Friday, October 30, 2015

Lyra - small triangle ε Lyr and ζ Lyr

Lyra, small triangle
Cropped from "Lyra constellation detail long exposure" by Scott Roy Atwood - Own work.
Licensed under CC BY-SA 3.0 via Commons

The brightest star in Lyra, Vega, forms a small triangle with Epsilon and Zeta Lyrae.

Zeta Lyr 
This is a wide binary star consisting of an F-type subgiant and an Am star.

F-type subgiants are subgiant (luminosity class IV) stars of spectral type F.  (A subgiant is a star that is slightly brighter than a normal main-sequence (dwarf) star of the same spectral class, but not as bright as true giant stars.)

The Am star has an additional close companion, bringing the total number of stars in the system to three.
An Am star or metallic-line star is a type of chemically peculiar star of spectral type A whose spectrum has strong and often variable absorption lines of metals such as zinc, strontium, zirconium, and barium, and deficiencies of others, such as calcium and scandium.

These abnormalities are due to some elements which absorb more light being pushed towards the surface, while others sink under the force of gravity. This effect takes place only if the star has low rotational velocity.

Normally, A-type stars rotate quickly. Most Am stars form part of a binary system in which the rotation of the stars has been slowed by tidal braking. The best-known metallic-line star is Sirius (α Canis Majoris).

Epsilon Lyr 

This "Double Double" is a wide binary. Both components are themselves close binaries which can be seen with telescopes to consist of A- and F-type stars, and a faint star was recently found to orbit component C as well, for a total of five stars.
If components in binary star systems are close enough they can gravitationally distort their mutual outer stellar atmospheres. In some cases, these close binary systems can exchange mass, which may bring their evolution to stages that single stars cannot attain. Examples of binaries are Sirius and Cygnus X-1 (Cygnus X-1 being a well known black hole).
An A-type main-sequence star (A V) or A dwarf star is a main-sequence, hydrogen-burning star of spectral type A and luminosity class V.
  • These stars have spectra which are defined by strong hydrogen Balmer absorption lines.  
  • They have masses from 1.4 to 2.1 times the mass of the Sun and surface temperatures between 7600 and 11 500  K. 
Bright and nearby examples are Altair (A7 V), Sirius A (A1 V), and Vega (A0 V)

An F-type main-sequence star (F V) is a main-sequence, hydrogen-fusing star of spectral type F and luminosity class V.
  • These stars have from 1.0 to 1.4 times the mass of the Sun 
  • and surface temperatures between 6,000 and 7,600 K,  This temperature range gives the F-type stars a yellow-white hue
Famous examples include Procyon A Canis Minoris and Gamma Virginis A and B.

By studying the little triangle of Lyra we learn about star classification which is a fundamental branch of Astronomy. In the case of the triangle focus here is on the main-sequence, mass, surface temperature, luminosity, absorption lines, hue of the star and terminology.

Both Zeta and Epsilon Lyrae introduce the important phenomenon of binary stars which have been such a rich source of information about stellar dynamics, physics and other aspects of star life.

Wikipedia quotes are here for the reader's convenience. By linking to the articles much more can be learned about the subjects. (Note that I have slightly edited the quotes for the flow of the text being careful not to change the original content in any way.)

Thursday, October 29, 2015

Lyra - starlight and Vega

Summer triangle created in Stellarium
Image Astro Bob

Twinkle, twinkle little star
How I wonder what you are!

In many cultures, ancient and new, Lyra is seen as a musical instrument among the many constellations on the night sky. For astronomers it is also an accurately mapped chunk of real estate on the sky with 17-sided polygonal border. As such it is a helpful quick reference to the approximate location of a given heavenly object. The accurate location is defined with incredibly exact instruments and methods allowing the pointing of research instruments to the tiniest spots in the night sky, some visible, some invisible to naked eye. This accuracy deservedly raises Astronomy to the top league among natural sciences and to one of the most expensive among them.

Astronomers use sophisticated mathematical calculations to analyze captured visible star light, other bandwidths of electro-magnetic and other radiation reaching Earth from the cosmos. In fact, all our knowledge about the Universe is based on these studies and analyses of star light.

Astronomers had to rely on observations by naked eye until the invention of optics in late 16th century Netherlands. Telescopes have since then totally revolutionized the study of star light and are getting more powerful by the year.

Newtonian prism and spectrum analysis added later a significant aspect to studies of star light. The tints of color appearing to the naked eye have been expanded by these means to a glorious rainbow of colors and shades reaching us from near and distant stars.

Standard spectral classification

Data from J. C. Evans, George Mason University
Spectral ClassIntrinsic ColorTemperature (K)Prominent Absorption Lines
OBlue41,000He+, O++, N++, Si++, He, H
BBlue31,000He, H, O+, C+, N+, Si+
ABlue-white9,500H(strongest), Ca+, Mg+, Fe+
FWhite7,240H(weaker), Ca+, ionized metals
GYellow-white5,920H(weaker), Ca+, ionized & neutral metal
KOrange5,300Ca+(strongest), neutral metals strong, H(weak)
MRed3,850Strong neutral atoms, TiO
Table from Hyperphysics Georgia State University

Basic description of a star usually includes
  • Star type in main-sequence or other type
  • Location in celestial equator sphere given by Right ascension and Declination or Azimuth/Altitude
  • Magnitude defined from absolute and apparent brightness
  • Color index
  • Spectral type
  • Distance from Sun
  • Parallax, apparent shift of position against the background of distant objects

Universe is vast, to say the least!  One way to learn to know it better is to study the variety of stars in a given constellation only. As first step, below is listing of astronomical information about Vega, the brightest star in Lyra and the fifth brightest star on Earth's sky. The listing is followed by asummary of its special characteristics.

