Theoretical astronomy

Completion status: Ready for testing by learners and teachers. Please begin!

Theoretical astronomy at its simplest is the definition of terms to be applied to astronomical phenomena. In essence it is the theory of the science of physical and logical laws with respect to any natural body in the sky especially at night.

Educational level: this is a secondary education resource.

As many of the first terms a student encounters regarding natural bodies in the sky are at a secondary level, this learning resource starts there, proceeds through a university undergraduate level, dwells occasionally at the graduate or postgraduate level (often called postdoctoral) and ultimately focuses on the state of the art and a bit beyond. Enjoy!

Educational level: this is a tertiary (university) resource.

This resource is in part a lecture and in part an article.

Educational level: this is a research resource.

Speculation, though, is seldom put into an article, but to stimulate the imagination and perhaps open a few doors that may seem closed at present, cautionary speculation based somewhat on current knowledge is included.

Resource type: this resource contains a lecture or lecture notes.

Part of the fun of theory is extending the known to what may be known to see if knowing is really occurring, or is it something else.

Resource type: this resource is an article.

The laboratories of astronomy are limited to the observatories themselves. The phenomena observed are located in the heavens, far beyond the reach, let alone control, of the astronomical observer. “So how can one be sure that what one sees out there is subject to the same rules and disciplines of science that govern the local laboratory experiments of physics and chemistry?” “The most incomprehensible thing about the universe is that it is comprehensible.” - Albert Einstein.

Subject classification: this is an astronomy resource.

Universals

Subject classification: this is a science resource .

The overall theory of astronomy consists of three fundamental parts:

1. the derivation of logical laws,
2. the definitions of natural bodies (entities or objects), and
3. the definition of the sky (and associated realms).

Notation

To help with definitions, their meanings and intents, the learning resource Theory of definition comes in handy.

Notation: Let the letters "Def." indicate that a definition is following.

Sky

Although the image contains a layer of cumulus clouds, at the horizon, the Atlantic Ocean meets the edge of the sky. Location :Salvador, Bahia, Brazil, July 4, 2008. Credit: Tiago Fioreze.

Def. "the expanse of space that seems to be over the earth like a dome" is called the sky, or the sometimes the heavens.

This is a 360° view of the surrounding terrain, horizon and Martian sky, taken on November 23-28, 2005, by the Exploration Rover 'Spirit'. Credit: NASA.

This definition applies especially well to an individual on top of the Earth's solid crust looking around at what lies above and off to the horizon in all directions. Similarly, it applies to an individual's visual view while floating on a large body of water, where off on the horizon is still water.

A view of the horizon on the Moon's solid surface shows a black sky without stars because of sunlight coming from the left. Credit: NASA.

The image at right shows the horizon marking the lower edge of the sky and the upper edge of the Atlantic Ocean, with a layer of cumulus clouds just above.

A more general definition of 'sky' allows for skies as seen on other worlds. At left is a 360° panarama of the horizon on Mars as perceived in the visual true-color range of the NASA Mars Exploration Rover 'Spirit' on November 23-8, 2005.

Def. an "expanse of space that seems to be [overhead] like a dome" is called a sky.

Even in day light, the sky may seem absent of objects if a nearby source tends to overwhelm other luminous objects.

At right is a view of the horizon on the Moon's solid surface taken by an Apollo 16 astronaut. The image shows a black sky without stars because the sunlight coming from the left is overwhelming.

Entities

Def.

1.a: an "independent, separate, or self-contained existence",

1.b: "the existence of a thing as contrasted with its attributes", or

2. "something that has separate and distinct existence and objective or conceptual reality",

is called an entity.

Def.

1.a: "something that is or is capable of being seen, touched, or otherwise sensed",

1.b: "something physical or mental of which a subject is cognitively aware",

2. "something that arouses an emotion in an observer", or

3. "a thing that forms an element of or constitutes the subject matter of an investigation or science"

is called an object.

Def.

1.a: "a mass of matter distinct from other masses" or

2.b: "something that embodies or gives concrete reality to a thing; [specifically] : a sensible object in physical space"

is called a body.

Def.

1.a: "a separate and distinct individual quality, fact, idea, or [usually] entity",

1.b: "the concrete entity as distinguished from its appearances",

1.c: "a spatial entity", or

1.d: "an inanimate object distinguished from a living being"

is called a thing.

Def.

1: "an observable fact or event",

2.a: "an object or aspect known through the senses rather than by though or intuition",

2.b: "an object of experience in space and time as distinguished from a thing-in-itself", or

2.c: "a fact or event of scientific interest susceptible of scientific description and explanation"

is called a phenomenon.

