History – Cosmic Reflections

Constellations Old and New

The celestial sphere is a jigsaw puzzle with 88 pieces. The oldest piece is arguably the constellation Ursa Major, The Great Bear. Based on historical writings, prehistoric art, and the knowledge that this group of stars represented a bear in many cultures scattered throughout the world leads scholars to believe that this constellation was first described around 11,000 B.C., perhaps earlier.

The newest constellations are the 17 listed in the table below. Thirteen of these were invented by French astronomer Nicolas-Louis de Lacaille (1713-1762) during his stay at the Cape of Good Hope in 1751 and 1752, and the other four (Puppis, Pyxis, Vela, and Carina) are portions of the ancient enormous constellation Argo Navis, described by Ptolemy (c. 100 – c. 170). Though all of these constellations reside completely in the southern hemisphere of the sky (and thus can be best observed in the southern hemisphere), all but two of them (Mensa and Octans) have a portion that rises above the southern horizon as seen from Tucson, however scant and brief.

Newest Constellations

Constellation	Description	Declination
Puppis	The Stern (of Argo Navis)	-51˚ to -11˚
Pyxis	The Compass (of Argo Navis)	-37˚ to -17˚
Fornax	The Laboratory Furnace	-40˚ to -24˚
Antlia	The Air Pump	-40˚ to -25˚
Sculptor	The Sculptor's Workshop	-39˚ to -25˚
Caelum	The Sculptor's Chisel	-49˚ to -27˚
Microscopium	The Microscope	-45˚ to -27˚
Vela	The Sail (of Argo Navis)	-57˚ to -37˚
Horologium	The Pendulum Clock	-67˚ to -40˚
Norma	The Carpenter's Square	-60˚ to -42˚
Pictor	The Painter's Easel	-64˚ to -43˚
Telescopium	The Telescope	-57˚ to -45˚
Carina	The Keel (of Argo Navis)	-76˚ to -51˚
Reticulum	The Net	-67˚ to -53˚
Circinus	The Compasses	-71˚ to -55˚
Mensa	The Table Mountain	-85˚ to -70˚
Octans	The Octant	-90˚ to -74˚

Which (mostly) northern constellations were added last? Around 70 years prior to Lacaille, Johannes Hevelius (1611-1687) described the seven constellations in the table below. These constellations were first published posthumously in 1690.

Newest More Northerly Constellations

Constellation	Description	Declination
Lynx	The Lynx	+33˚ to +62˚
Lacerta	The Lizard	+35˚ to +57˚
Canes Venatici	The Hunting Dogs	+28˚ to +52˚
Leo Minor	The Lion Cub	+23˚ to +41˚
Vulpecula	The Fox	+19˚ to +29˚
Sextans	The Sextant	-12˚ to +6˚
Scutum	The Shield	-16˚ to -4˚

Let us now return to the oldest constellation, Ursa Major. The earliest extant literary work describing the constellations, including Ursa Major, is Phainómena by the Greek didactic poet Aratus (c. 315 BC – 240 BC). Phainómena is based on an earlier work by the Greek astronomer and mathematician Eudoxus of Cnidus (c. 408 BC – c. 355 BC), now lost. Earlier, the Greek poets Homer and Hesiod (~700 BC) mentioned the constellations, and we know that the Babylonians had a well-developed system of constellations (~2000 BC), as did the Sumerians even earlier (~4000 BC), later assimilated by the Greeks.

Here is what Aratus says in Phainómena about Ursa Major, in context.

The numerous stars, scattered in different directions, sweep all alike across the sky every day continuously for ever. The axis, however, does not move even slightly from its place, but just stays for ever fixed, holds the earth in the centre evenly balanced, and rotates the sky itself. Two poles terminate it at the two ends; but one is not visible, while the opposite one in the north is high above the horizon. On either side of it two Bears wheel in unison, and so they are called the Wagons. They keep their heads for ever pointing to each other's loins, and for ever they move with shoulders leading, aligned towards the shoulders, but in opposite directions. If the tale is true, these Bears ascended to the sky from Crete by the will of great Zeus, because when he was a child then in fragrant Lyctus near Mount Ida, they deposited him in a cave and tended him for the year, while the Curetes of Dicte kept Cronus deceived. Now one of the Bears men call Cynosura by name, the other Helice. Helice is the one by which Greek men at sea judge the course to steer their ships, while Phoenicians cross the sea relying on the other. Now the one is clear and easy to identify, Helice, being visible in all its grandeur as soon as night begins; the other is slight, yet a better guide to sailors, for it revolves entirely in a smaller circle: so by it the Sidonians sail the straightest course.