Bayer  (B): α
Flamsteed  (F): 3
Henry Draper Catalogue  (HD): 172167
Hipparcos Catalogue  (HIP): 91262
Right ascension (RA): 18h 36m 56.19s
Declination (Dec): +38° 46′ 58.8″

Absolute: 0.58
Visible: 0.03

Distance from Sun
25 light years

Spectral class 

Special aspects
Vega has been extensively studied by astronomers, leading it to be termed "arguably the next most important star in the sky after the Sun."

Vega was the northern pole star around 12,000 BC and will be so again around the year 13,727 when the declination will be +86°14'.

Vega was the first star other than the Sun to be photographed and the first to have its spectrum recorded.

It was one of the first stars whose distance was estimated through parallax measurements.

Vega has served as the baseline for calibrating the photometric brightness scale, and was one of the stars used to define the mean values for the UBV photometric system.

Vega is only about a tenth of the age of the Sun, but since it is 2.1 times as massive its expected lifetime is also one tenth of that of the Sun; both stars are at present approaching the midpoint of their life expectancies.

Vega has an unusually low abundance of the elements with a higher atomic number than that of helium.

Vega is also a suspected variable star that may vary slightly in magnitude in a periodic manner.  It is rotating rapidly with a velocity of 274 km/s at the equator. This is causing the equator to bulge outward because of centrifugal effects, and, as a result, there is a variation of temperature across the star's photosphere that reaches a maximum at the poles. From Earth, Vega is being observed from the direction of one of these poles.

Based on an observed excess emission of infrared radiation, Vega appears to have a circumstellar disk of dust. This dust is likely to be the result of collisions between objects in an orbiting debris disk, which is analogous to the Kuiper belt in the Solar System. Stars that display an infrared excess because of dust emission are termed Vega-like stars.

Wednesday, October 28, 2015

Lyra - characteristics and cultural Astronomy

"LyraCC" by Till Credner - Own work: Licensed under CC BY-SA 3.0 via Commons
Lyra is a small constellation but remarkable because of Vega, the second brightest star on Northern hemisphere and fifth brightest among all the stars visible from Earth. It is preceded only by Sirius, Canopus, Alpha Centauri and Arcturus.

Characteristics of the constellation
Lyra is bordered by Vulpecula to the south, Hercules to the east, Draco to the north, and Cygnus to the west.

Covering 286.5 square degrees, it ranks 52nd of the 88 modern constellations in size.

It appears prominently in the northern sky during the Northern Hemisphere's summer, and the whole constellation is visible for at least part of the year to observers north of latitude 42° S.

Its main asterism consists of six stars, and 73 stars in total are brighter than magnitude 6.5.

The constellation's boundaries, as set by Eugène Delporte in 1930, are defined by a 17-sided polygon. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 08h 14m and 19h 28m, while the declination coordinates are between +25.66° and +47.71°.

The International Astronomical Union (IAU) adopted the three-letter abbreviation "Lyr" for the constellation in 1922.

Cultural Astronomy

Constellations are products of human mental processes combining stars into each other by lines and thus seeing in them familiar objects, animals or mythological figures. As Lyra is not in the zodiac it had no astrological significance. It was simply part of ancient mental mapping of the night sky.

Ptolemy of Alexandria (c. AD 100 – c. 170) includes Lyra in his list of 48 constellations. He uses the name familiar to us (Greek λύρα). The constellation is visible during great part of the year on Greek night sky. It is  marked by the remarkable star we call Vega. Ancient Greeks associated the shape of the constellation with an instrument well before Ptolemy's times and told that the muses had set Orpheus' lyre up on the sky after the death of the tragic musician.

Arab astronomers made a kind of cocktail of themes seeing in the constellation a vulture or an eagle carrying a lyre. What was the symbolism in this?

Persian poet Hafez (حافظ Hāfiz; 1325/26–1389/90) called the constellation The Lyre of Zurah translated as kithara. (see Constellation of Words).

"Leipoa ocellata -Ongerup, Western Australia, Australia-8" by butupa - via Commons
Boorong people in Victoria, Australia, see in the shape of Lyra the Malleefowl bird.

Inca herders worshiped the constellation as Urcuchillay considered a sacred multicolored lama.

Tuesday, October 20, 2015

Virtual Lunar Atlas

Virtual Lunar Atlas home
From VLA homepage
My personal studies of the Moon just got a giant leap forward when I found and downloaded Virtual Lunar Atlas. It is a wonderful software package offered for free (or support it by buying the DVD) and recommended by very serious players such as European Space Agency ESA and the French Ministry of National Education.

This software, realized by Patrick Chevalley and Christian Legrand can visualize the Moon aspect for every date and hour and pilot computerized telescopes on the Moon surface. It permits also to study lunar formations with unique database of more than 9000 entries and a more than 7000 pictures library compiled by Christian Legrand.

It's conceived to be easily usable “in the field” according to an observing session needs, but also to study “at home” the Moon and its surface. It's interfaced with "Sky charts" Patrick Chevalley's freeware. This set is certainly now one of the most complete astronomy softwares set released.

This software has been conceived according to the needs of Moon observers, but also as a powerful tool for people interested personally or professionally by selenography.
Virtual Lunar Atlas homepage

Thank you so much to the authors and all the contributors to this shining example of possibilities offered to Astronomy by modern software and Web developments. It certainly deserves to be more widely known.

Monday, October 19, 2015

Cultural Astronomy: Southern Cross

The constellation is seen as a cross by the colonialists arriving to southern hemisphere and Pacific ocean from the Christian West. The cross shape is so deep in our cultures and psyche that seeing the four bright star in the way depicted in the schema above is quite natural. But in fact, it forcibly pairs the opposing four stars to this geometric shape.

In many cultures in the southern hemisphere people do not pair the stars in this manner but rather follow the natural outline of the constellation. This shape is then associated with some animal or object important in their culture. 

The following paragraphs are from Wikipedia which also includes references to the studies where these identifications have been discussed. (there are many references to Staal, Frits. 1988.Universals: Studies in Indian logic and linguistics. Chicago: University of Chicago Press.)

