Season of the Inundation, first of three seasons in the civil calendar, associated with the rising of the Nile. The flooded Nile brought important nutrients and fertilization to surrounding farmland, originally marking the beginning of the Egyptian civil year. However, as the solar calendar became increasingly less aligned with the civil calendar Akhet lost association with the behaviour of the Nile and seasonal changes in general.

Altitude (Alt) is a measure of the angle between a point of interest and the observer's local horizon. The horizon has an altitude of 0° and the zenith 90°. One of two coordinates in the horizontal coordinate system, the other being Azimuth.

A small group of stars. Asterisms may be a subset or a superset of constellations. Stars in an asterism may also belong to different constellations. Some or all decans may be asterisms rather than single stars.

astronomical diagram
A type of ancient Egyptian decoration, found on temple and tomb ceilings and on the outer surface of water-clocks. Most examples are from the New Kingdom (19th dynasty) through to the Late Period and Greco-Roman times. Astronomical diagrams contain different combinations of various elements, including (but not limited to) representations of circumpolar constellations, decans and planets. Each element may also be shown with their associated deities.

astronomical texts
A general term for any writing which deals with astronomical topics. These include parts of extended bodies of literature, for example the Pyramid Texts and Coffin Texts (diagonal star tables), works with astronomy as a major focus such as the Ramesside star clock and the Book of Nut (Fundamentals of the Course of the Stars), and miscellaneous texts which deal with astronomical observations, explanations pertaining to astronomical phenomena, or biographies on astronomical practices.

Capital of Nome XIII of Upper Egypt located on the west bank of the Nile. Special attention was paid to the description of the tombs of Asyut during Napoleon’s expedition. Asyut is the provenance of most known diagonal star table coffin texts. The modern-day city with the same name is located nearby.

Azimuth (Az) is a measure of angle around the horizon to a point of interest. The usual convention is to measure angle clockwise from north, which has azimuth 0°, towards east, which has azimuth 90°, south 180°, and west 270°. One of the two coordinates in the horizontal coordinate system, the other being altitude.

Coffin lids are constructed with long planks of wood laid side-by-side. Battens, or cross braces, are smaller pieces of wood fixed across the planks with the purpose of securing the planks together. There are usually two or three battens per lid. Coffin lids are smooth on top, so the battens appear on the inside face of the lid. As such, battens are often incorporated into the diagonal star table interior design of the lid. This often results in the first column of the table being painted over the first batten and the last column on the last batten.

Book of Nut
An example of funerary literature first appearing in the New Kingdom, the vignette heading this book is found only in the Osireion and tomb of Ramses IV. Nut, the sky goddess, arches over the scene and is supported by Shu, the personification of air. Nut is depicted swallowing the Sun at the start of the night, which then travels through her body, and rises at her feet in the morning. The vignette is followed by texts dealing with timekeeping and the motion of the stars. Part of the text survive in later versions, including annotated copies on papyrus from as late as the 2nd century AD.

ceiling of Senenmut
The ceiling of the tomb of Senenmut, located at the site Deir el-Bahari in Luxor, is decorated with the oldest surviving Egyptian astronomical diagram. The diagram is separated into two sections, northern and southern. The northern section contains depictions of northern constellations and the twelve months of the lunar calendar. The southern section contains a list of decans and planets visible to the naked eye, with Mars omitted.

celestial equator
Related to the Earth's axial tilt, the celestial equator is given by the plane perpendicular to the Earth's axis. The great circle on the celestial sphere intersecting this plane, the same plane as Earth's equator, is known as the celestial equator. Objects located on the celestial equator are theoretically visible from anywhere on Earth at some point during the year.

A star or constellation that is close to one of the celestial poles such that from the observer's perspective it never sets below the horizon. The part of the sky for which this is true depends on the latitude of the observer. For example, for an observer in Cairo (latitude = 30.05 degs N), any celestial object that is within a radius of 30.05 degs of the North Celestial Pole will never set below the horizon. This does not take into account local horizon effects, which will decrease this radius.

civil month
A 30-day period of the Egyptian civil year. Each civil month is composed of three decades. There are four civil months in each season.

civil year
Divided into three seasons - akhet, peret, and shemu - each consisting of four, 30-day months. In addition to these 360 days, an additional five extra days were added to the year. These extra days, called epagomenal days, served to reconcile the civil calendar with the astronomical year. Despite the addition of the epagomenal days, the civil year still did not account for the quarter day reminder in a solar year. As a result, the civil calendar shifted at a rate of one day every four years compared to the solar year.