Such words as "entity", "object", "thing", and perhaps "body", words "connoting universal properties, ... constitute the very highest genus or "summum genus"" of a classification of universals. To propose a definition for say a plant whose flowers open at dawn on a warm day to be pollinated during the day time using the word "thing", "entity", "object", or "body" seems too general and is. But, astronomy deals with the universe, sometimes only the very local universe just above the Earth's atmosphere. These "universals" may be just the words to use.

Meaning

On the basis of dictionary definitions, what is the difference between a 'body', an 'entity', an 'object', a 'thing', and a 'phenomenon'?

The categories for synonymy and most common usage place 'body' in "3. SUBSTANTIALITY", 'entity' in the same, 'object' in "651. INTENTION", 'thing' in "3. SUBSTANTIALITY", and 'phenomenon' in "918. WONDER". The more common uses of the words 'object' and 'phenomenon' are not exactly the same as may be used in a specialized endeavor like a science such as astronomy. A slightly less common use of 'phenomenon' is in category "150. EVENTUALITY". For the word 'object' a slightly less common or popular meaning is in category "543. MEANING". The closest category of meaning or synonymy for 'object' to category 1. is category "375. MATERIALITY".

Of each of these words, 'entity' uses the word 'existence', category "1. EXISTENCE" in each definition. 'Entity' may be thought of as the most general of these terms because its meanings are the closest to category 1. The farthest from category 1. on the basis of conceptual meaning and synonymy is the word 'object' in category 375. A tentative order is 'entity' > 'phenomenon' > 'object' by generalness, or by preciseness (perhaps more description is needed beyond only existence) 'object' > 'phenomenon' > 'entity'.

'Thing' (category 3.) has the word 'entity' in three of four meanings and 'object' in the fourth. The second most popular meaning of 'thing' is in category 375.

'Body' (category 3.) has 'mass' and is closer to 'substantiality' in common usage than 'thing', and neither word has a synonym closer in meaning to 'existence'. The second most common meaning of 'body' is category "203. BREADTH, THICKNESS".

This suggests a hierarchy such as 'entity' > 'body' > 'thing' > 'phenomenon' > 'object' by generalness, where 'existence' is the most general word; or, 'object' > 'phenomenon' > 'thing' > 'body' > 'entity' by preciseness. An 'astronomical object' may be expected to require a more detailed description in its definition to indicate meaning than an 'astronomical entity'. In astronomy, the concept of an 'astronomical body' may suggest a meaning closer to category 203. rather than a 'thing' or 'entity'.

The choice of general order is 'entity' > 'source' > 'object' > 'phenomena'. The term 'astronomical body' has much less popularity per Google scholar than 'object'. The body of astronomers in the International Astronomical Union is auspicious and here is considered an astronomical entity.

Def. the theory of the science of the biological, chemical, physical, and logical laws (or principles) with respect to any natural being, body, thing, entity, source, object, or phenomena in the sky especially at night is called theoretical astronomy.

Astronomical entity

Def.

1.a: an "independent, separate, or self-contained [astronomical] existence",

1.b: "the [astronomical] existence of a [person, place, or] thing as contrasted with its attributes", or

2. "some [astronomical] thing that has separate and distinct existence and objective or conceptual reality",

is called an astronomical entity.

By generalness, 'being' > 'entity' > 'phenomenon' > 'object'. Further, 'being' > 'body' > 'something' or 'thing' > 'entity'.

What are some astronomical entities?

"[V]oids [are] now considered as regular astronomical entities in their own rights, [and] are clustered."

There are "a plethora of observations from heavenly bodies which did not agree with each other despite being from the same astronomical entities." The observations themselves, media of recording, and the heavenly bodies are all astronomical entities. So are the observers and astronomers who make or made the records. Constellations are astronomical entities. 'Sky' is an astronomical entity.

Included as astronomical entities are 'astronomical objects' and 'astronomical sources', even those with large error regions of whole degrees. Diffuse background radiations, whether gamma ray or radio, are astronomical entities.

"Astronomical named entities":

1. "Names of telescopes and other measurement instruments,"
2. "Names of celestial objects,"
3. "Types of objects," and
4. "Features that can be pointed to on a spectrum".

"Gazetteers are useful for finding commonly referenced names of people, places or organisations" associated with astronomy. These are astronomical entities that can be used for information processing.

Astronomical entities include some journals (such as The Astrophysical Journal, the Monthly Notices of the Royal Astronomical Society, and Astronomy & Astrphysics), articles in journals and magazines, books on astronomy that may be references or be cited for astronomy information or facts.

Named entity recognition (NER) for astronomy literature: NER "involves assigning broad semantic categories to entity references in text."

Types of entities for Natural Language Processing (NLP):

1. names - person, location, organization;
2. temporal expressions - date, time;
3. numeric expressions - money, percent;
4. instrument name;
5. source name;
6. source type;
7. spectral feature; and
8. text and scientific databases.