I have added to the wiki text some images and links to emphasize the great variety in the way how various non-western people have perceived the Crux, the Coalsack and the stars nearby.

In Australian Aboriginal astronomy, Crux and the Coalsack mark the head of the 'Emu in the Sky' in several Aboriginal cultures, while Crux itself is said to be a possum sitting in a tree and a representation of the sky deity Mirrabooka. (The dark Coalsack nebula is in the area of the constellation).

image How stuff works

Torres Strait Islanders in modern-day Australia saw Gamma Centauri as the handle and the four stars as the trident of Tagai's Fishing Spear.

The constellation of Tagai, on which Torres Strait Islander culture is based.
Image credit: Nonie Sharp, 'Stars of Tagai: The Torres Strait Islanders',
based upon a watercolour by Lieut.G.Tobin, Mitchell Library,
and drawings of the Tagai Constellation by Gizu and Mariget of Mabuiag
Australian Indigenous Astronomy

The Aranda people of central Australia saw the four Cross stars as the talon of an eagle and Gamma Centauri as its leg.
Drawing Colorign Sun

Various peoples in the East Indies and Brazil viewed the four main stars as the body of a ray. In both Indonesia and Malaysia, it is known as Bintang Pari and Buruj Pari respectively ("ray stars").

"Eagle ray jb". Licensed under Public Domain via Commons

The Javanese people of Indonesia called this constellation Gubug pèncèng ("raking hut") or lumbung ("the granary"), because the shape of the constellation was like a raking hut.

In the Pacific region granaries had also great religious importance.

The Māori name for the Southern Cross is Te Punga ("the anchor"). It is thought of as the anchor of Tama-rereti's waka (the Milky Way), while the Pointers are its rope. (Pointers are the two bright stars near the Crux helping to find it.)
Traditional Melanese anchor

In Tonga it is known as Toloa ("duck"); it is depicted as a duck flying south, with one of his wings (δ Crucis) wounded because Ongo tangata ("two men", α and β Centauri) threw a stone at it. The Coalsack is known as Humu (the "triggerfish"), because of its shape.

Image Wikipedia Commons

In Samoa the constellation is called Sumu ("triggerfish") because of its rhomboid shape, while α and β Centauri are called Luatagata (Two Men), just as they are in Tonga.

"4987 aquaimages". Licensed under CC BY-SA 2.5 via Commons

The peoples of the Solomon Islands saw several figures in the Southern Cross. These included a knee protector and a net used to catch Palolo worms. (Eaten there as food)

"A good catch of palolo nps gov" by U.S. Department of the Interior National Park Service
via Commons

Neighboring peoples in the Marshall Islands saw these stars as a fish.

In Mapudungun, the language of Patagonian Mapuches, the name of the Southern Cross is Melipal, which means "four stars".

In Quechua, the language of the Inca civilization, Crux is known as "Chakana", which means literally "stair" (chaka, bridge, link; hanan, high, above), but carries a deep symbolism within Quechua mysticism. Acrux and Mimosa make up one foot of the Great Rhea, a constellation encompassing Centaurus and Circinus along with the two bright stars.

The Great Rhea was a constellation of the Bororo people of Brazil.

"Rhea americana qtl2" by Quartl - Own work.
Licensed under CC BY-SA 3.0 via Commons

The Bakairi people of Brazil had a sprawling constellation representing a bird snare. It included the bright stars of Crux, the southern part of Centaurus, Circinus, at least one star in Lupus, the bright stars of Musca, Beta and Delta Chamaeleonis, Volans, and Mensa.

The Kalapalo people of Mato Grosso state in Brazil saw the stars of Crux as Aganagi angry bees having emerged from the Coalsack, which they saw as the beehive.

Natural beehive
Image Naughty Boy

The Mocoví people of Argentina also saw a rhea including the stars of Crux. Their rhea is attacked by two dogs, represented by bright stars in Centaurus and Circinus. The dogs' heads are marked by Alpha and Beta Centauri. The rhea's body is marked by the four main stars of Crux, while its head is Gamma Centauri and its feet are the bright stars of Musca.

Among Tuaregs, (North Africa) the four most visible stars of Crux are considered iggaren, i.e. four Maerua crassifolia trees.

A large Maerua crassifolia tree
Image King Saud University
The Tswana people of Botswana saw the constellation as Dithutlwa, two giraffes - Acrux and Mimosa forming a male, and Gacrux and Delta Crucis forming the female.

Two Rotschild giraffes at Woburn Safari Park, United Kingdom
Image Wikimedia

Southern Cross, the Crux

Schematic representation of Southern Cross, the Curx
image Globe at Night
What would Astrotheology be without studying the famous cross visible in southern skies?

Constellation Crux is visible only in the southern hemisphere and is defined by four stars, Alpha, Beta, Gamma and Delta Crucis shown clockwise in the schema starting from the brightest star at the bottom of the cross. Under optimal conditions also Epsilon Crucis is visible to the naked eye.

Also known as Acrux, Alpha Crucis is a triple star 321 light-years from Earth. Blue-tinged and magnitude 0.8 to the unaided eye, it has two close components of magnitude 1.3 and 1.8, as well as a wide component of magnitude 5. The two close components are divisible in a small amateur telescope and the wide component is divisible in a pair of binoculars.

Beta Crucis, called Mimosa, is a blue-hued giant of magnitude 1.3, 353 light-years from Earth. It is a Beta Cephei-type Cepheid variable with a variation of less than 0.1 magnitudes.

Gamma Crucis, called Gacrux, is an optical double star. The primary is a red-hued giant star of magnitude 1.6, 88 light-years from Earth. The secondary is of magnitude 6.5, 264 light-years from Earth.

Delta Crucis is a blue-white hued star of magnitude 2.8, 364 light-years from Earth. It is the dimmest of the Southern Cross stars. Like Beta it is a Beta Cepheid.