Ancient Egyptian coffins are usually wooden receptacles (as opposed to stone sarcophagi) in which the deceased is placed, after mummification in some cases. The coffins may: be rectangular or anthropoid; be nested; have various decorations. These decorations can help determine the location and date of production. A small number (<30) of coffin lids have diagonal star tables. All of the coffin lids with tables are on rectangular wooden coffins, and only seem to occur on the lids of inner coffins in sets or in single coffins which are not parts of sets.

Coffin Texts
The Coffin Texts are a category of ancient Egyptian texts used from the Middle Kingdom onwards. They acted as funerary spells, written on coffins and other funerary objects. Coffin Texts were preceded by the Pyramid Texts, which were exclusively used by royalty. The use of Coffin Texts by commoners represented a democratized afterlife. Unlike the earlier Pyramid texts, which are related to the afterlife in the celestial realm associated with pharaohs and gods, Coffin Texts are associated with subterranean afterlife in Duat, ruled by Osiris. Coffin Texts feature themes such as judgement by Osiris and contain spells to protect the deceased against the dangers of this afterlife.

A set of stars or asterisms that are associated through a pattern in the Earth's night sky. This pattern is formed by prominent stars with apparent proximity to each other in the celestial sphere. The proximity of stars within constellations on the celestial sphere is unrelated to their actual proximity in space.

Culmination occurs when a star or other celestial body transits the meridian (i.e., reaches its highest altitude above an observer's horizon). At the time of culmination, by definition, a star is due north or due south of the observer. The culmination of the Sun each day marks local noon.

date row
Present in some diagonal star tables, omitted in others, the date row appears above the first row of the ideal diagonal star table. From right to left, the date row begins with the first decade of the first month of the first season (Akhet). The row continues through the decades until reaching the 36th decade, the last decade of the fourth month of the third season (Shemu). Following the 36th decade are the four list columns, including one for the epagomenal days. Occasionally a header for these columns can be found included in the date row.

Ten-day period of the civil calendar. In diagonal star tables, a single column corresponds to a decade.

A decan is a significant star or asterism observed and recorded by ancient Egyptian astronomers. In Egyptian astronomical texts, decans are named and later became associated with decanal deities. The behaviour of decans in the night sky was observed and depicted in diagonal star tables, where they are named in the cells of the tables. Although we can translate many names of decans, it is unclear in most cases to which modern-day star(s) they actually refer.

decan list
A decan list is an ordered list of names of decans (stars or asterisms) which is characteristic of either a single astronomical text or of a family of texts sharing similar decanal features.

decanal belt
Notional region of the sky containing the decans. Located south of the ecliptic, the belt contains Sirius and stars in the region of Orion. The distinguishing property of stars and asterisms located in the decanal belt is that their period of invisibility ideally corresponded to that of Sirius, 70 days.

decanal deity
Deities which are associated with decans. The relationship between deities and decans is not injective (one-to-one). The deities are named and sometimes depicted in astronomical diagrams from the New Kingdom onwards.

decanal hour
A decanal hour is notional unit of time representing a twelfth part of the night, useful in discussing diagonal star tables. In the model of diagonal star tables as clocks, each row of the table represents one decanal hour. Unlike a modern-day hour, a decanal hour does not have a fixed length.

One of the two directional coordinates (the other is right ascension) for a point in the celestial sphere given by the equatorial coordinate system. Declination is comparable to the terrestrial measurement of latitude. It is measured in degrees north (positive angle up to +90°) or south (negative angle down to -90°) of the celestial equator. The celestial equator itself is therefore the line of 0° declination and the north celestial pole has declination of +90° .

There were many gods and goddesses recognized throughout ancient Egyptian civilization, and their identities, representations, functions, statuses, and relationships were fluid over time. Deities could move from being local to being national figures, could merge, and change their familial relationships and spheres of influence. Some foreign deities were incorporated into the Egyptian pantheon. Many deities were associated with certain animals, and were therefore sometimes depicted as that animal or as having the head of their representative animal.

deities of the epact
The eleven deities that represent the eleven days of the difference in length between the solar year and the lunar year. These include the deities after which the five epagomenal days are named (Osiris, Horus, Seth, Isis and Nephthys), with another six deities inserted before, after and between each epagomenal deity.

diagonal star calendar
Alternative term for diagonal star table. The label 'calendar' is problematic, however, because it encourages assumptions regarding the intended function of the tables. As such, diagonal star table is the prefered term.