Between the two Bears, in the likeness of a river, winds a great wonder, the Dragon, writhing around and about at enormous length; on either side of its coil the Bears move, keeping clear of the dark-blue ocean. It reaches over one of them with the tip of its tail, and intercepts the other with its coil. The tip of its tail ends level with the head of the Bear Helice, and Cynosura keeps her head within its coil. The coil winds past her very head, goes as far as her foot, then turns back again and runs upward. In the Dragon's head there is not just a single star shining by itself, but two on the temples and two on the eyes, while one below them occupies the jaw-point of the awesome monster. Its head is slanted and looks altogether as if it is inclined towards the tip of Helice's tail: the mouth and the right temple are in a very straight line with the tip of the tail. The head of the Dragon passes through the point where the end of settings and the start of risings blend with each other.

DNA Genealogy

DNA sequencing is revolutionizing the study of human origins and prehistory, but also genealogy.

The number of ancestors you have at each preceding generation is given by 2ⁿ, where n = 1, 2, 3, and so on (parents, grandparents, great-grandparents, etc.). The total number of ancestors you have back to any preceding generation is given by 2ⁿ⁺¹ – 2. The number of ancestors for the first seven generations is shown in the following table.

Generation	n	Generation Ancestors	Cumulative Ancestors
Parents	1	2	2
Grandparents	2	4	6
Great-Grandparents	3	8	14
2G-Grandparents	4	16	30
3G-Grandparents	5	32	62
4G-Grandparents	6	64	126
5G-Grandparents	7	128	254

It is natural to wonder, is there a point at which you don’t receive any distinguishable¹ DNA from an ancestor? As an example, looking at your 128 great-great-great-great-great-grandparents, what are the chances that any one of them contributed no DNA to you? The answer is about 0.5%. You would expect, on average, that 128×0.005 = 0.64 ancestors at this generation has contributed nothing to your DNA. In other words, either 127 or 128 of your 5G-grandparents contributed to your DNA. As we go even further back in time, the number of ancestors at each preceding generation that did not contribute to your DNA rapidly increases, as shown in the following table.

Generation	n	Generation Ancestors	Likelihood of inherited DNA
Parents	1	2	100%
Grandparents	2	4	100%
G-Grandparents	3	8	100%
2G-Grandparents	4	16	100%
3G-Grandparents	5	32	100%
4G-Grandparents	6	64	99.99%
5G-Grandparents	7	128	99.5%
6G-Grandparents	8	256	96%
7G-Grandparents	9	512	84%
8G-Grandparents	10	1024	64%

So you can see that of your 1,024 G-G-G-G-G-G-G-G-grandparents, you will not have received any DNA from about 1024×0.36 = 369 of them.

Another question you might have relates to cousins. What is the probability that you and a cousin share DNA? That is shown in the following table.

Relationship	Likelihood of a DNA Match
Sibling	100%
1st Cousin	100%
2nd Cousin	100%
3rd Cousin	98%
4th Cousin	71%
5th Cousin	32%
6th Cousin	11%
7th Cousin	3.2%

As you can see, beyond your 3rd cousins, there’s a reasonably good chance you have no distinguishable DNA in common.

DNA Tests

The usual DNA test that most folks get is an autosomal DNA test. It is that test that we are referring to in the sections above.

There are two other DNA tests you might want to consider. The Y-DNA test and the mtDNA test, which allow you to trace your patrilineal (father) and matrilineal (mother) lines, respectively.

Y-DNA Tests

A Y-DNA test looks at the Y-chromosome, which only men have. The Y-chromosome is passed down from father to son generation after generation virtually unchanged. So if you are male and took the Y-DNA test, and another male also took the Y-DNA test, if they matched you would know that you are both descended from the same common ancestor along male lines, whether it could be proved by records or not. I’ll use myself as an example.

I have been able to trace my male line ancestors back to my 7G-grandfather.

Ancestor	Relationship
Andreas Oesper (?-1721)	7G-Grandfather
Andreas Oesper (1709-1776)	6G-Grandfather
Zacharias Oesper (1744-1792)	5G-Grandfather
Johann Georg Oesper (1780-?)	4G-Grandfather
Johann Peter Oesper (1817-1890)	3G-Grandfather
Ernst William Oesper I (1846-1918)	2G-Grandfather
Ernst William Oesper II (1874-1951)	Great-Grandfather
Ernst William Oesper III (1904-1976)	Grandfather
Ernst William Oesper IV (1928-1997)	Father
David Oesper (1956-)	Self

Any male that descended along the male line from any of these ancestors (or unknown earlier generations) would have a Y-DNA match with me. They probably also have the surname Oesper, but not necessarily for a variety of reasons.

Though we haven’t both taken a Y-DNA test, my 2nd cousin once removed Pete Oesper and I would have matching Y-chromosomes. Pete is descended along the male line from my great-great-grandfather Ernst William Oesper I.

mtDNA Tests

A mitochondrial DNA (mtDNA) test looks at the mitochondria, which both males and females have. Mitochondrial DNA is passed down from a mother to her children generation after generation virtually unchanged. So if you and another person took a mtDNA test, if they matched you would know that you are both descended from the same female ancestor along mother-lines, whether it could be proved by records or not. I’ll again use myself as an example.