Epsilon Crucis is an orange-hued giant star of magnitude 3.6, 228 light-years from Earth.

Iota Crucis is a binary star 125 light-years from Earth. The primary is an orange-hued giant of magnitude 4.6 and the secondary is of magnitude 9.5.

Mu Crucis is a double star where the unrelated components are about 370 light-years from Earth. The primary is a blue-white hued star of magnitude 4.0 and the secondary is a blue-white hued star of magnitude 5.1. Mu Crucis is divisible in small amateur telescopes or large binoculars.

Aid in finding the southern celestial pole 
An imaginary line drawn through Gacrux and Acrux points towards southern celestial pole. For navigators the constellation has had similar role to Polaris in the northern sky which faithfully points towards the northern celestial pole.

It has been an important aid for finding south ever since the Middle Ages when Portuguese and Spanish sailors learned to know the constellation.

National symbol
Several nations have included the Crux in their flags

New Zealand
Papua New Guinea
The Southern Cross appears also in Brazilian passports issued from 2015 on.

Saturday, October 17, 2015

Moon: Atlas

Lunar Orbiter 4 image of Atlas
"Atlas crater 4079 h2 4079 h3" by James Stuby based on NASA image via Commons
Atlas Crater
Atlas is a prominent lunar impact crater that is located in the northeast part of the Moon, to the southeast of Mare Frigoris. Just to the west is the slightly smaller but still prominent crater Hercules. Northeast of Atlas is the large Endymion.

The inner wall of Atlas is multiply terraced and the edge slumped, forming a sharp-edged lip. This is a floor-fractured crater with a rough and hilly interior that has a lighter albedo than the surroundings. Floor-fractures are usually created as a result of volcanic modifications.

There are two dark patches along the inner edge of the walls; one along the north edge and another besides the southeast edges. A system of slender clefts named the Rimae Atlas crosses the crater floor, and were created by volcanism. Along the north and northeastern inner sides are a handful of dark-halo craters, most likely due to eruptions. Around the midpoint is a cluster of low central hills arranged in a circular formation.

Sculpture of Atlas, Praza do Toural, Santiago de Compostela.
"Atlas Santiago Toural GFDL" by Luis Miguel Bugallo Sánchez
Own work. Licensed under CC BY-SA 3.0 via Commons
In Greek mythology, Atlas (Ancient Greek: Ἄτλας) was the Titan who held up the sky. Although associated with various places, he became commonly identified with the Atlas Mountains in northwest Africa (Modern-day Morocco, Algeria and Tunisia). Atlas was the son of the Titan Iapetus and the Oceanid Asia or Clymene. According to the ancient Greek poet Hesiod Atlas stood at the ends of the earth towards the west.

In contexts where a Titan and a Titaness are assigned each of the seven planetary powers, Atlas is paired with Phoebe and governs the moon. Hyginus emphasises the primordial nature of Atlas by making him the son of Aether and Gaia.

The first part of the term Atlantic Ocean refers to "Sea of Atlas", the term Atlantis refers to "island of Atlas".
Geocentric world view gets concrete aspect at Santiago de Compostela where the statue in the above image stands. The shore of Atlantic Ocean was for the ancients the edge of the world beyond which there was the great unknown with its monsters. Some of Christopher Columbus' sailors still had deep fear of them. The ancients came there on foot perhaps already in the Prehistoric period to see how the Sun sets in West. The ancient path from Europe to this part of the Iberian Peninsula later became the route of the famous pilgrimage to the tomb of St. Jacob, one of the twelve Apostles of Jesus (Santiago, Sant Jacob). The traditions about St Jacob have here a strong local coloring. For example, the ubiquitous shell symbol now associated with him probably has a history hundreds if not thousands of years before the Saint.

The figure of Atlas is a reminder that while exceptionally gifted classical Greek scientists pondered the laws of nature in the solar system, visible planets and Earth using observations, logic and mathematics, the masses shared a rich mythological world about Earth and Sky with quite imaginary but essentially common sense explanations to phenomena. How does the sky stay up? Well, obviously someone pretty strong is holding it ...

Excerpts from Wiki texts have been incorporated into the blog as kinds of abstracts for reader's convenience. By clicking the links much more can be learned about these subjects.

Moon: Plato

Plato crater viewed from the Earth
"Plato Crater" by Velasoraptor
This is a Registax output file of a video shot using Sky-watcher 6 inch Dobsonian Telescope,
Orion 3x Barlow Lens & Canon EOS 550D DSLR camera
Licensed under CC BY-SA 3.0 via Commons
Plato Crater
Plato is the lava-filled remains of a lunar impact crater on the Moon. It is located on the northeastern shore of the Mare Imbrium, at the western extremity of the Montes Alpes mountain range. In the mare to the south are several rises collectively named the Montes Teneriffe. To the north lies the wide stretch of the Mare Frigoris. East of the crater, among the Montes Alpes, are several rilles collectively named the Rimae Plato.

The age of Plato is about 3.84 billion years, only slightly younger than the Mare Imbrium to the south. The rim is irregular with 2-km-tall jagged peaks that project prominent shadows across the crater floor when the Sun is at a low angle. Sections of the inner wall display signs of past slumping, most notably a large triangular slide along the western side. The rim of Plato is circular, but from the Earth it appears oval due to foreshortening.

The flat floor of Plato has a relatively low albedo, making it appear dark in comparison to the surrounding rugged terrain. The floor is free of significant impact craters and lacks a central peak. However there are a few small craterlets scattered across the floor.

Plato has developed a reputation for transient lunar phenomena, including flashes of light, unusual colour patterns, and areas of hazy visibility. These anomalies are likely a result of seeing conditions, combined with the effects of different illumination angles of the Sun.

