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Gcal 3.01

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N. Glossary

Here is an alphabetical list of most terms with short description that are introduced and used in this manual:

Actual date modifier
Gcal uses that date as today's date which is declared by the actual date modifier, instead of using the date that is given by computer's clock as system date.

Alternation operator
The `|' metacharacter is used to specify alternatives in a regular expression.

Amateur-astronomical twilight
The time when the center of the Sun passes a reference altitude of 15 degrees below a mathematical horizon.

Anchor
The `^' and `$' metacharacters in a regular expression.

ANSI
The American National Standards Institute. This organization produces many standards, among them the standards for the C and C++ programming languages.

Asr prayer time
The third Islamic prayer time. Begins in the afternoon when the length of the shadow cast by a vertical pole has a definite length, and ends just before sunset.

Astronomical twilight
The time when the center of the Sun passes a reference altitude of 18 degrees below a mathematical horizon.

Astronomical unit
An astronomical unit, abbreviated by ae, is equal to the mean distance of the Sun from the Earth, which is about 149,597,870.691 kilometers.

Autumnal equinox point on the ecliptic
The point where the descending Sun's orbit intersects the celestial equator.

Azimuth
The horizontal angular distance between the vertical circle, that passes a celestial body, and the North point.

Biorhythm
Ascending and descending curves which show three coherent biological cycles, the physical, the emotional and the intellectual cycle.

BSD
Short term for Berkeley Software Distribution, a Unix operating system variant.

C
The system programming language that most GNU software is written in.

Calendar option class
The option which control the calendar layout.

Celestial axis
The connecting line which runs between the celestial North and South Pole.

Celestial body elevation
The vertical angular distance between the celestial body and the horizon.

Celestial equator
A celestial great circle, which is vertical to the celestial axis and simultaneously represents the Earth's equator that is projected onto the celestial sphere.

Celestial Pole
The northern and southern lengthening of the Earth's rotation axis, respectively, projected on the celestial sphere.

Character class
A character class in a regular expression is a special notation for describing lists of characters that have a specific attribute, but where the actual characters themselves can vary from country to country and/or from character set to character set.

Character list
Matches any one of the characters that are enclosed in the square brackets in a text, which is processed by a regular expression.

Character set
The set of numeric codes used by a computer system to represent the characters (letters, numbers, punctuation, etc.) of a particular country or place. The most common character set in use today is ASCII (American Standard Code for Information Interchange). Many European countries use an extension of ASCII known as ISO-8859-1 (ISO Latin-1).

Civil Islamic calendar
The arithmetically determined Islamic lunar calendar.

Civil midnight time
In terms of Gcal, this is 0 o'clock, the day change just took part. This clocktime is alternatively also denoted as 24 o'clock, or 12pm.

Civil twilight
The time when the center of the Sun passes a reference altitude of 6 degrees below a mathematical horizon.

Collating element
A special sequence that can appear in a character lists of a regular expression. This apply to non-ASCII character sets, which can have single symbols that are represented with more than one character, as well as several characters that are equivalent for collating, or sorting, purposes.

Collating symbol
A multi-character collating element of a regular expression that is enclosed in `[.' and `.]' metacharacters.

Command line argument
A special text that is mostly given on the command line to run Gcal, and which serves for controlling the program.

Command
A special type of command line argument which controls the periods Gcal respects.

Common option class
The standard options all GNU software should implement at least partially.

Conjunction
A celestial body is either behind the Sun or is between Sun and Earth (seen from the Earth), and is therefore non-visible from the Earth. In terms of the Moon, this is the New Moon phase.

Critical day
Those days in the biorhythm in which one or more of the biological cycles crosses the zero point. At that time, one's system is said to be in a state of flux and it may be desirable to exhibit caution.

Cycle mode
The dynamical, i.e. depending on the respective clocktime, Sun and Moon oriented special texts are calculated for a series of clocktimes for the current day, i.e. determination is done for any time interval that can be individually defined by the user.