I have been able to trace my female line ancestors only back to my great-grandmother, or perhaps my great-great-grandmother, but all we have for her is a first name and perhaps not even that.

Ancestor	Relationship
Mary? (?-?)	2G-Grandmother
Katherine Curtin (1855-1931)	Great-Grandmother
Sarah Geneva Smith (1896-1992)	Grandmother
Carla Mary Pieroni (1929-1985)	Mother
David Oesper (1956-)	Self

My great-grandmother Katherine Curtin and her brother and sister were orphaned at a young age in New York City. We know that her parents immigrated from Ireland, but nothing more for certain. If I were to take a mtDNA test and could find someone in Ireland who is a mtDNA match, they would likely have descended along the female line from the same female ancestor as me, presumably my great-great-great grandmother, or her mother, grandmother, etc. See how it works?

¹ All humans have about 99.5% identical DNA. The half percent that differs between us is what we might call traceable or distinguishable DNA. When you see the term DNA in this article, we are always referring to the portion of the human genome that is distinguishable between individuals, present and past.

References

What is genetic inheritance?
https://www.ancestry.com/cs/dna-help/matches/inheritance
Accessed: November 17, 2021

Y-DNA, mtDNA, and Autosomal DNA Tests
https://support.ancestry.com/s/article/Y-DNA-mtDNA-and-Autosomal-DNA-Tests?language=en_US
Accessed: November 17, 2021

Acknowledgements

I’d like to thank Paul Martsching for emails he sent to me that I utilized in the writing of this article. I alone am responsible for any errors or inaccuracies herein, so please let me know if you find anything in need of correction.

Why Did It Take a Telescope to Discover the Orion Nebula?

Using the newly-invented telescope, French astronomer Nicolas-Claude Fabri de Peiresc (1580-1637) discovered the now-famous Orion Nebula (M42) when he was 29 years old, 410 years ago on this day.

November 26, 1610.

But wait a minute. You and I can see a nebulous “star” below the belt of Orion with our unaided eyes under a reasonably dark sky. Why wasn’t this object discovered long before the invention of the telescope?

Apparently, there is no known report of a “nebulous star” in the sword of Orion prior to Peiresc’s discovery. Is the Orion nebula brighter now than it was a few centuries ago? Is it possible an earlier observational report somehow got missed or was not properly interpreted?

There is speculation that the Maya civilization of Mesoamerica recognized the Orion Nebula long before Peiresc’s discovery, describing it as smoke from the smoldering embers of creation.

One can only stand in wonderment at the knowledge and experiences of hundreds of generations of men, women, and children who are utterly unknown to us today. Passed from person to person and generation to generation through oral tradition, never written down and eventually lost. Or written down on documents that later disintegrated or were purposefully destroyed.

Who hasn’t wished that they could could time travel back to the past? Have you ever wondered what your current location looked like a hundred years ago? A thousand years ago? Ten thousand or more years ago? Though sending humans into the past will probably never be possible, who’s to say that we won’t eventually figure out a way to view and perhaps even hear the past, without actually being there or having the ability to change it?

John Brashear: A Man Who Loved the Stars

Pittsburgh telescope maker, optician, and educator John Alfred Brashear (1840-1920) was born 180 years ago this day. His world-renowned optical company made much of the astronomical equipment in use in the United States during the late 19th and early 20th centuries. His works included a 30-inch refractor for Allegheny Observatory in Pittsburgh, a 15-inch refractor for the Dominion Observatory in Canada, and the 8-inch refractor at the Drake University Municipal Observatory in Des Moines, Iowa.

My good friend, telescope maker Drew Sorenson in Jefferson, Iowa, has been a fan of John Brashear for many years. Not only does Drew make fine refractors as did Brashear, but there is more than a little resemblance between the two men. Drew introduced me to a delightful book entitled John A. Brashear: The Autobiography of A Man who Loved the Stars, which was first published posthumously in 1924. For anyone interested in the history of astronomy and the life of a scientist and humanitarian who struggled from near-obscurity to great success with only an elementary school education, this book is a must-read.

Here are three of my favorite passages from the book.

Somewhere beneath the stars is work which you alone were meant to do. Never rest until you have found it.

There is another yarn I cannot resist telling. The young farmer who had been bringing Mrs. Brashear her supply of vegetables asked her one day if I would let him look in the big telescope if he came up some clear evening. She encouraged him to do so, and I found him waiting one night to see the sights. I did not know whether or not he had any knowledge of astronomy, but I asked him what he would like to look at. He replied, “Juniper.” I told him that unfortunately that planet was not visible in the sky at the time. Then he expressed a desire to see “Satan.” But his Satanic Majesty was not around either. The climax came when he asked if I could show him the “Star of Jerusalem!” I ended it by showing him the moon and some clusters, and he went home very happy.