Plato (Greek: Πλάτων Plátōn; 428/427 or 424/423 – 348/347 BC) was a philosopher and mathematician in Classical Greece, and the founder of the Academy in Athens, the first institution of higher learning in the Western world. He is widely considered the most pivotal figure in the development of philosophy, especially the Western tradition. Unlike nearly all of his philosophical contemporaries, Plato's entire œuvre is believed to have survived intact for over 2,400 years.

Plato and Aristotle are towering figures among classical Greek thinkers and have had deep impact on humanity. However, like Aristotle, also Plato seems to have written very little if anything specifically about Astronomy.

Excerpts from Wiki texts have been incorporated into the blog as kinds of abstracts for reader's convenience. By clicking the links much more can be learned about these subjects.

Moon: Aristoteles

Location of Aristoteles as photographed at the McDonald Observatory
"Aristoteles Crater" by EricandHolli (talk) (Uploads) - Own work. Licensed under CC BY-SA 3.0 via Wikipedia

Aristoteles Crater 
Aristoteles is a lunar impact crater that lies near the southern edge of the Mare Frigorisand to the east of the Montes Alpes mountain range. To the south of Aristoteles lies the slightly smaller crater Eudoxus and these two form a distinctive pair for a telescope observer. An arc of mountains between these craters bends to the west before joining the walls. The smaller crater Mitchell is directly attached to the eastern rim of Aristoteles. To the west is the low, flooded feature Egede.

Aristotle Greek: Ἀριστοτέλης  Aristotélēs; 384 – 322 BC) was a Greek philosopher and scientist born in the Macedonian city of Stagira, Chalkidice, on the northern periphery of Classical Greece. His father, Nicomachus, died when Aristotle was a child, whereafter Proxenus of Atarneus became his guardian.

At eighteen, he joined Plato's Academy in Athens and remained there until the age of thirty-seven (c. 347 BC). His writings cover many subjects – including physics, biology, zoology, metaphysics, logic, ethics, aesthetics, poetry, theater, music, rhetoric, linguistics, politics and government – and constitute the first comprehensive system of Western philosophy. Shortly after Plato died, Aristotle left Athens and, at the request of Philip of Macedon, tutored Alexander the Great starting from 343 BC.

According to the Encyclopædia Britannica, "Aristotle was the first genuine scientist in history ... [and] every scientist is in his debt."

If I am not mistaken this world famous Greek scientist did not contribute particularly much to Astronomy in his vast body of writings on various subjects.

Excerpts from Wiki texts have been incorporated into the blog as kinds of abstracts for reader's convenience. By clicking the links much more can be learned about these subjects.

Moon craters with Greek names

The person who chose to name the selenographical feature after astronomers was the Jesuit mathematician, astronomer and physicist Giovanni Battista Riccioli who was born 17th April 1598.
Renaissance Mathematics

The Greek names given to Moon craters by Giovanni Riccioli offer us also today a nice way to memorize the features and give a compact introduction to the history of Greek Astronomy. Some of these are studied in the blogs referred below by the name of the crater. Wikipedia quotes are used to describe the crater and there are compact discussions of the astronomic contributions of the named persons. The Moon is an interesting way to learn to know better the exceptional achievements of ancient scholars who were able just by observation, logical reasoning and mathematical thinking to figure out secrets of the universe without help of telescopes.

While Byzantine and Latin Christian world was not enthusiastic about pagan Greek science and many of the works were forgotten, major works were translated into Arabic and studied by Islamic scholars. When East and West met rather violently during the Crusader period West learned from East to appreciate the wisdom and learning of ancient Greeks.

An exception is, of course, Ptolemy's Almagest (known by the Arabic form of the name) that was universally used by all in Christian and Islamic worlds guiding navigatros who relied on the movements of Sun, Moon, the five visible planets and stars on the sky.

In addition to the names of Greek and one Roman scholars the list contains two mythological characters, Endymion, which I included because of the beauty of the legend associated with Moon goddess Selene and Atlas, the Titan who according to Greek mythology holds up the sky but not particularly associated with any heavenly bodies on the sky.










Menelaus (Roman)







Friday, October 16, 2015

Moon: Plinius

Oblique view from Apollo 17 facing south, and showing both Plinius crater and Plinius Rilles
"Plinius crater AS17-M-1660" by James Stuby based on NASA image via Commons

Plinius Crater
Plinius is a prominent lunar impact crater on the border between Mare Serenitatis to the north and Mare Tranquilitatis to the south. South-southeast of Plinius is the crater Ross, and to the northeast is Dawes

Just to the north is a system of rilles named the Rimae Plinius. At the northwest edge of the rille is the Promontorium Archeruia, a cape off the western rim that encloses the Mare Serenitatis.

The sharp rim of Plinius is slightly oval in form, with a terraced inner wall, and an irregular outer rampart. It lacks a visible ray system. The crater floor is hilly, and in the middle is an irregular central peak that has the appearance of a double crater formation under certain angles of illumination. 

There is a cleft feature attached to the northern side of the peak. The eastern half of the floor is much more smooth and level than the hummocky west, and this section forms a crescent shape about the central peak.

Pliny the Elder
Gaius Plinius Secundus (AD 23 – August 25, AD 79), better known as Pliny the Elder, was a Roman author, naturalist, and natural philosopher, as well as naval and army commander of the early Roman Empire and personal friend of the emperor Vespasian.

Spending most of his spare time studying, writing or investigating natural and geographic phenomena in the field, he wrote an encyclopedic work, Naturalis Historia, which became a model for all other encyclopedias. 

The Naturalis Historia is one of the largest single works to have survived from the Roman Empire to the modern day and purports to cover the entire field of ancient knowledge, based on the best authorities available to Pliny. He claims to be the only Roman ever to have undertaken such a work. It encompasses the fields of botany, zoology, astronomy, geology and mineralogy as well as the exploitation of those resources. It remains a standard work for the Roman period and the advances in technology and understanding of natural phenomena at the time.