"Astronomy is a broad scientific domain combining theoretical, observational and computational research, which all differ in conventions and jargon." "There is a major effort in astronomy to move towards integrated databases, software and telescopes." ("The Virtual Observatory").

Entity categories include 'galaxy', 'nebula', 'star', 'star cluster', 'supernova', 'planet', 'frequency', 'duration', 'luminosity', 'position', 'telescope', 'ion', 'survey', and 'date'.

Dominant group

The term "dominant group" is used in astronomy to identify other astronomical entities of importance. The genera differentia for possible definitions of "dominant group" fall into the following set of orderable pairs:

Genera differentia for "dominant group"

Synonym for "dominant"	Category Number	Category Title	Synonym for "group"	Category Number	Catgeory Title
“superior”	36	SUPERIORITY	"arrangement"	60	ARRANGEMENT
“influential”	171	INFLUENCE	"class"	61	CLASSIFICATION
“musical note”	462	HARMONICS	"assembly"	74	ASSEMBLAGE
“most important”	670	IMPORTANCE	"size"	194	SIZE
“governing”	739	GOVERNMENT	"painting", "grouping"	572	ART
"master"	747	MASTER	"association", "set"	786	ASSOCIATION
-----	---	-------	"sect"	1018	RELIGIONS, CULTS, SECTS

'Orderable' means that any synonym from within the first category can be ordered with any synonym from the second category to form an alternate term for "dominant group"; for example, "superior class", "influential sect", "master assembly", "most important group", and "dominant painting". "Dominant" falls into category 171. "Group" is in category 61. Further, any word which has its most or much more common usage within these categories may also form an alternate term, such as "ruling group", where "ruling" has its most common usage in category 739, or "dominant party", where "party" is in category 74.

dominant group

"A particular subject of interest is the cluster ion series (NH₃)_nNH₄⁺, since it is the dominant group of ions over the whole investigated temperature range." For astrochemisty, "[t]hese studies are expected to throw light on the sputtering from planetary and interstellar ices and the possible formation of new organic molecules in CO--NH₃–H₂O ice by megaelectronvolt ion bombardment."

All alternate terms for "dominant group" used in astronomy are astronomical entities. Here are some examples from the literature:

master class

1. "Once created, device class objects are registered with an instance of the master class."
2. "For ATIC, a possible set of defined classes would be a master class event, and sub-classes header, silicon, scintillator, bgo and track."

superior size

1. "The superior size and albedo of Venus completely turn the scale, with the result that Venus at her brightest is about 12 times brighter than Mercury at his brightest."
2. "There is no reason to question but that they are simply ordinary meteors, which from their superior size and unusually slow speed have survived to reach the earth's surface."

influential set

1. "Together with Leonard Searle, he wrote an influential set of papers which established that stellar disks are truncated at about four exponential scale-lengths, and that the vertical scale-height of disks is constant with radius."
2. "Until now Themo has been best known for an influential set of questions on Aristotle's Meteorologica, which is closely related to similar sets by Nicole Oresme and, putatively, Simon Tunsted."

Astronomical source

The image is some of the astronomical sources within the error circle around Serpens XR-1, (X-ray, XR), an early X-ray source. Legend: red * - star, X - X-ray source, LMXB - low-mass X-ray binary (Serpens X-1), Mira - Mira variables, gammaBurst - gamma-ray burst source, DkNeb - dark nebula, RRLyr - RR Lyrae variable star, Cepheid - Cepheid variable star. Credit: Aladin at SIMBAD.

Def. a natural source usually of radiation in the sky especially at night is called an astronomical source.

An astronomical source may have generated or be capable of generating electromagnetic radiation, a star, or a galaxy, for example. A source reflects, generates, or fluoresces that which may be detectable.

A celestial source is any astronomical source except the Earth.

An astronomical source usually has a spatial, temporal, intensity, and spectral profile. Such a profile may be continuous, intermittent, transient, fluctuating, aperiodic, or unpredictable.

Some astronomical objects are not detectable directly as a source but instead may be absorbers of a portion of a signal from an object further away.

The image at right is a celestial map of the astronomical sources within the original detected error circle around the first astronomical X-ray source discovered in the constellation Serpens Cauda (Serpens XR-1, or Serpens X-1). The other sources within this error circle are stars, other X-ray sources, a gamma-ray burst source, and a dark nebula.

Astronomical object

This view of the rising Earth greeted the Apollo 8 astronauts as they came from behind the Moon after the lunar orbit insertion burn. Credit: NASA.

The science of astronomy consists of three fundamental parts:

1. physical and logical laws,
2. any natural object, and
3. the sky.