I remember, too, an old gentleman over eighty years of age who climbed the hill one moonlight night for a look in the telescope. The good man was utterly exhausted when he reached the house, and Ma and I had him lie down on the lounge to rest before climbing the stairs to the telescope. The views that night were fine, and I can hear the soliloquy yet of the dear fellow as he said, “For many years I have desired to see the beauties of the heavens in a telescope. I have read about them and heard lectures about them, but I never dreamed they were so beautiful.” We invited him to stay all night; but as it was moonlight, and much easier for him to go down the hill than to come up, he insisted on going home. I went part of the way with him to see that he got along all right; and all the way he expressed his delight at having the wish of a lifetime gratified that night.

Three weeks later the funeral cortège of that old man passed along the road on the opposite hillside that led to the cemetery, and it has always been a pleasure to remember that I was able to be of some service in gratifying one of his desires of a lifetime.

I think that all my life I have been partial to old people and children, and it has always been a source of genuine pleasure to contribute to their happiness.

John A. Brashear: The Autobiography of A Man who Loved the Stars (1924)

First Photograph of the Orion Nebula

Henry Draper (1837-1882)

On this date 140 years ago, American physician and prominent amateur astronomer Henry Draper (1837-1882) made the first successful photograph of the Great Nebula in Orion, now usually referred to as the Orion Nebula. He used an 11-inch telescope (an Alvan Clark refractor!) and an exposure time of 50 minutes for the black and white photograph.

First photograph of the Orion Nebula, September 30, 1880. (Henry Draper)

Draper continued to improve his technique, and a year and a half later he obtained a 137-minute exposure showing much more detail.

Photograph of the Orion Nebula, March 14, 1882. (Henry Draper)

It really is amazing how image recording technology has improved over the past century and a half! At its best, film-based photography had a quantum efficiency of only about 2%, which means that only 2 out of every 100 photons of light impinging on the photographic medium is actually recorded. The rest is reflected or absorbed. The human eye—when well dark adapted—has a quantum efficiency of 15% or better, easily besting photography. Why, then, do photographs of deep sky objects show so much more detail than what can be seen through the eyepiece? The explanation is that the human eye can integrate photons and hold an image for only about 0.1 second. Film, on the other hand, can hold an image much longer. Even with reciprocity failure, photographic media like film can collect photons for minutes or even hours, giving them a big advantage over the human eye. But charge-coupled devices (CCDs) are a considerable improvement over older technologies since they typically have a quantum efficiency of 70% up to 90% or more. The CCD has truly revolutionized both professional and amateur astronomy in recent decades.

Recent Orion Nebula CCD image by Robert Gendler

Lunar Maria

António Cidadão, of Oeiras, Portugal, many years ago produced a wonderful set of images showing the location of each mare on the Moon. His website has not been updated since 1999 and the contact email address provided there is no longer valid, and even after a thorough Google search I can find no way to contact him to ask permission to link images here to his site. Even worse, because his hosting site is not secure (http: instead of https:), WordPress does not allow me to link directly to his images so I had to put copies into my media library. Please know that the images shown below are all copyrighted by António Cidadão.

Each image shows north is up and west is to the left. This is direction of increasing longitude and therefore west on the Moon, but in our sky, east is to the left. In other words, these annotated images of the Moon are correctly oriented as they would appear to the unaided eye in the sky in the northern hemisphere. In the rest of this article, we will use the moon-centric east-west convention that Cidadão indicates in his image diagrams.

Let’s take a look at each of the lunar maria from moon-west to moon-east. Their fanciful names were mostly given (and codified in 1651) by the Italian astronomer Giovanni Battista Riccioli (1598-1671). Riccioli chose names related to weather, as it was then believed that the Moon, the closest celestial body to the Earth, exerted an influence on the Earth’s weather. This is perhaps not at all surprising given that the phenomenon of tides had been known since antiquity.

Most of the nearside west portion of the Moon is covered by a mare that is so large that it is given a unique designation: Oceanus for “ocean”.

Oceanus Procellarum, the “Ocean of Storms”

Oceanus Procellarum contains the famously bright crater Aristarchus and the associated Aristarchus Plateau. In the image above you will notice what appears to be a tiny mare close to the limb of the Moon west of the southern part of Oceanus Procellarum. This is the lava-flooded crater Grimaldi.

South of Grimaldi and straddling the lunar limb is Mare Orientale. It is difficult to see because most of it is on the lunar farside, though libration can sometimes bring its oblique visage into view. The name Orientale, meaning “eastern”, describes its location on the eastward-facing limb of the Moon as seen from Earth, rather than its westward direction as seen from the surface of the Moon.

Mare Humorum is located just south of Oceanus Procellarum. It is round and inviting, though no spacecraft has ever landed there.

Mare Nubium is east of Mare Humorum. The large crater Bullialdus flanks the western edge of Mare Nubium, and Rupes Recta (the “Straight Wall”) flanks its eastern edge.