Date part
That part of a Gcal resource file line that contains the information at which date a fixed date happens.

Decimal system
Base-ten notation, where the digits are 0...9.

Declination
The vertical angular distance between the center of a celestial body and the celestial equator.

Delta-t
Delta-t is the difference between the Terrestrial Dynamical time (abbreviated by TDT), that was formerly known as Ephemeris time (abbreviated by ET), and the Universal time (UT). Thus, `delta-t == TDT - UT'.

Early years
In terms of eternal holidays that are determined by Gcal, these are the years within the period AD 30 until the midth of the 20th century.

Ecliptic latitude
The vertical angular distance between the center of a celestial body and the ecliptic.

Ecliptic longitude
The vertical angular distance between the center of a celestial body and the vernal equinox point on the ecliptic.

Ecliptic
The zodiacal line or Sun's orbit.

Elongation
The horizontal angular distance between the center of a celestial body and the Sun's center, as seen from the Earth.

Ending date
A part of a Gcal special text that defines the last or latest date at which the fixed date may occur.

Environment
A collection of strings, of the form name=value, that each program has available to it. Users generally place values into the environment in order to provide information to various programs. Typical examples are the environment variables HOME and PATH.

Equation of time
A correction to be added to the true solar time --as read on a sundial--- to obtain the mean solar time.

Equivalence class
A list of equivalent characters of a regular expression that is enclosed in `[=' and `=]' metacharacters.

Escape sequence
A special sequence of characters used for describing non-printing characters, such as \E or \033 or \x1B for the ASCII ESC (escape) character itself.

Evening width
Set width
The horizontal angular distance between the set azimuth of a celestial body and the West direction.

Exclusive day period
Exclusive date period
A Gcal special text that can be specified with the effect, that only those fixed dates are respected and displayed which are not part of a definite period.

Extended file name
A name that contains one ore more `/' characters, and which denotes a file, whose fixed access path either starts from the root file directory, like `/foo/bar/file', or from the actual file directory, like `./bar/file' or `../bar/file'.

Extended language code information
A simple language code information, which additionally has a territory information that is separated by a `_', like en_us for american English.

Fajr prayer time
The first Islamic prayer time. Begins with the beginning of astronomical morning twilight, and ends just before sunrise.

Fixed date option class
The options which control the fixed date layout and intensity.

Format instruction
Text variables, special texts and date formats can be provided with such an instruction text that results the special representation of the contents of text variables, and the evaluated special texts and date formats.

FSF
Free Software Foundation
A non-profit organization dedicated to the production and distribution of freely distributable software. It was founded by Richard M. Stallman, the author of the original Emacs editor.

Geocentric data
Observations of celestial bodies that are done from the fictitious center of the Earth yield in geocentrically based values.

Geocentrical horizon
That fictitious horizontal plane that passes through the Earth's center, orthogonal to the observer's local vertical.

Geometrical horizon
Mathematical horizon
Mathematical-geocentric horizon
A purely geometrically-built horizon which disregards the phenomenon of refraction as it arises in reality by the influence of the Earth's atmosphere.

Global date variable
A Gcal date variable, which is defined in the command line. Is visible in all referenced resource files.

Global option class
The options which modify the program output.

Global text variable
A Gcal text variable, which is defined in the command line. Is visible in all referenced resource files.

Gnomon
A vertical pole which is used to ascertain the length of a shadow.

GNU
GNU's not Unix. An on-going project of the Free Software Foundation to create a complete, freely distributable, POSIX-compliant computing environment.

GPL
General Public License
The terms under which Gcal and its source code may be distributed.

Gregorian calendar
The calendar which was introduced in AD 1582 by Pope Gregory XIII, that has an average year length of 365.2425 days. This calendar is most respected around the world today.

Hexadecimal system
Base 16 notation, where the digits are 0...9 and A...F, with `A' representing 10, `B' representing 11, and so on up to `F' for 15.

Highest culmination point
The highest point above or below the horizontal plane which transits a celestial body during a day.