The SIMBAD reference database "contains identifications, 'basic data', bibliography, and selected observational measurements for several million astronomical objects." "The specificity of the SIMBAD database is to organize the information per astronomical object". "Building a reference database for ... all astronomical objects outside the Solar System – has been the first goal of the CDS". "The only astronomical objects specifically excluded from SIMBAD are the Sun and Solar System bodies."

Def. a natural object in the sky especially at night is called an astronomical object.

This true-color image shows North and South America as they would appear from space 35,000 km (22,000 miles) above the Earth. Credit: Reto Stöckli, Nazmi El Saleous, and Marit Jentoft-Nilsen, NASA GSFC.

As indicated above about the astronomical objects in the SIMBAD database and in the learning reference astronomy, there are many objects between the observer on the ground atop some portion of the Earth's crust and astronomical objects other than the Sun and Solar System bodies. Further, for those observers looking toward the Earth from another location such as near the Moon in the photograph at above right, it seems that the Earth is a natural object. On the Earth 384,000 km away, the sunset terminator bisects Africa.

A closer view of Earth shows some of the astronomical objects near the Earth and apparently just above the surface, where an observer may be. Some of these objects such as clouds probably by convention are more likely to be studied by planetary observers, or weather observers, rather than astronomical observers.

With perspectives other than upwards from the Earth's crustal surface, the word "sky" may seem insufficient or inappropriate, although studying the Earth as part of planetary science may leave interesting astronomical objects near the Earth that are occasionally "in the sky". The idea being that the Earth cannot be in its own sky, or can it? Perhaps, it is more a matter of whether other observers agree that what an observer is observing is astronomy or planetary science, or both.

Star by dictionary

For the object, "star", a dictionary definition is

1.a: "any natural luminous body visible in the sky [especially] at night",

1.b: "a self-luminous gaseous celestial body of great mass whose shape is [usually] spheroidal and whose size may be as small as the earth or larger than the earth's orbit".

This definition seems okay for a dictionary, but is it adequate for a science, and especially, astronomy?

Astrochemistry

Subject classification: this is a chemistry resource .

Def. "[t]he study of the chemical composition of stars and outer space", per Wiktionary astrochemistry, is called astrochemistry.

"An important goal for theoretical astrochemistry is to elucidate which organics are of true interstellar origin, and to identify possible interstellar precursors and reaction pathways for those molecules which are the result of aqueous alterations."

Atmosphere

Def. "a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body", per the Wikipedia article atmosphere, is called an atmosphere.

Def. "[t]he gases surrounding the Earth or any astronomical body", per Wiktionary atmosphere, is called an atmosphere.

Interplanetary medium

Def. "[t]hat part of outer space between the planets of a solar system and its star", from Wiktionary interplanetary space, is called interplanetary space.

Def. "the material which fills the solar system and through which all the larger solar system bodies such as planets, asteroids and comets move", from the Wikipedia article interplanetary medium, is called an interplanetary medium.

Ions

Def. "[a]n atom or group of atoms bearing an electrical charge such as the sodium and chlorine atoms in a salt solution", from Wiktionary ion, is called an ion.

Materials

Def. "[m]atter which may be shaped or manipulated, particularly in making something", per Wiktionary materials, is called a material.

Def. "[a]ny instrument used in astronomy for observing distant objects", from Wiktionary telescope, is called a telescope.

Def. "[a]n object, usually made of glass, that focuses or defocuses the light [or an electron beam] that passes through it", per Wiktionary lens, is called a lens.

Meteorite

Def. "[a] metallic or stony object that is the remains of a meteor", from Wiktionary meteorite, is called a meteorite.

Shelter

Def. "[a] refuge, haven or other cover or protection from something", per Wiktionary shelter, is called a shelter.

Def. "[a]nything shaped like [a common structural element of architecture that resembles the hollow upper half of a sphere, a cupola], often used as a cover", after Wiktionary dome, is called a dome.

Astrophysics

Subject classification: this is a physics resource .

“Contrary to the belief generally held by laboratory physicists, astronomy has contributed to the growth of our understanding of physics.”

Theoretical astronomy seeks to understand what is behind cosmic events by taking the physics from the laboratory and testing it in models against the data obtained from observations. This is usually referred to as astrophysics. But, often the observations seem more than just what the physics can describe. Adding in extra tidbits may help to describe and help to produce better agreement. If these extra tidbits are physical in nature, they are part of theoretical astrophysics, if astronomical in nature, then theoretical astronomy.

Astronomical units

Def. "1 day (d)" is called the astronomical unit of time.

Def. "365.25 days" is called a Julian year.

Def. "36,525 days" is called a Julian century.

Def. "the distance from the centre of the Sun at which a particle of negligible mass, in an unperturbed circular orbit, would have an orbital period of 365.2568983 days" is called the Astronomical Unit (AU).