Mare Cognitum, the “Sea That Has Become Known”

Mare Cognitum lies between Mare Nubium and Oceanus Procellarum. It was named in 1964 after the Ranger 7 probe took the first U.S. close-up pictures of the Moon’s surface prior to crashing there.

Mare Insularum is north of Mare Cognitum. Its current name was bestowed upon it in 1976 by lunar geologist Don Wilhelms (1930-). The crater Kepler on its western edge separates Mare Insularum from Oceanus Procellarum. The crater Copernicus is on the northeast side of its western lobe.

Mare Vaporum is the mare closest to the center of the Moon’s nearside. The bright crater Manilius lies towards its northeastern edge and the volcanic crater Hyginus and its associated rille (Rima Hyginus) are immediately to its south.

Mare Imbrium was created 3.9 billion years ago when an asteroid some 150 miles across crashed into the Moon. This ancient feature is so large that it forms the right eye of the “Man in the Moon” we see when looking at a full or nearly full moon with our unaided eyes.

Mare Frigoris lies north and northeast of Mare Imbrium. The dark crater between them is Plato. It is the mare closest to the north pole of the Moon.

Now we begin our tour of the eastern hemisphere of the Moon’s nearside. Mare Serenitatis has the distinction of being the landing site of the last human mission to the Moon, Apollo 17, in 1972. It was also the landing site of the Soviet unmanned spacecraft Luna 21 just one month later.

Mare Tranquillitatis, the “Sea of Tranquility”

Mare Tranquillitatis is perhaps the most famous of the lunar maria, as it was there that humans first set foot on the surface of the Moon in 1969. The Apollo 11 landing site is located near its southwest corner.

Mare Nectaris lies south of Mare Tranquillitatis. This small, isolated, and nearly circular mare sports a prominent crater, Theophilus, at its northwest corner.

Mare Fecunditatis, the “Sea of Fertility”

East of Mare Nectaris lies Mare Fecunditatis. Superposed upon Mare Fecunditatis is the striking crater pair Messier and Messier A with two prominent rays evocative of a comet’s tail. Named after the famous French comet hunter Charles Messier (1730-1817), these craters and their associated rays were formed from a grazing impact from the east.

Mare Crisium is a round and isolated mare that makes it easy to remember why it is called the “Sea of Crises”. The Soviet Luna 24 unmanned sample return mission landed there in 1976. The six ounces of lunar materials it brought back to Earth are the last lunar samples scientists have received.

Mare Anguis lies just northeast of Mare Crisium and is called the “Serpent Sea” for its serpentine shape rather than the more fanciful name “Sea of Serpents” referred to by some science fiction authors.

Mare Undarum lies southeast of Mare Crisium. Its uneven texture and lack of uniform smoothness appears to justify its name as “the sea of waves”.

Mare Spumans lies south of Mare Undarum and east of Mare Fecunditatis. The bright crater Petit on the western side of this tiny mare evinces a bit of foam on “the foaming sea”.

Mare Australe hugs the southeastern limb of the lunar nearside. Though obliquely viewed from Earth and wrapping around to the lunar farside, favorable libration makes it visible in its entirety on occasion.

Mare Smythii on the eastern limb of the Moon is one of two lunar maria named after people. The lucky honoree is English hydrographer and astronomer William Henry Smyth (1788-1865). The lunar equator passes through Mare Smythii.

Mare Marginis lies east of Mare Crisium, right along the lunar limb. The crater Goddard on the northeast side of Mare Marginis exhibits bright deposits on its northeastern side. This crater and its associated deposits can only be seen from Earth during favorable librations.

Mare Humboldtianum, the “Sea of Alexander von Humboldt”

Mare Humboldtianum lies along the northeastern limb of the Moon and is the other lunar mare named after a person. The German astronomer Johann Heinrich von Mädler (1794-1874) named this feature after German geographer and explorer Alexander von Humboldt (1769-1859).

This completes our tour of the 21 maria on the nearside of the Moon.

References

António Cidadão’s Home-Page of Lunar and Planetary Observation and CCD Imaging, Moon-“Light” Atlas. Retrieved 22 April 2020.
http://www.astrosurf.com/cidadao/moonlight_mare_oceanus.htm

Ewen A. Whitaker, Mapping and Naming the Moon: A History of Lunar Cartography and Nomenclature (Cambridge University Press, 2003).

Shadows Cast by Starlight

Henry Norris Russell (1877-1957) received his Ph.D. at Princeton in 1899 at just 21 years of age. Three years later—in 1902 when he was 24 years old and years before his discovery of the color-luminosity relationship now known as the Hertzsprung-Russell (H-R) diagram—Russell had an interesting article published in the journal Popular Astronomy that shows him already to be a meticulous and perspicacious observational astronomer. This article, completed 118 years ago this day, is reprinted below.

SHADOWS CAST BY STARLIGHT.

HENRY NORRIS RUSSELL.

FOR POPULAR ASTRONOMY.