diagonal star clock
Alternative term for diagonal star table. The label 'clock' is problematic, however, because it encourages assumptions that the intended function of the tables for the purpose of timekeeping. As such, diagonal star table is the prefered term.

diagonal star table
Diagonal star tables are funerary texts painted on the inner face of early Middle Kingdom coffin lids (with the single notable exception of the table on the ceiling of the New Kingdom Osireion at Abydos). The tables are in the form of a grid containing in each cell the names of individual decans. Each column of the table lists the decans visible throughout a night. Each column represents a 10-day period (a decade). There are forty columns in an ideal diagonal star table: one for each of the 36 decades of the Egyptian civil year, three listing the 36 ordinary decans, and one for the epagomenal days (which lists the triangle decans). Other features of diagonal star tables are an offering formula written along a horizontal band, depictions of four deities in a vertical band, and (often) a row of dates along the top.

A series of rulers (kings or pharaohs) usually, but not necessarily, of the same lineage. These groupings would not have been recognized at the time, but were imposed by later scholars as convenient ways to refer to time periods. Standard chronologies include around 34 dynasties from the pre-dyanastic period (31st century BC, 0th dynasty) to the Greco-Roman period (4th century BC, 33rd dynasty, more commonly referred to as "the Ptolemaic dynasty" which ended with Cleopatra VII and her offspring).

The apparent path of the Sun on the celestial sphere. The ecliptic, at the centre of a band known as the zodiac, follows a great circle centred on the Earth. The ecliptic plane is coplanar with the orbit of the Earth around the Sun.

Egyptian Astronomical Texts
The field of ancient Egyptian astronomy is dominated by the works of Otto Neugebauer and Richard Parker in their three-volume work on the subject, published in 1960, 1966 and 1969. The first volume focusses on diagonal star tables, decans, and the Book of Nut, the second volume on Ramesside star clocks, and the third on astronomical diagrams and other astronomical texts. It remains an essential reference in the field but is now outdated and inaccessible.

epagomenal column
The fourth and final list column on diagonal star tables, the column represents the decans during the five intercalation days. These extra days were inserted to the ancient Egyptian civil calendar, without which would only be composed of 360 days, so that it more accurately followed the solar year. The calendar and solar year were still approximately one quarter day out of synchronization, as the ancient Egyptians did not use leap days.

epagomenal day
The ancient Egyptian civil year was divided into twelve months each consisting of 30 days. To reconcile (approximately) the 360 days of the civil year with the 365.25 days of the solar year, an additional 5 days were added to the calendar. These days, called epagomenal days, existed outside the standard months. They were later given religious significance and incorporated into the creation myths of the children of Nut. The epagomenal days are depicted on diagonal star tables in the fourth and final list column.

Two times during the year when the celestial equator (the projection of the Earth's equator) intersects with the ecliptic (the apparent annual path of the Sun across the sky). At these times, the length of the day is approximately equal to the length of night. Equinox can also refer to the day on which these times occur. Currently, the vernal or spring equinox occurs on 20 March and the autumnal equinox occurs on the 22 or 23 September.

The Foreleg of an Ox, called Meskhetiu in Egyptian, is a representation of the asterism we know today as the Plough or the Big Dipper. In diagonal star tables it is illustrated in the vertical band.  In astronomical representations, it is depicted in the northern circumpolar group as an ox or a foreleg of an ox.

four winds
The four winds correspond to the cardinal directions, and the associated deities may also be personified. They are sometimes depicted within later astronomical diagrams.

heliacal rise
Heliacal rise occurs when a celestial body (star, constellation, moon, or planet) rises over the eastern horizon at dawn for the first time after a period of invisibility. In the days following the heliacal rise, the body will rise progressively earlier before dawn as the apparent distance between it and the Sun increases. This increasing separation will eventually result in the body rising at sunset. After this point, it will set in the west before dawn, having increasingly shorter time in the night sky after sunset. Eventually, the celestial body will be unobservable at night, until its next heliacal rise.

heliacal set
Heliacal set is the act of a celestial body (star, constellation, moon, or planet) disappearing below the horizon in the night sky for the last time closely after sunset. After heliacal set, the body no longer appears in the night sky for a period of time until it undergoes its next heliacal rise. During the period of invisibility following heliacal set, the body will be only be above the horizon at approximately the same time as the Sun.