Def. "the mass of the Sun" is called the astronomical unit of mass.

Def. "the rate at which a star radiates energy in all directions", per Wiktionary luminosity, is called luminosity.

Def. "the distance at which one Astronomical Unit subtends an angle of one arcsecond" is called the parsec (pc).

Def. "the distance traveled by light in one Julian year in a vacuum" is called the light-year (ly).

Aurora

Laboratory experiment produces aurora at the poles of a sphere. Credit: David Monniaux.

Computer simulations are usually used to represent auroras. The image at right shows a terrella in a laboratory experiment to produce auroras.

Fluctuating visible source

At the bottom of this visible emission model is a visual intensity curve. Credit: Stanlekub.

Consider only that portion of the emission of the visible source at right that is a level maximum. If this is the first observation received, a reasonable theoretical explanation from physics is a constant black body visible source, like a light bulb. In a physics laboratory, a steady voltage/current power supply produces a steady intensity.

Now consider the full length observation indicated by the moving green circle. From a physics perspective, it appears the power supply is not steady. Using alternating current (AC) to power the light bulb at 60 cycles per second may trigger the detector to yield an oscillatory intensity curve if its response time is short enough to resolve the use of AC. This is a possible theoretical physics; hence, theoretical astrophysics additional explanation of what may be happening.

A theoretical astronomy explanation is indicated in the colorful figure above as two visible sources, unresolved by the detector (seen only as a point source), but possibly responsible for the changes in the visible light received at the detector. Which do you think is more likely: a fluctuating power supply or an eclipsing binary?

Physics deals with forces, fields, energy, kinetics, and radiation. Astronomy has its own laws with respect to entities or bodies in motion. Application of a field to an astronomical phenomenon may clarify what is happening. That's the focus of astrophysics. Theory is needed to bring the physics in line with the magnitude of the situation and its complexity.

Luminosity

From the Wikipedia about luminosity, "The luminosity of stars is measured in two forms: apparent (visible light only) and bolometric (total radiant energy). (A bolometer is an instrument that measures radiant energy over a wide band by absorption and measurement of heating.) When not qualified, "luminosity" means bolometric luminosity, which is measured either in the SI units, watts; or in terms of solar luminosities, $L_{\odot}$, that is, how many times as much energy the object radiates as the Sun ...

Luminosity is an intrinsic measurable property independent of distance, and is appraised as absolute magnitude, corresponding to the apparent luminosity in visible light of a star as seen at the interstellar distance of 10 parsecs, or bolometric magnitude corresponding to bolometric luminosity. In contrast, apparent brightness is related to the distance by an inverse square law. In addition to this brightness decrease from increased distance there is an extra linear decrease of brightness for interstellar "extinction" from intervening interstellar dust. Visible brightness is usually measured by apparent magnitude. Both absolute and apparent magnitudes are on an inverse logarithmic scale, where 5 magnitudes increase counterparts a 100th part decrease in nonlogarithmic luminosity.

By measuring the width of certain absorption lines in the stellar spectrum, it is often possible to assign a certain luminosity class to a star without knowing its distance. Thus a fair measure of its absolute magnitude can be determined without knowing its distance nor the interstellar extinction, and instead the distance and extinction can be determined without measuring it directly through the yearly parallax. Since the stellar parallax is usually too small to be measured for many far away stars, this is a common method of determining distances."

"[T]he luminosity of a star $L$ (assuming the star is a black body, which is a good approximation) is also related to temperature $T$ and radius $R$ of the star by the equation:

$L = 4\pi R^2\sigma T^4 \,$

where

σ is the Stefan-Boltzmann constant 5.67x10^-8 W·m^-2·K^-4" per the Wikipedia about luminosity.

Per the Wikipedia about luminosity, "Given a visible luminosity (not total luminosity), one can calculate the apparent magnitude of a star from a given distance:

$m_{\rm star}=m_{\rm sun}-2.5\log_{10}\left({ L_{\rm star} \over L_{\odot} } \cdot \left(\frac{ d_{\rm sun} }{ d_{\rm star} }\right)^2\right)$

where

m_star is the apparent magnitude of the star (a pure number)

m_sun is the apparent magnitude of the Sun (also a pure number)

L_star is the visible luminosity of the star

$L_{\odot}$ is the solar visible luminosity

d_star is the distance to the star

d_sun is the distance to the Sun".

Nucleosynthesis

"Our calculations show that production of [lithium] in low-energy flares [by nucleosynthesis], taking place in the surfaces of T Tauri-like stars, is energetically possible and can give the observed excesses over the interstellar abundance."