Highlighting sequence
A control character sequence which cause a color or intensity switch in output text. Typical control character sequences are the ANSI escape sequences which have a leading escape character, and trailing more characters that define the type of the ANSI escape sequence.

Horizontal parallax
The horizontal parallax of a celestial body specifies the diameter of the Earth as it is seen from the surface of the celestial body.

Hybrid calendar mode
The automatical change from one calendar system to another if there are relations to a date for which the other calendar system is valid. Thus, Gcal automatically changes from the Julian calendar system to the Gregorian calendar system if output is related to dates after the Gregorian Reformation has happened.

Inclusive day period
Inclusive date period
A Gcal special text that can be specified with the effect, that only those fixed dates are respected and displayed which are part of a definite period.

Integer number
A whole number, i.e. a number that does not have a fractional part.

Interval expression
One or two numbers inside braces in a regular expression.

Isha prayer time
The fifth Islamic prayer time. Begins at the end of the astronomical evening twilight, and ends just before the astronomical midnight time of the Sun.

ISO
ISO is the abbreviation of International Organization for Standardization.

ISO week number
The week starts on a Monday, and the first week of a year is the one which includes the first Thursday; equivalently, the one which includes the 4th January.

Julian Ephemeris date
A Julian date that is corrected by delta-t.

Julian calendar
The calendar which was introduced in 46 BC by Julius Caesar and in the later years corrected by emperor Augustus, that has an average year length of 365.25 years. This calendar was replaced by the Gregorian calendar in AD 1582.

Julian date
Julian day number
A day number that is based on the date 1st January 4713 BCE, which is the starting day zero of a consecutive day counting used in astronomical computations. The real zero of this date is at 12 o'clock Universal time (UTC/GMT); the day does not change at midnight, but at noon Universal time.

Leap day
The 29th February in the Gregorian calendar.

Leap year
In the Gregorian calendar, a leap year is any year which number can be divided by 4 without a remainder, and years ending in hundreds are no leap years unless they are divisible by 400. But the Eastern Orthodox churches compute leap years within the Gregorian calendar by using another rule; and that, a leap year is any year which number can be divided by 4 without a remainder, and years ending in hundreds are leap years, if a remainder of 2 or 6 occurs when such a year is divided by 9.

Legal holiday
A day people don't have to work -- as in most companies, and businesses are closed; like `New Year's Day' on January 1st.

Lists of commands
Ranges of commands
Produce more than one calendar sheet per program run.

Local date variable
A Gcal date variable, which is defined in a resource file. Is visible only in this specific resource file, and that file which is included by it.

Local star time
Local sidereal time
The momentary period which is past between the last upper culmination of the vernal equinox point in the meridian of the observer's location (the momentary hour angle of the vernal equinox point), thus the right ascension of the stars in the observer's meridian at the moment.

Local text variable
A Gcal text variable, which is defined in a resource file. Is visible only in this specific resource file, and that file which is included by it.

Long-style option
A special --non-standard-- style to write an option, e.g. `--foo'.

Lowest culmination point
The lowest point below or above the horizontal plane which transits a celestial body during a day.

Lunar Arctic Circle
The geographical latitude circle that is between about 61.5 and 71.9 decimal degrees, and the geographical pole.

Lunation
Synodic month
The mean time between two consecutive New Moon phases.

Maghrib prayer time
The forth Islamic prayer time. Begins at sunset, and ends at the beginning of the Isha prayer time.

Magnitude unit
Is used to define the brightness of a star, and is a non-metrical value (Latin term magnitudo, abbreviated m). The difference between two consecutive magnitudes is 1 to 2.512. Therefore, a star with the brightness of 1m is 2.512 times brighter than a star of 2m. A negative magnitude denotes a very bright star, for example almost -27m for the Sun, whereas the hardly visible planet Pluto has a magnitude of a bit more than +14m. The Full Moon has a visual brightness of about -12m.55.

Marking character
Single, printable characters which lead and trail the output text for marking purposes.

