestions were welcome — but as a consultant, I only get paid for research that clients specifically need. So only a limited amount of time is available for unfunded work, and it competes directly with personal leisure.

As a consultant, I'm not on a salary; I only get paid for work actually done. This means goofing off at work is basically impossible. Taking time off means giving up income — invariably.

Nor do I want to get overworked and exhausted. That's why I don't jump at the chance to add activities every time someone suggests something.

In fact, the older I get, the more I realize that I have only a limited number of years of work left. Maybe as many as thirty, but still a limited number. At the same time, I am very productive because of past years' experience. So I proceed deliberately. If something is worth doing (for income or for personal reasons), I make plans to do it, and if not, I make plans not to do it. I'm not casting about randomly for ways to fill up the idle hours. Every decision to do something is ipso facto a decision not to do numerous other things.

That's why I can't chat on Facebook all day, take a day off on short notice to do something somebody has invited me to do, or (above all) do large amounts of work free just because somebody thought I'd enjoy doing it (for them).

The bottom line? I care about everybody and don't want to slight anyone. But I am running a business and can't take time off casually, and I hope nobody feels slighted because I'm tending to my business.


M57 in EdgeHD

Here you see what I got by choosing a Celestron EdgeHD telescope instead of a conventional Schmidt-Cassegrain design. This is the entire field of a Canon 60Da at the EdgeHD focal plane. Notice that the stars are as sharp at the corners as at the center. Unlike almost all the pictures through a telescope that I've ever released, this one is not cropped.

What you see in the middle is the Ring Nebula (M57). This is a stack of thirteen 30-second exposures at ISO 2000. I could have taken considerably longer exposures but did not know, at the time, whether to trust my autoguider.


It's sapiens, not sapien

Peeve of the day: People who try to spell Homo sapiens without the final s.

That s is not a suffix. It is part of the word, and when you leave it out, the word is just misspelled.

Homo sapiens is Latin for 'intelligent human being.' The plural, 'intelligent human beings,' would be homines sapientes.

Incidentally, Latin homo 'human being' is unrelated to the Greek prefix homo- 'same' that is so common in scientific terminology.

Tongue twister

Listening to the radio the other day, I realized that one thing Franklin D. Roosevelt gave America was a tongue twister.

Plenty of people pronounce Social Security as Sosal Security. In fact, even the collapsed form Sosecurity is moderately common. I hear these from people who deal with Social Security professionally, not just from people encountering it from the first time.

I never hear those altered pronunciations of social in other contexts (e.g., social life, ice cream social). People may not even recognize it as the same word — Social Security is, after all, political jargon.


Does Mare Crisium mean 'sea of crises'?

The large, dark lunar "sea" (actually plain) that you see in this picture is called Mare Crisium, traditionally translated "Sea of Crises." The name was given to it by Riccioli in 1651 (click here to see his map). I haven't read his whole Almagestum Novum to see if he gives a reason for the name anywhere, but a quick skim tells me only that he is making a point of not naming lunar features after terrestrial ones.

Mare Crisium definitely means a sea of whatever crisis meant at the time. But crisis has not always meant what it means today. It is a Greek word borrowed into Latin and hence known in all the languages of Europe. In Greek, it meant 'judgment.' In medieval and Renaissance medicine, it meant the point in the course of a disease where it becomes possible to judge whether the patient will recover — that is, the turning-point. Later it also meant a political turning-point. In very recent years, since 1900, it has come to mean 'urgent situation' as it does today.

So do not think of Mare Crisium as a sea of "crises" in the modern sense. Think of it as more likely commemorating medical expertise; it is, after all, between two highlands that Riccoli named Terra Vitae and Terra Vigoris ("Land of Life," "Land of Strength"), names that did not stick.

The picture is a stack of about 1800 out of 3600 video frames taken with a DMK camera, IR-pass filter, and Celestron EdgeHD 8-inch telescope.


Mars, labeled

WinJupOS users: Now you can generate a map of Mars with the major features labeled, showing the planet rotated exactly to match your photograph or drawing. Just download this file and specify it as the "texture" of Mars in WinJupOS.

This is, of course, just a quick map to help you get oriented with a more detailed map. It labels features with the "old" nomenclature, except for Valles Marineris, which I've included under its new name.

[Afterthought:] I think "Valles Marineris" is very bad Latin. "Mariner" is not a foreign name with no evident etymology; it is derived from Latin and they should have used the Latin word from which it came, marinarius. Then we would have had Valles Marinarii. Is it too late to change?

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