Pliny the Elder died on August 25, AD 79, whilst attempting to rescue Pomponianus (a friend of Pliny's) and his family from the eruption of Mount Vesuvius that had just destroyed the cities of Pompeii and Herculaneum.

Excerpts from Wiki texts have been incorporated into the blog as kinds of abstracts for reader's convenience. By clicking the links much more can be learned about these subjects.


Moon: Archimedes

"Archimedes crater AS15-M-1542" by NASA  via Commons
Apollo 15
Archimedes Crater
Archimedes is a large lunar impact crater on the eastern edges of the Mare Imbrium. The diameter of Archimedes is the largest of any crater on the Mare Imbrium. The rim has a significant outer rampart brightened with ejecta and the upper portion of a terraced inner wall, but lacks the ray system associated with younger craters. A triangular promontory extends 30 kilometers from the southeast of the rim.

The interior of the crater lacks a central peak, and is flooded with lava. It is devoid of significant raised features, although there are a few tiny meteor craters near the rim. Scattered wisps of bright ray material lie across the floor, most likely deposited by the impact that created Autolycus.

The stretch of lunar surface between Archimedes and Autolycus was the site of the crash-landing of the Soviet probe Luna 2. This was the first craft to reach the surface of the Moon, landing September 13, 1959.

Archimedes of Syracuse (Greek: Ἀρχιμήδης; c. 287 BC – c. 212 BC) was an Ancient Greek mathematician, physicist, engineer, inventor, and astronomer. Although few details of his life are known, he is regarded as one of the leading scientists in classical antiquity. Generally considered the greatest mathematician of antiquity and one of the greatest of all time, Archimedes anticipated modern calculus and analysis by applying concepts of infinitesimals and the method of exhaustion to derive and rigorously prove a range of geometrical theorems, including the area of a circle, the surface area and volume of a sphere, and the area under a parabola.

Archimedes died during the Siege of Syracuse when he was killed by a Roman soldier despite orders that he should not be harmed. Cicero describes visiting the tomb of Archimedes, which was surmounted by a sphere and a cylinder, which Archimedes had requested to be placed on his tomb, representing his mathematical discoveries.

Planetarium (orrery)
After the capture of Syracuse c. 212 BC, General Marcus Claudius Marcellus is said to have taken back to Rome two mechanisms, constructed by Archimedes and used as aids in astronomy, which showed the motion of the Sun, Moon and five planets. Cicero mentions similar mechanisms designed by Thales of Miletus and Eudoxus of Cnidus. The dialogue says that Marcellus kept one of the devices as his only personal loot from Syracuse, and donated the other to the Temple of Virtue in Rome.

"When Gallus moved the globe, it happened that the Moon followed the Sun by as many turns on that bronze contrivance as in the sky itself, from which also in the sky the Sun's globe became to have that same eclipse, and the Moon came then to that position which was its shadow on the Earth, when the Sun was in line."

The Sand Reckoner
In this treatise, Archimedes counts the number of grains of sand that will fit inside the universe. This book mentions the heliocentric theory of the solar system proposed by Aristarchus of Samos, as well as contemporary ideas about the size of the Earth and the distance between various celestial bodies. By using a system of numbers based on powers of the myriad, Archimedes concludes that the number of grains of sand required to fill the universe is 8×1063 in modern notation. The introductory letter states that Archimedes' father was an astronomer named Phidias. The Sand Reckoner or Psammites is the only surviving work in which Archimedes discusses his views on astronomy.

Excerpts from Wiki texts have been incorporated into the blog as kinds of abstracts for reader's convenience. By clicking the links much more can be learned about these subjects.

Moon: Theaetetus

"Theaetetus crater 4103 h1 4103 h2" by James Stuby based on NASA image
Lunar Orbiter 4 photo via Commons
Theaetetus Crater
Theaetetus is a lunar impact crater that is located to the southeast of the crater Cassini near the eastern edge of Mare Imbrium. It lies just to the west of the Montes Caucasus range, which forms the eastern shore of the mare. To the southwest is the prominent crater Aristillus.
The rim of Theaetetus is distinctly polygonal in shape, with a slight rounding at the vertices. There is a low outer rampart and a slight central rise on the crater floor, which is offset to the northeast of the crater midpoint. The interior is otherwise relatively featureless.

This crater has been noted in the past as a site of possible transient lunar phenomena. In 1902, a white cloud was observed briefly in the vicinity of the crater. Other observers, including Patrick Moore and W. H. Pickering, have also noted unusual appearances in this area.

Theaetetus of Athens
Theaetetus of Athens (Greek: Θεαίτητος; c. 417 – 369 BC), possibly the son of Euphronius of the Athenian deme Sunium, was a Greek mathematician. His principal contributions were on irrational lengths, which was included in Book X of Euclid's Elements, and proving that there are precisely five regular convex polyhedra.  A friend of Socrates and Plato, he is the central character in Plato's eponymous Socratic dialogue.

Theaetetus, like Plato, was a student of the Greek mathematician Theodorus of Cyrene (5th century BC).  Cyrene was a prosperous Greek colony on the coast of North Africa, in what is now Libya, on the eastern end of the Gulf of Sidra. Theodorus had explored the theory of incommensurable quantities, and Theaetetus continued those studies with great enthusiasm; specifically, he classified various forms of irrational numbers according to the way they are expressed as square roots. This theory is presented in great detail in Book X of Euclid's Elements.

Accordingly, the name of this crater is unusual because Theaetetus was a mathematician but - as far as I know - is not related in any way to Astronomy like all the other Greek persons whose name is given to craters on the face of the Old Man Moon. Theaetetus of Athens is today famous mainly because of the dialogue with Socrates that was written by Plato c. 360 BC.
In this dialogue, Socrates and Theaetetus discuss three definitions of knowledge: knowledge as nothing but perception, knowledge as true judgment, and, finally, knowledge as a true judgment with an account. Each of these definitions is shown to be unsatisfactory.