Mean Earth equator radius
The mean radius of Earth at the equator is about 6,378.137 kilometer.

Mean solar time
Mean solar day
Mean sun
A star day is also known as a mean solar day. Because the Sun apparently shifts with respect to the vernal equinox point on the ecliptic due to the Earth's orbit around the Sun, the star day and the true solar day have a different length. As the true Sun namely moves irregularly through the ecliptic, a fictitious mean Sun with a symmetrical motion through the celestial equator is used for deriving the mean solar time.

Meridian
Either a geographical longitude or an astronomical vertical circle.

Metacharacters
Regular expression operators
Special characters in a regular expression.

Midnight height
The elevation of a celestial body as it happen at astronomical midnight time of the celestial body.

Midnight phase angle
The phase angle of a celestial body as it happen at astronomical midnight time of the celestial body.

Modifier
One or more characters which directly trail a short-style option, and which define a special mode of operation for this option.

Morning width
Rise width
The horizontal angular distance between the rise azimuth of a celestial body and the East direction.

Nautical twilight
The time when the center of the Sun passes a reference altitude of 12 degrees below a mathematical horizon.

Negated character list
Complemented character list
Matches any one of the characters, except those in the square brackets, in a text, that is processed by a regular expression.

Negative day
Those days in the biorhythm in which one or more of the biological cycles have a negative maximum value. At that time, one's system is said to be in a lessen state.

Noon height
The elevation of a celestial body as it happen at astronomical noon time of the celestial body.

Noon line
The straight line which connects the North and the South point.

Noon phase angle
The phase angle of a celestial body as it happen at astronomical noon time of the celestial body.

Octal system
Base-eight notation, where the digits are 0...7.

Opposition
The Earth is in one line between the celestial body and the Sun, and therefore, the celestial body is completely visible from the Earth. In terms of the Moon, this is the Full Moon phase.

Option
A special type of command line argument which controls how Gcal behaves.

Orthodrome
A great circles arc that is casted between two points on a surface of a sphere. Is the shortest geodetic connecting line between two points on a sphere.

Pattern
A pattern is an arbitrary conditional expression against which input is tested. If the condition is satisfied, the pattern is said to match the input. A typical pattern might compare the input against a regular expression.

Phase angle
The phase angle states the phase of a celestial body, i.e. the illuminated fraction of it as it can be seen from the Earth.

Pipelining
The output of a program is used as an input data stream for another program.

Positive day
Those days in the biorhythm in which one or more of the biological cycles have a positive maximum value. At that time, one's system is said to be in a raised state.

POSIX
The name for a series of standards being developed by the IEEE that specify a Portable Operating System interface. The IX denotes the Unix heritage of these standards.

Proleptic calendar mode
This means, Gcal only uses a definite calendar system during a definite period, although there was a change to another calendar system in the historic reality during this definite period.

Rational number
Floating Point number
This is a number that can have a fractional part.

RFC
RFC is the abbreviation of Request for Comments.

Redirection
The output of a program is sent to another device instead of sending it to the standard output channel.

Refraction
Refraction is an optical phenomenon caused by the Earth's atmosphere, which leads to an apparent raising of the location of a celestial body. The amount of refraction increases with growing air pressure and sinking temperature and vice-versa.

Regexp
Regular expression
A way of describing a set of strings.

Relative time offset value
A time offset value which is related to a base time.

Religious Islamic calendar
The astronomically determined Islamic lunar calendar.

Resource file
A file that essentially contains the fixed date entries.

Response file
A file used by Gcal to preload options and commands at program start-up. A response file may contain options and commands, but no references to further response files.

Right ascension
The horizontal angular distance between the center of a celestial body and the hour circle that passes through the vernal equinox point on the ecliptic.

Rise azimuth
The azimuth of a celestial body as it happen at rise time of the celestial body.

Rise height
The elevation of a celestial body as it happen at rise time of the celestial body.