The contour which divides the ground from the sky. The true horizon is what would be seen if there were no obstructions present (obstructions such as hills, trees, buildings, etc.); the visible horizon is what is actually seen. With different horizons, alignments and timings of astronomically significant events will vary from location to location. In Egyptian religion, the horizon was a liminal region: a gateway to the underworld (western horizon) and a locus of rebirth (eastern horizon).

horizontal strip
On diagonal star tables, the horizontal strip runs lengthwise across the table dividing the table into upper and lower halves. On the ideal table the strip is located between the 6th and 7th hour rows. The horizontal strip often begins with a large, red disk, followed by funerary offering texts to Re, the four deities in the vertical strip, and selected decans.

Divisions of the day and night each into twelve parts, totalling twenty-four hours. The ancient Egyptian definition of hour differs from the modern definition as the length of their hour differed between night and day, depended on the instrument of measurement, and fluctuated with the seasons. For example, depending on the time of year, the twelve divisions of the night may be longer or shorter than the twelve divisions of the day.

imperishable star
The ancient Egyptian term for the circumpolar stars (the stars which, for a given latitude of observation, never set).

inferior planet
A planet whose orbit is inside that of the another planet. Most commonly, this term is used for Earth's inferior planets, Mercury and Venus. The opposite of inferior planet is superior planet. The ancient Egyptians separated these two groups of planets, presumably based on their different movements relative to the Sun and stars.

list column
On an ideal diagonal star table, there are 36 columns each representing a ten-day period, followed by four columns called the list columns. The first three list columns simply repeat the names of all 36 ordinary decans in order. This is equivalent to repeating the columns that are used during the start of each of the three ancient Egyptian seasons. The fourth list column is used during the final five days of the year, and is composed of triangle decans. Only four extant diagonal star tables are complete enough to include any list columns: T1, T6, T7 and T8.

lunar staircase
A symbolic set of fourteen steps that represent the fourteen days of the waxing Moon just prior to a Full Moon. Each step has a deity associated with it. Examples occur at the temples in Edfu and Dendera.

In modern astronomy, magnitude is a measure of the brightness of a celestial object such that an object with a larger number is a fainter object. The scale is logarithmic and is such that magnitude 6 object is 100 times fainter than a magnitude 1 star. In ancient astronomy, namely by the Greek astronomers Ptolemy and Hipparchus, the brightness of stars was perceived as an indication of their size. We know now that the magnitude depends on the intrinsic temperature of and the distance to the star.

A meridian is a great circle on the celestial sphere which passes through the celestial north and south poles and the observer's zenith. The line of this great circle is divided into two halves, both of which terminate at the poles: the local meridian, containing the zenith, and the antimeridian, containing the nadir.

Meskhetiu was the name given to the asterism known today as the Plough or the Big Dipper. This asterism often appears on ancient Egyptian astronomical texts depicted as the Foreleg of an Ox. It occurs on diagonal star tables, illustrated on the vertical band and often named in the offering formula along the horizontal strip.

Middle Kingdom
Period of ancient Egyptian history between 21st and 18th centuries BCE. The Middle Kingdom spanned the second half of the 11th and 12th dynasties.

New Kingdom
A period of ancient Egyptian history between the 16th and 11th centuries BCE. The New Kingdom spanned the 18th, 19th, and 20th dynasties.

offering text
The offering text is a funerary text believed to allow the deceased to make offerings to deities via the intercession of the king. It is commonly found on many kinds of funerary objects. The offering text appearing on the horizontal strip of diagonal star tables follows a unique pattern. The deities include Re, the four deities of the vertical band (Nut, the Foreleg of an Ox, Orion, and Sothis), and a subset of the decans.

Old Kingdom
A period of ancient Egyptian history between the 27th and 22nd centuries BCE. The Old Kingdom spanned the 3rd to the 6th dynasties.

ordinary decan
Ordinary decans found on diagonal star tables account for most of the decans in the main body of the table. On the idealised table the ordinary decans are represented by the numbered decans 1 to 36. In the list columns on the left side of diagonal star tables, the ordinary decans are listed in the first three list columns. In contrast, the lettered decans listed in the fourth list column are called triangle decans.

Orion is a constellation known to the Greeks and still in use today. It is highly likely that Orion corresponds approximately to the Egyptian constellation Sah or Sahu. Sah/Orion is the stellar manifestation of the god Osiris. In diagonal star tables, Orion is illustrated as a deity in the vertical strip. He is pictured holding the was-scepter and the ankh-sign.

Located behind the temple of Seti I at Abydos, the Osireion is a funerary complex decorated in the style of a Valley of the Kings' tomb from the 18th dynasty. There are two astronomically significant ceilings which include observations of daily and annual celestial motions, records of heliacal rising and disappearance for some revered stars, instructions for the construction of a sundial, and images from the Book of Nut (also known as The Fundamentals of the Course of the Stars). Further, the ceiling of the Osireion is decorated with the only known diagonal star table not found on a coffin lid. The Osireion is often partially submerged with water from the local water table, preventing general access.