Socrates declares Theaetetus will have benefited from discovering what he does not know, and that he may be better able to approach the topic in the future. The conversation ends with Socrates' announcement that he has to go to court to face a criminal indictment.

Excerpts from Wiki texts have been incorporated into the blog as kinds of abstracts for reader's convenience. By clicking the links much more can be learned about these subjects.

Wednesday, October 14, 2015

Bible references in Astrotheology blog

Bible verses in Space theology blog

1 Cor 2:3-10   .../2011/12/deep-things-of-god.html
1 Cor 2:9 .../2013/05/heavenly-father.html  
1 Kings 10:14-2    .../2012/09/gold-in-bible.html
1 Tim 6:13-16 .../2009/05/christ-true-light.html
2 Chr 2:5-6 .../2013/05/heavenly-father.html
2 Chr 36:23 .../2011/10/god-of-heaven-persia-iran.html
2 Cor 12:1-5 .../2012/10/where-is-heaven.html
2 Peter 1:14-25     .../2009/03/prolegomena-natural-religion-and.html
2 Th 2:5-10 .../2009/03/cosmic-christology.html
Acts 17:15-34 .../2012/03/apostle-paul-in-athens.html
Acts 17:23-28 .../2012/04/bible-and-beginning.html
Acts 3:6 .../2012/09/gold-in-bible.html
Amos 5:26 .../2011/10/god-of-heaven-persia-iran.html
Col 1:15-17 .../2012/07/saint-patrick-and-cosmic-christ.html
Col 1:16 .../2009/03/cosmic-christology.html
Dan 10:4-9 .../2012/08/chrysolite-in-bible.html
Dan 2:37-38 .../2011/10/god-of-heaven-persia-iran.html
Dan 2:44 .../2011/10/god-of-heaven-persia-iran.html
Dan 4:34-35 .../2011/10/god-of-heaven-persia-iran.html
Dan 4:37 .../2011/10/god-of-heaven-persia-iran.html
Dan 7:13-14 .../2011/10/god-of-heaven-persia-iran.html
Dan 7:9-10 .../2011/10/god-of-heaven-persia-iran.html
Deut 1:10 .../2011/10/abraham-looking-at-night-sky.html
Deut 17:2-7 .../2011/10/god-of-heaven-persia-iran.html
Deut 4:15-19 .../2011/10/god-of-heaven-persia-iran.html
Exodus 20:5-6 .../2012/03/god-of-israel-materialist-or-idealist.html
Exodus 28:15-19 .../2012/08/chrysolite-in-bible.html
Ezra 1:2 .../2011/10/god-of-heaven-persia-iran.html
Ezra 5:11-12 .../2011/10/god-of-heaven-persia-iran.html
Ezra 7:11-12 .../2011/10/god-of-heaven-persia-iran.html
Gen 1:1 .../2012/06/creation-of-cosmos.html
Gen 1:1 .../2012/06/time-in-Gen-1.html
Gen 1:10 .../2013/01/christ-redeemer-of-et.html
Gen 1:1-4 .../2012/06/let-there-be-light-2.html
Gen 1:14-18 .../2011/10/falling-stars-in-bible.html
Gen 1:19-22 .../2009/04/divine-lithography.html
Gen 1:24-31 .../2009/04/divine-timing.html
Gen 1:27 .../2012/08/you-cosmos-and-god.html
Gen 1:27 .../2013/01/christ-redeemer-of-et.html
Gen 1:3 .../2011/07/light-to-world.html
Gen 1:3-5 .../2009/04/light.html
Gen 1:6-8 .../2011/10/falling-stars-in-bible.html
Gen 1:9-13 .../2011/09/bible-and-origins-of-life.html
Gen 15:1-6 .../2009/03/abraham-great-sky-skaper.html
Gen 15:1-6 .../2011/10/abraham-looking-at-night-sky.html
Gen 15:1-6 .../2015/03/abraham-and-lord-stargazing.html
Gen 2:10-12 .../2012/09/gold-in-bible.html
Gen 2:1-3 .../2012/05/st-augustine-versus-bible.html
Gen 2:15-17 .../2013/01/christ-redeemer-of-et.html
Gen 2:18-19 .../2009/04/divine-lithography.html
Gen 2:7-9 .../2011/09/bible-and-origins-of-life.html
Gen 28:10-17 .../2011/10/gate-of-heaven-jacobs-dream.html
Gen 37:10-11 .../2011/10/josephs-second-dream.html
Gen 37:9 .../2011/10/josephs-second-dream.html
Heb 11:3 .../2012/03/god-of-israel-materialist-or-idealist.html
Isaiah 14:12-15 .../2011/10/mornign-star-in-biblical-world.html
Isaiah 14:12-15 .../2011/10/falling-stars-in-bible.html
Isaiah 34:4   .../2011/10/falling-stars-in-bible.html
Isaiah 38:1-8 .../2012/06/when-shadow-moved-back-for-king.html
Isaiah 40:25-31 .../2009/04/divine-timing.html
Isaiah 43:1 .../2012/08/you-cosmos-and-god.html
Isaiah 44:1-5 .../2012/12/god-of-israels-outrageous-words.html
Isaiah 44:24-28 .../2012/12/god-of-israels-outrageous-words.html
Isaiah 64:1-4 .../2011/12/deep-things-of-god.html
Isaiah 64:4   .../2013/05/heavenly-father.html
Isaiah 66:1-2 .../2012/10/where-is-heaven.html
Jeremiah 31:33-37 .../2012/04/parsec-and-cosmic-patience-of-god-of.html
Jeremiah 31:33-37 .../2012/05/parsec-and-cosmic-patience-of-god-of.html
Jeremiah 31:35-37   .../2015/10/gods-cosmic-words-about-israel.html
Jeremiah 44:19 .../2011/10/queen-of-heaven.html
Job 38:31-33 .../2015/09/biblical-astronomy-job-3831-33.html
Job 42:1-6 .../2011/10/god-man-and-cosmic-collitions.html
Job 9:1-13 .../2011/10/god-job-and-sky.html
John 1:1-14 .../2009/05/christ-true-light.html
John 1:1-5 .../2009/04/light.html
John 14:28 .../2011/04/quicumque-vult.html
John 4:2 .../2012/03/god-of-israel-materialist-or-idealist.html
John 4:22 .../2009/04/jesus-salvation-is-of-jews.html
John 4:22 .../2012/04/bible-and-beginning.html
Joshua 10:12-13     .../2012/06/when-sun-stood-still-book-of-joshua.html
Joshua 10:9-11 .../2012/06/when-sun-stood-still-book-of-joshua.html
Luke 10:17-18 .../2011/10/falling-stars-in-bible.html
Luke 2:8-16 .../2012/10/where-is-heaven.html
Mark 12:24-25 .../2013/01/christ-redeemer-of-et.html
Mark 12:3-17 .../2012/09/gold-in-bible.html
Mark 9:17-27 .../2009/03/prolegomena-scientist-and-theologian.html
Matthew 10:29 .../2012/08/you-cosmos-and-god.html
Matthew 10:30 .../2012/08/you-cosmos-and-god.html
Matthew 23:16-17 .../2012/09/gold-in-bible.html
Matthew 24:14 .../2012/10/end-of-world-and-cosmology.html
Matthew 26:62-66 .../2011/10/god-of-heaven-persia-iran.html
Matthew 5:43-48 .../2012/08/you-cosmos-and-god.html
Matthew 5:44-45 .../2012/01/his-sun.html
Matthew 5:44-45 .../2012/04/stellar-astronomy-aristotle-hegel-and.html
Matthew 5:44-45 .../2012/09/his-sun-in-action.html
Matthew 6:9-15 .../2011/10/heavenly-father.html
Nehemia 2:4   .../2011/10/god-of-heaven-persia-iran.html
Psalm 104:1 -3 .../2013/05/heavenly-father.html
Psalm 139:13-14 .../2012/11/creator-me-and-universe.html
Psalm 147:4 .../2012/08/you-cosmos-and-god.html
Psalm 8 ../2011/10/space-psalm-8.html
Psalm 8 .../2015/09/psalm-8.html
Psalm 8:3-4 .../2012/11/creator-me-and-universe.html
Rev 21:16-21 .../2012/09/gold-in-bible.html
Rev 21:19-20 .../2012/08/chrysolite-in-bible.html
Rev 6:13-18 .../2011/10/falling-stars-in-bible.html
Romans 1:18-23   .../2009/03/prolegomena-scientist-and-theologian.html
Romans 1:18-23 .../2009/05/matter-of-eter