It has long been known that Venus casts a distinct shadow; and the same thing has sometimes been observed in Jupiter’s case. More recently, it has been stated in the daily press* that shadows cast by Sirius have been seen at the Harvard Observatory in Jamaica, though it was then said that they could probably be seen only where the air is exceptionally clear.

The writer began to investigate this subject, quite independently, last November, and has found that the shadows cast by a number of the brighter fixed stars can be seen without difficulty under ordinary circumstances, provided proper precautions are taken to exclude extraneous light, and to secure the maximum sensitiveness of the observer’s eyes.

* Interview with Professor W.H. Pickering, New York Tribune, Jan. 18, 1902.

The most convenient method of observation is as follows: Choose a window from which the star is visible, while as little light as possible enters from terrestrial sources. Darken the room completely, with the exception of this window. Open the window, and screen down its aperture to an area of a square foot or less. Hold a large piece of white paper in the path of the star’s rays, as far from the opening as possible. The image of the opening will then appear on the paper.

It cannot, however, be well seen until the observer has spent at least ten minutes in the dark, (to rest his eyes from the glare of ordinary lights). The paper should be held within a foot or so of the eyes, as the faint patch of starlight is most easily visible when its apparent area is large. The shadow of any convenient object may now be made to fall on the screen, and may be observed. By holding the object near the window and noticing that its shadow is still sharp, the observer may convince himself that the light which casts the shadow really comes from the star.

By the method above described, the writer has succeeded in distinguishing shadows cast by the following stars, (which are here arranged in order of brightness):

	Mag.		Mag.
α Canis Majoris (Sirius)	– 1.4	ζ Orionis	1.9
α Bootis (Arcturus)	0.0	β Tauri	1.9
α Aurigae (Capella)	0.2	γ Geminorum	2.0
β Orionis (Rigel)	0.3	β Canis Majoris	2.0
α Canis Minoris (Procyon)	0.5	α Hydrae	2.0
α Orionis* (Betelgeuse)	0.8?	α Arietis	2.0
α Tauri (Aldebaran)	1.0	κ Orionis	2.2
β Geminorum (Pollux)	1.1	β Leonis	2.2
α Virginis (Spica)	1.2	γ Leonis	2.2
α Leonis (Regulus)	1.4	δ Orionis	2.4
ε Canis Majoris	1.5	η Canis Majoris	2.4
α Geminorum (Castor)	1.6	ζ Argus	2.5
ε Orionis	1.8	α Ceti	2.7
δ Canis Majoris	1.9	15 Argus	2.9
γ Orionis	1.9

* Variable

The groups of stars comprised in the Pleiades and the sword of Orion also cast perceptible shadows. With a wide open window the belt of Orion should be added to this class.

Most of the observations on which this list is based were made at Princeton on February 7th, and 8th, and March 6th, 1902. The first of these nights is recorded as not remarkably clear, the others as very clear. Whenever there was any doubt of the reality of an observed patch of starlight, it was located at least three times, and it was verified each time that the star was really visible from the spot where its light had been located. Many more stars might have been added to the 29 in the foregoing list, had not unfriendly street lamps confined the observations to less than half the sky.

As many of the stars observed were at a low altitude, it may be concluded that a star of the 3rd magnitude, if near the zenith, would cast a perceptible shadow.

In attempting to get a shadow from these faint stars, the opening of the window should be narrowed to a width of a few inches, so as to cut off as much as possible of the diffused light of the sky. Care should be taken not to look at the sky while observing, as it is bright enough to dazzle the eyes for some little time.

By observing these precautions, the writer has been able to detect shadows cast by Sirius, Arcturus and Capella on moonlight nights,—in the case of Sirius, even when the Moon shone into the room.

The actual brightness of the screen, even when illuminated by Sirius, is very small in comparison with that of the “dark” background of the sky, as seen by the naked eye. White paper reflects about 80 per cent of the incident light. From photometric considerations, a disk of this material 1° in apparent diameter, illuminated perpendicularly by Sirius, should send us about 1/16,000 as much light as the star.

But, according to Professor Newcomb’s determination*, an area of sky 1° in diameter, remote from the Milky Way, sends us 9/10 as much light as a 5th magnitude star, or about 1/400 of the light of Sirius. Hence the sky is about 40 times as bright, area for area, as the paper illuminated by Sirius. The illumination of the paper by a 1st magnitude star is about 1/400 as bright, and by a 3d magnitude star less than 1/2000 as bright, area for area, as the “dark” background of the sky.

* Astrophysical Journal, December 1901.

This faint light, as might be anticipated, shows no perceptible color. The light of the white stars β and γ Orionis and the red star α Orionis does not differ sensibly in quality; but the light of the red star appears much fainter than the star’s brightness, as directly seen, would lead one to anticipate. On the screen, the light of α Orionis is much fainter than that of β, and only a little brighter than that of γ, while by direct vision α is much nearer to β than to γ in brightness. As β is 1 ½ magnitudes brighter than γ, it appears that, as measured by the intensity of its light on a screen, α Orionis is at least half a magnitude, perhaps a whole magnitude, fainter than when compared with the neighboring white stars by direct vision.