Rise phase angle
The phase angle of a celestial body as it happen at rise time of the celestial body.

Set azimuth
The azimuth of a celestial body as it happen at set time of the celestial body.

Set height
The elevation of a celestial body as it happen at set time of the celestial body.

Set phase angle
The apparent phase angle of a celestial body as it happen at set time of the celestial body.

Shell
The command processor of the operating system. This operating system program interprets and runs given command lines.

Short-style option
The traditional --standard-- style to write an option, e.g. `-x'.

Simple file name
A name that denotes a file, whose access-path either does not start from the root file directory or from the actual file directory, like `file' or `bar/file'.

Simple language code information
A language code that consists of two-letters like de for the German language, as it is defined in the ISO-639:1988.

Single command
3-Month mode command
Produce only one calendar sheet per program run.

Solar Arctic Circle
The geographical latitude circle that is between about 66.7 and 65.9 (corrected for atmospheric refraction) decimal degrees, and the geographical pole. For computing the different twilight phases, this latitude circle decreases to about:

Special text
A text in a Gcal resource file which is started by a `%' character and whose purpose is to suppress output of fixed dates in definite cases, either, or to provide them with particular texts respectively to start external commands.

Summer point on the ecliptic
Summer solstice
Solstice in summer
The Sun's orbit crosses the highest point above the celestial equator that is passed during a revolution of the Earth around the Sun.

Standard week number
The week starts on the respective starting day of the week, and the days in a new year that are preceding the first starting day of the week are in the last week of the previous year, respectively in week zero of the new year.

Star day
The period between two consecutive upper culminations of the vernal equinox point on the ecliptic in the meridian of the observer's location.

Starting date
A part of a Gcal special text that defines the first or earliest date at which the fixed date may occur.

Statute mile
A linear measure, one statute mile is equal to 1.609344 kilometer.

String
A chain of characters.

Switch character
An option is defined by a leading switch character, either the `-' or the `/' character for traditional short-style options, or `--' for mnemonic long-style options; a command may not have a leading switch character.

Text part
That part of a Gcal resource file line that contains the fixed date text.

Topocentric data
Observations of celestial bodies that are done from the surface of the Earth yield in topocentrically based values.

True solar time
True solar day
A true solar day is the period between two consecutive lower culminations of the Sun. This entity is taken as the base for deriving the true solar time (as it is also shown by a sundial during the day).

True track
Course angle
The course angle gives the direction, which is the vertex of a great circles arc (Orthodrome) that is casted between two points on a surface of a sphere, at a meridian (Gcal uses a geoid (rotation ellipsoid) that is calculated taking pattern from the World Geodetic System, short W.G.S, that was designed in 1961). Such an arc is the shortest geodetic connecting line between two points on a sphere. Indeed, the course angles on such an arc are changing continually, because the circular line that is casted intersects each meridian with another angle -- except the case, that both co-ordinates are referring to exactly the same longitude or to exactly the same latitude.

Twilight
The interval of time before sunrise and again after sunset, during which natural light is provided by the upper atmosphere that does receive direct sunlight and reflects parts of it towards the Earth's surface.

Unix
A computer operating system originally developed in the early 1970's at AT&T Bell Laboratories. It initially became popular in universities around the world, and later moved into commercial environments as a software development system and network server system. There are many commercial versions of Unix, as well as several work-alike systems whose source code is freely available (such as Linux, NetBSD, and FreeBSD).

Vernal equinox point on the ecliptic
The point where the ascending Sun's orbit intersects the celestial equator.

Whitespace character
For example Tab, Space, Form-feed and similar characters.

Winter point on the ecliptic
Winter solstice
Solstice in winter
The Sun's orbit crosses the lowest point below the celestial equator that is passed during a revolution of the Earth around the Sun.

Word
A sequence of one or more letters, digits, or underscores (`_') in a regular expression.

Zuhr prayer time
The second Islamic prayer time. Begins after the astronomical noon time of the Sun, and ends at the beginning of the Asr prayer time.


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