Moon: Endymion

Oblique Lunar Orbiter 4 image facing west
James Stuby based on NASA image via Commons
Endymion Crater
Endymion is a lunar crater that lies near the northeast limb of the Moon. It is located to the east of Mare Frigoris, and north of the Lacus Temporis. To the southwest is the somewhat smaller crater Atlas. Because of its location, Endymion has an oval appearance from foreshortening. Beyond the crater along the lunar limb is the Mare Humboldtianum.

The floor of Endymion has been covered in low-albedo lava that gives it a dark appearance and makes it relatively easy to locate. The floor is nearly smooth and featureless, with only a few tiny craterlets located within the rim. A string of three lie near the northwestern inner wall. Faint streaks of ray material from Thales to the north-northwest crosses the dark floor. The outer rampart is low, wide, and worn from impact erosion.

"Girodet - Sommeil Endymion" by Anne-Louis Girodet de Roussy-Trioson
User:Jastrow. Licensed under CC BY-SA 3.0 via Commons

The face of the Old Man Moon is marked with craters many of which have been named after Greek and Roman astronomers that have contributed to the study of the space. The name Endymion is an exception as it does not refer to any ancient astronomer but rather to a purely mythological figure.
In Greek mythology, Endymion (Greek: Ἐνδυμίων, gen.: Ἐνδυμίωνος), was variously a handsome Aeolian shepherd, hunter, or king who was said to rule and live at Olympia in Elis, and he was also venerated and said to reside on Mount Latmus in Caria, on the west coast of Asia Minor.
So why on Earth was the name of a purely mythological figure given to a crater located in Mare Frigoris? Well, for a good reason: Endymion was loved by Selene, the Titan goddess of the moon. He was said to be the first human to observe the movements of the moon. Alghough ancient Greeks called him first a shepherd later, by the time of Pliny the Elder (AD 23 - 79), he was also known as an astronomer (Pliny, Naturalis Historia Book II.IV.43.)

The Myth
Apollonius of Rhodes (first half of 3rd century BC) is one of the many poets who tell how Selene, the Titan goddess of the moon, loved the mortal. She believed him to be so beautiful that she asked Endymion's father, Zeus, to grant him eternal youth so that he would never leave her.

Alternatively, Selene so loved how Endymion looked when he was asleep in the cave on Mount Latmus, near Miletus in Caria, that she entreated Zeus that he might remain that way.

In either case, Zeus granted her wish and put him into an eternal sleep. Every night, Selene visited him where he slept. Selene and Endymion had fifty daughters who are equated by some scholars with the fifty months of the Olympiad.

According to a passage in Deipnosophistae, the sophist and dithyrambic poet Licymnius of Chios tells a different tale, in which Hypnos, the god of sleep, in awe of his beauty, causes him to sleep with his eyes open, so he can fully admire his face.
Moon craters are not only history of science. Beautiful Selene on the night sky has inspired beautiful stories of love and great art among humanity through the ages!

Excerpts from Wiki texts have been incorporated into the blog as kinds of abstracts for reader's convenience. By clicking the links much more can be learned about these subjects.