Nucleosynthesis

Stellar nucleosynthesis Big Bang nucleosynthesis Supernova nucleosynthesis Cosmic ray spallation

Related topics

Astrophysics Nuclear fusion R-process S-process Nuclear fission

edit

"[T]here is evidence of lithium production in some stars due to some undefined mechanism. The observations show that the Li abundance on some red giants ... and young stars exceeds the average abundance in the universe by 2 orders of magnitude". It is "suggested that Li produced in the helium envelopes of red giants comes to the surface of the stars as the result of a strong convection." For young stars, "the production of the light elements in nonthermal nuclear reactions seems the most appropriate mechanism that can be responsible for enrichment of stellar photospheres by Li." "At least 0.3 metric tons of excited Li and Be nuclei were produced during the solar flare of 1991 November 15. One can estimate the equilibrium concentration of ⁷Li nuclei in the solar atmosphere by assuming that they are produced only in solar flares and that a leakage of Li nuclei occurs with the solar wind."

Although ⁷Be is usually assumed to have been produced by the Big Bang nuclear fusion, excesses (100x) of the isotope on the leading edge of the Long Duration Exposure Facility (LDEF) relative to the trailing edge suggest that "most of the sun's fusion must occur near the surface rather than the core." The particular reaction

³He(α,γ)⁷Be

³He + ⁴He → ⁷Be + γ (429 keV)

and the associated reaction chains

⁷Be(e^-,ν_e)⁷Li(p,α)α

and

⁷Be(p,γ)⁸B → 2α + e⁺ + ν_e

generate 14% and 0.1% of the α-particles, respectively, and 10.7% of the present-epoch luminosity of the Sun. Usually, the ⁷Be produced is assumed to be deep within the core of the Sun; however, such ⁷Be would not escape to reach the leading edge of the LDEF.

Star

Def. "any object forming on a dynamical timescale, by gravitational instability", is called a star.

Starspots

Several periodic cycles are evident in the continuous recording of sunspots, most notably the 11 year (131 ± 14 month) cycle. The green line represents continuous monthly averages reported by the Solar Influences Data Center since 1749. Credit: Slashme.

"[T]here have been three possible periods of marked solar anomaly during the last 1000 years: the Maunder Minimum, another minimum [the Spörer Minimum] in the early 16th century, and a period of anomalously high activity in the 12th and early 13th centuries."

From the Wikipedia article solar cycle: "The basic causes of the solar variability and solar cycles are still under debate, with some researchers suggesting a link with the tidal forces due to the gas giants Jupiter and Saturn, or due to the solar inertial motion."

Weak equivalence principle

From the Wikipedia article equivalence principle on the weak equivalence principle: "All test particles at the alike spacetime point in a given gravitational field will undergo the same acceleration, independent of their properties, including their rest mass."

"The observation of a neutrino burst within 3 h of the associated optical burst from supernova 1987A in the Large Magellanic Cloud provides a new test of the weak equivalence principle, by demonstrating that neutrinos and photons follow the same trajectories in the gravitational field of the galaxy."

Geography

Subject classification: this is a geography resource .

The geography applicable to astronomy may be designated 'astrogeography'. But, this term is often more restricted. "[T]he relationship between outer-space geography and geographic position (astrogeography), and the evolution of current and future military space strategy" has been identified and evaluated.

Def. "[a] place where stars, planets and other celestial bodies are observed", per Wiktionary observatory, is called an observatory.

From the Ebers Papyrus, a year has 360 days of twelve months of thirty days each.

"A period of 360 days, comprising 12 months of 30 days each, was assigned by the Mesopotamians to the year in days and months at least by the third millennium BC."

In ancient Iran (Persia), the year was 360 days with 12 months of 30 days each.

"All Veda [India] texts speak uniformly and exclusively of a year of 360 days [12 months of 30 days each]. Passages in which this length of the year is directly stated are found in all the Brahmanas." This period dates to approximately the third millennium (~5,000 b2k).

An ancient Chinese calendar had a 360 day year of twelve months of thirty days each.

The Mayans had an old tradition that the year had twelve months of thirty days each, 360 days in a year.

"The Peruvian year was divided into twelve Quilla, or moons, of thirty days."

Apparently, with each of these locations around the globe and several others near to the Mediterranean Sea, the year had exactly 360 days of 12 months of 30 days each, then at some point near 2700 b2k the year became lengthened to today's year.

History

Subject classification: this is a history resource .

Def. (from 1945) "those parts of human interest in celestial phenomena which are amenable to mathematical treatment" are called astronomy. This is Neugebauer's definition of astronomy.

Def. "the search for astronomical strata whose contents could be classified" is called astronomy. This is Herschel's definition of astronomy.

"Mere "star ordering" is not "astronomy", so far as the modern usage of the term implies, regardless of the word's etymology".