Such a result might have been anticipated à priori, since, in the ease of such faint lights as are here dealt with, the eye is sensitive to the green part of the spectrum alone, and this is relatively brighter in the spectrum of a white star than of a red one.

A much more interesting example of the accordance of theoretical prediction with observation is afforded by another phenomenon discovered by the writer, which is not hard to observe.

A surface illuminated by a planet—Venus for example—appears uniformly and evenly bright, but in the case of a fixed star, there are marked variations in brightness, so that the screen appears covered with moving dark markings.

This was predicted many years ago by Professor Young, in discussing the twinkling of the stars. He says*: “If the light of a star were strong enough, a white surface illuminated by it would look like the sandy bottom of a shallow, rippling pool of water illuminated by sunlight, with light and dark mottlings which move with the ripples on the surface. So, as we look toward the star, and the mottlings due to the irregularities of the air move by us, we see the star alternately bright and faint; in other words, it twinkles.”

General Astronomy, page 538 (edition of 1898).

It would be difficult to give a better description of the observed phenomenon than the one contained in the first part of the above quotation. It need only be added that the dark markings are much more conspicuous than the bright ones. This agrees with the fact that a star more frequently seems to lose light while twinkling than to gain it.

Sirius is the only star whose light is bright enough to make these light and dark mottlings visible without great difficulty, though the writer has seen them in the light of Rigel and Procyon. With Sirius they have been seen every time the star’s light has been observed on a moonless night. They are much more conspicuous when the star is twinkling violently than on nights when the air is steady. In the latter case there are only faint irregular mottlings, whose motion produces a flickering effect. More usually there appear also ill-defined dark bands, two or three inches wide. These are never quite straight nor parallel but usually show a preference for one or two directions, sometimes dividing the screen into irregular polygons. On some nights they merely seem to oscillate, but on others they have a progressive motion, which may be at any angle with their own direction. The rate of motion is very variable, but is greatest on windy nights,—another evidence of the atmospheric origin of the bands.

The best nights for observing these bands occur when the stars are twinkling strongly, and there is not much wind. The directions given above for observing shadows should be somewhat modified in this case.

If the room is not at the same temperature as the outer air, the window should be kept closed, as otherwise most of what is seen will be due to the air-currents near it. It is also desirable to have an area of star-light at least a foot square to see the bands in, so that a good sized part of the window should be left clear.

If Sirius is unavailable, Arcturus and Vega are probably the best stars in whose light to attempt to see the bands.

PRINCETON, N. J., March 24, 1902.

Happy Birthday, AAAA!

The first meeting of the Ames Area Amateur Astronomers (AAAA) took place 40 years ago today: Saturday, June 2, 1979. Central Junior High Earth Science teacher Jack Troeger and Welch Junior High Earth Science Teacher Ron Bredeson held the first meeting in Jack’s classroom in the building that is now the Ames City Hall. This was a great start to a great astronomy club. Here’s to the next 40 years!

And, we just passed another important milestone in AAAA history. The grand opening of the original McFarland Park Observatory took place 35 years ago on Memorial Day, Monday, May 28, 1984. Back then, the pavement ended at the intersection of Dayton Rd. & County Road E-29, northeast of Ames, Iowa, and it was gravel the rest of the way.

The first McFarland Park Observatory with its second telescope, a 12.5-inch Newtonian & Cassegrain telescope. The first telescope was a 13.1-inch Coulter Odyssey Dobsonian.

Observatory manager Jim Doggett and AAAA president David Oesper inside the original McFarland Park Observatory. Lower right photo is Julie Oesper and Katie Dilks watching the spectacular aurora borealis display the evening of November 8, 1991.

The AAAA purchased a backyard-observatory silo-top dome from Glen Hankins in Nevada on Saturday, September 27, 1980, and then-Ranger (and later Story County Conservation Director) Steve Lekwa of McFarland Park was instrumental in allowing the AAAA to build its observatory at its present site at McFarland Park. The much-improved replacement roll-off-roof observatory, named after club members and benefactors Bertrand & Mary Adams, was completed in 2000. The only part of the original observatory structure that remains is the telescope pier!

Scintillating Stars But Not Planets

Aristotle (384 BC – 322 BC) may have been the first person to write that stars twinkle but planets don’t, though our understanding of twinkling has evolved since he explained that “The planets are near, so that the visual ray reaches them in its full vigour, but when it comes to the fixed stars it is quivering because of the distance and its excessive extension.”

John Stedman (1744-1797), a controversial and complicated figure to be sure, writes the following dialog between teacher and student in The Study of Astronomy, Adapted to the capacities of youth (1796):

PUPIL. How is the twinkling of the stars in a clear night accounted for?

TUTOR. It arises from the continual agitation of the air or atmosphere through which we view them; the particles of air being always in motion, will cause a twinkling in any distant luminous body, which shines with a strong light.

PUPIL. Then, I suppose, the planets not being luminous, is the reason why they do not twinkle.

TUTOR. Most certainly. The feeble light with which they shine is not sufficient to cause such an appearance.

Still not quite right, but closer to our current understanding. Our modern term for “twinkling” is atmospheric scintillation, which is changes in a star’s brightness caused by curved wavefronts focusing or defocusing starlight.

Scintillation is caused by refractive index variations (due to differences in pressure, temperature, and humidity) of “pockets” of air passing in front of the light path between star and observer at a typical height of about 5 miles. These pockets are typically about 3 inches across, so from the naked eye observer’s standpoint, they subtend an angle of about 2 arcseconds.

The largest angular diameters of stars are on the order of 50 milliarcseconds¹ (R Doradus, Betelgeuse, and Mira), and only seventeen stars have an an angular diameter larger than 1 milliarcsecond. So, it is easy to see how cells of air on the order of 2 arcseconds across moving across the light path could cause the stars to flicker and flash as seen with the unaided eye.

The five planets that are easily visible to the unaided eye (Mercury, Venus, Mars, Jupiter, and Saturn) have angular diameters that range from 3.5 arcseconds (Mars, at its most distant) up to 66 arcseconds (Venus, at its closest). Since the disk of a planet subtends multiple air cells, the different refractive indexes tend to cancel each other out, and the planet shines with a steady light.

From my own experience watching meteors many nights with my friend Paul Martsching, our reclining lawn chairs just a few feet apart, I have sometimes seen a principal star briefly brighten by two magnitudes or more, with Paul seeing no change in the star’s brightness, and vice versa.

Stedman’s dialogue next turns to the distances to the nearest stars.

PUPIL. Have the stars then light in themselves?

TUTOR. They undoubtedly shine with their own native light, or we should not see even the nearest of them: the distance being so immensely great, that if a cannon-ball were to travel from it to the sun, with the same velocity with which it left the cannon, it would be more than 1 million, 868 thousand years, before it reached it.

He adds a footnote:

The distance of Syrius is 18,717,442,690,526 miles. A cannon-ball going at the rate of 1143 miles an hour, would only reach the sun in about 1,868,307 years, 88 days.

Where Stedman comes up with the velocity of a cannon-ball is unclear, but the Earth’s rotational speed at the equator is 1,040 mph, close to Stedman’s cannon-ball velocity of 1,143 mph. He states the distance to the brightest star Sirius—probably then thought to be the nearest star—is 18,717,442,690,526 miles or 3.18 light years, a bit short of the actual value of 8.60 light years. The first measurements of stellar parallax lie 42 years in the future when Stedman’s book was published.

¹ 1 milliarcsecond (1 mas) = 0.001 arcsecond

References
Aristotle, De Caelo, Book 2, chap.8, par. 290a, 18
Crumey, A., 2014, MNRAS, 442, 2600
Dravins, D., Lindegren, L., Mezey, E., Young, A. T., 1997a, PASP, 109, 173
Ellison, M. A., & Seddon, H., 1952, MNRAS, 112, 73
Stedman, J., 1796, The Study of Astronomy, Adapted to the capacities of youth

Rhapsody in Blue

American composer George Gershwin left us much too soon at the young age of 38. He died of a brain tumor in 1937, and eight years after his death a somewhat fictionalized movie about his life was released in 1945, Rhapsody in Blue.

One remarkable aspect of this movie is a number of people who knew Gershwin were in the movie as themselves: Oscar Levant, Paul Whiteman (who premiered Rhapsody in Blue), Hazel Scott, Anne Brown, Al Jolson, George White, and Elsa Maxwell. It is a love letter to this remarkable composer and musician.

Robert Alda (father of Alan Alda) turns in a great performance as George Gershwin, as does Joan Leslie as his fictionalized love interest Julie Adams.

Robert Alda as George Gershwin and Joan Leslie as Julie Adams in **Rhapsody in Blue** (1945)

Strong performances were also turned in by Morris Carnovsky as George Gershwin’s father, Albert Bassermann as his fictionalized teacher Professor Franck (perhaps patterned in part after both Charles Hambitzer and Rubin Goldmark), and Herbert Rudley as Ira Gershwin.

And then there’s the wonderful music of George Gershwin throughout the film, including much of An American in Paris, a personal favorite of mine. I’ll bet you’ll hear familiar songs that you didn’t even know were written by Gershwin!

I loved this movie. Unfortunately, it is not available through either Netflix or Amazon streaming, but you can purchase a DVD through several sources.

If you don’t know much about George Gershwin, this movie is a good starting point. After you watch it, I guarantee you’ll want to learn more about the real George Gershwin and his music. Enjoy!