Def. (from 2000) "the accurate mapping of the heavens in order to make possible the accurate prediction of phenomena" is called astronomy.

Def. "the study of objects and matter outside the Earth's atmosphere and of their physical and chemical properties" is called astronomy.

Electrical Sun

"[T]he solar corona is eminently variable, and therefore like our aurora borealis, which is known to be electric." "This vast electric mass must have a great electric repulsion through vacant space, and it lends probability to my position that it drives away from the sun the tails of comets and our zodiacal light and aurora borealis." "Electricity alone can repel electricity." "[T]he direction of the comets' tails is but the interaction between the sun and the comets, the same as the action between a charged prime conductor and a charged pith ball of an electric machine."

"[A] variety of geophysical and astrophysical phenomena can be explained by a net charge on the Sun of -1.5 x 10²⁸ e.s.u." This figure was later reduced by a factor of five.

"There appears to be considerable misunderstanding on the part of physicists of the nature and degree of the observational support of gravitational theory. For example, it appears to be commonly believed that the observations of planetary motion agree with computed orbits to the accuracy of the observations. On the other hand, it has long been known by the astronomers that there are sizable systematical discrepancies between computed and observed orbits".

Milky Way

Democritus "lived at Abdère 300 years before the Christian era [2300 b2k]. In a short fragment quoted by Plutarch, he declares that the Milky Way is an agglomeration of small stars too far away to be perceived singly."

Solar corona

The solar corona is photographed between 1901-2. Credit: Popular Science Monthly Volume 60.

"Beginning with the daguerreotype of the corona of 1851, the Reverend Lecturer had thrown on the screen pictures illustrating the form of the corona in different years. The drawings of those of 1867, 1878, and 1900 all showed long equatorial extensions with openings at the solar poles filled with beautiful rays." "The intermediate years, as, for example, 1883, 1886, and 1896 showed the four groups of synclinals which mainly constitute the corona gradually descending towards the equator of the sun, with a corresponding opening of the polar regions."

"Some of the theories of the solar corona were then illustrated and discussed."

1. "The corona is not of the nature of an atmosphere round the sun, for the pressure at the sun's limb would be enormous, while the thinness of the chromospheric lines show that it is not."
2. "comets, such as that of 1843, have approached the sun with enormous velocities within the region of the prominences without suffering disruption or retardation."
3. "If not an atmosphere of particles of gas, still less is it an atmosphere of solid stones or meteorites."
4. "Meteor streams do circle round the sun, but there is no reason why the positions of the orbits, or the intrinsic brightness of such streams should vary with the sun-spot period."
5. "the appearance of the corona does not seem to be such as the projection of meteor streams upon the celestial vault would give."
6. "Prof. Schaeberle has proposed a mechanical origin of the solar corona, due to the forces of ejection of particles from the solar limb, as evidenced by the prominences, and the force of gravity under the particular conditions of the solar rotation and the inclination of its axis to the earth's orbit."
7. "The electrical theory of the corona does not negative the mechanical theory, but supplements it. In addition to the forces of gravity and ejection, it takes account of the repulsive force which the sun exerts on matter which has the same electrical sign as itself, and which has been ejected from it."
8. "it would seem that the solar corona is of the nature of an electrical aurora round the sun."
9. "the coronoidal discharges in poor vacua obtained by Prof. Pupin about an insulated metal ball are exceedingly like the rays and streamers of the solar corona."

Zodiacal Light

The Zodiacal Light is over the Faulkes Telescope, Haleakala, Maui. Credit: 808caver.

"According to Gruson and Brugsch the Egyptians were acquainted with, and even worshipped, the zodiacal light from the very earliest times, as a phenomenon visible throughout the East before sunrise and after sunset. It was described as a glowing sheaf or luminous pyramid perpendicular to the horizon in summer, and inclined more or less during the winter. Indeed the Egyptians represented the zodiacal light under the form of a triangle which sometimes stood upright and at other times was inclined."

Mathematics

Subject classification: this is a mathematics resource .

A hyperbolic pass is indicated by the blue line with an eccentricity of 1.3. A parabolic pass is the green line. The elliptical orbit in red has an eccentricity (e) of 0.7. Credit: Stamcose.

The simplest description of the paths astronomical objects may take when passing each other includes a hyperbolic and parabolic pass. When capture occurs it usually produces an elliptical orbit.

Orbital theory

The animated elliptical orbit has an eccentricity of 0.6. Credit: Willow.

Orbits come in many shapes and motions. The simplest forms are a circle or an ellipse.

Eccentricity

"Mercury's orbit eccentricity [e] varies between about 0.11 and 0.24 with the shortest time lapse between the extremes being about 4 x 10⁵ yr". "Smaller amplitude variations occur with about a 10⁵ yr period."

Inclination

The diagram describes the parameters associated with orbital inclination (i). Credit: Lasunncty.

"The orbital inclination [i] [of Mercury] varies between 5° and 10° with a 10⁶ yr period with smaller amplitude variations with a period of about 10⁵ yr."

Obliquity

In axial tilt, the article from Wikipedia, "axial tilt (also called obliquity) is the angle between an object's rotational axis, and a line perpendicular to its orbital plane. ... The planet Venus has an axial tilt of 177.3° because it is rotating in retrograde direction, opposite to other planets like Earth. ... The planet Uranus is rotating on its side in such a way that its rotational axis, and hence its north pole, is pointed almost in the direction of its orbit around the Sun. Hence the axial tilt of Uranus is 97°."

The obliquity of the Earth's axis has a period of about 41,000 years.

Precession

The equinoxes of Earth precess with a period of about 21,000 years.

Planetary science

Subject classification: this is a science resource .

From the Wikipedia article planetary science: "Planetary science (rarely planetology) is the scientific study of planets (including Earth), moons, and planetary systems, in particular those of the solar system and the processes that form them. It studies objects ranging in size from micrometeoroids to gas giants, aiming to determine their composition, dynamics, formation, interrelations and history. It is a strongly interdisciplinary field, originally growing from astronomy and earth science, but which now incorporates many disciplines, including planetary astronomy, planetary geology (together with geochemistry and geophysics), atmospheric science, oceanography, hydrology, theoretical planetary science, glaciology, and the study of extrasolar planets. Allied disciplines include space physics, when concerned with the effects of the Sun on the bodies of the Solar System, and astrobiology."

Planet

Def. "a celestial body that

(a) is in orbit around the Sun,

(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and

(c) has cleared the neighbourhood around its orbit" is called a planet.

The proposed more general definition for a planet in orbit around another star substitutes "a star" for "the Sun" in part (a), keeps part (b), does not contain part (c), and adds "is neither a star nor a satellite of a planet."

Def. "a celestial body that

(a) is in orbit around the Sun,

(b) has sufficient mass for its self-gravity to overcome rigid forces so that it assumes a hydrostatic equilibrium (nearly round) shape,

(c) has not cleared the neighbourhood around its orbit, and

(d) is not a satellite" is called a dwarf planet.

Def. "[a]ll other objects [not a planet or dwarf planet], except satellites, orbiting the Sun" are called collectively Small Solar-System Bodies.

Def. a wanderer that is a moving light in the sky is called a planet. This is the original description meant by the word "planet".

From a theoretical planetary physics perspective: "The shape of objects with mass above 5 x 10²⁰ kg and diameter greater than 800 km would normally be determined by self-gravity, but all borderline cases would have to be established by observation."

Def. a celestial body "formed by accumulation of a rocky core, on a much longer timescale, ≳ 10⁷ yr, with subsequent acquisition of a gaseous envelope if the circumstances allow this, and with an initially fractionated elemental composition" is called a planet.

Technology

Subject classification: this is a technology resource .

This image is of the large astrolabe made by Gualterus Arsenius in 1569. Credit: David Monniaux.

From the Wikipedia article astrolabe, "the astrolabe was effectively an analog calculator capable of working out several different kinds of problems in spherical astronomy."

The Hipparcos satellite is being tested in the Large Solar Simulator at ESTEC. Credit: Michael Perryman.

Some form of an "astrolabe" may have been in use by the third millennium BC.

From the Wikipedia article: Hipparcos is "the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial objects". These measurements allow "the accurate determination of proper motions and parallaxes of stars, ... their distance and tangential velocity."

See also

• Dominant group/Astronomy
• Dominant group/Planetary science
• Galactic evolution
• Radiation astronomy
• Stellar evolution
• Theoretical radiation astronomy

Further reading

• John Woodbridge Davis (1891). Theoretical astronomy: Dynamics of the sun. New York: D. Van Nostrand Company. pp. 156. http://books.google.com/books?id=PdlJAAAAMAAJ&printsec=frontcover. Retrieved 2012-01-15. 

External links

• Bing Advanced search
• Google Books
• Google scholar Advanced Scholar Search
• International Astronomical Union
• JSTOR
• Lycos search
• NASA/IPAC Extragalactic Database - NED
• NASA's National Space Science Data Center.
• Questia - The Online Library of Books and Journals
• SAGE journals online
• The SAO/NASA Astrophysics Data System
• SDSS Quick Look tool: SkyServer
• SIMBAD Astronomical Database
• Spacecraft Query at NASA.
• SpringerLink
• Taylor & Francis Online
• Universal coordinate converter
• Wiley Online Library Advanced Search
• Yahoo Advanced Web Search

This is a research project at http://en.wikiversity.org