Season of Emergence, second season in the civil calendar, associated with the retreat of the Nile. Ebbing of the Nile from farmland exposed nutrient-rich soil ideal for planting crops, originally making Peret the ancient Egyptian growing season. However, as the solar calendar became increasingly less aligned with the civil calendar Peret lost association with the behaviour of the Nile, and seasonal changes in general.

Precession refers to the continuous change in the orientation of the Earth's rotational axis. After approximately 26,000 years, or one Platonic year, the Earth's axis will precess such that it traces out a complete circle. Precession is significant to the discussion of ancient Egyptian astronomy because it changes the apparent position of stars in the night sky over time relative to an observer on Earth. In particular, the North Celestial Pole was located closer to the star Thuban in the constellation of Draco during ancient Egyptian times, rather than Polaris in Ursa Minor as it is today.

Ramesside star clock
These star clocks are so called because they appear in various tombs found in the Valley of the Kings from the Ramesside period: Ramses V / VI, VII and IX. Each clock has two tables per month (24 tables for the whole year), and each table has a kneeling figure who faces out from the table. The vertical lines of the table represent the lines that would pass through the heart, and the left and right eyes, ears and shoulders of the figure, with which the alignment of the stars in the sky are then compared. The horizontal lines of the table separate the start and/or of the hours of the night.

right ascension
Right ascension measures the angular distance along the celestial equator eastward from the vernal equinox to the hour circle of the point of interest. Right ascension is comparable to the terrestrial measurement of longitude. One of the two directional coordinates for a point in the celestial sphere given by the equatorial coordinate system.The other coordinate direction is declination.

Sah or Sahu
It is highly likely that Sah or Sahu corresponds to the modern constellation Orion. Sah/Orion is the stellar manifestation of the god Osiris. In diagonal star tables, Sah is illustrated as a deity in the vertical strip. He is pictured holding the was-scepter and the ankh-sign.

seasonal hour
Seasonal hours are measurements of time which depend on the length of day and night. Often produced by dividing the day and night each into twelve equal parts, the seasonal hour is then dependant on the time of year. This definition differs from our modern understanding of hour as there is no fixed quantity of time associated with the seasonal hour.

Season of Harvest, third season in the civil calendar, during which grain crops are harvested. Shemu, literally ‘low water’, was originally the Egyptian dry season or summer. However, as the solar calendar became increasingly less aligned with the civil calendar Shemu lost association with the behaviour of the Nile, and seasonal changes in general.

sidereal time
A time scale using the Earth's rate of rotation measured relative to the distant stars. The sidereal day is approximately four minutes shorter than a solar day, with sidereal hours, minutes, and seconds proportionately shorter. Used by astronomers because, from a fixed location of observation, a star located at one point in the sky will be found at approximately the same location another night at the same sidereal time.

Sigla (sing. siglum) are abbreviations for the provenance and current location used to identify ancient Egyptian coffins.

Brightest star in the night sky. Stellar counterpart of the goddess Sopdet/Sothis. The helical rising of Sirius preceded the rising of the Nile, acting as the base to the civil calendar. The helical rising of Sirius marked the beginning of the season of inundation (Akhet), the first season of the civil calendar.

solar year
A solar year is the period of time required for the Earth to make one complete orbit around the Sun. The length of this period is approximately 365.242 days. In ancient Egyptian astronomy, the solar year was approximated with the observance of a civil calendar containing 36 ten-day decades and the later addition of five days, called epagomenal days. The civil year, with a total of 365 days, became misaligned from the solar year by roughly one day every four years.

Two days of the year on which several features related to the Sun reach extreme values. At the summer solstice, in the Northern hemisphere outside of the tropics, the Sun reaches the highest point above the horizon at noon, it rises at a point most north of east and sets most north of west, and it is the longest day. Conversely, at the winter solstice the Sun reaches the lowest point at noon, it rises at a point most south of each and sets most south of west, and it is the shortest day. Currently, the summer solstice occurs on 20 or 21 June, and the winter solstice occurs on 21 or 22 December.

Deification of the star Sirius. Sopdet is consort to Sah, and a stellar manifestation of the goddess Isis. Sopdet is illustrated on the vertical band of diagonal star tables.

Greek translation of Sopdet, the deity associated with the star Sirius. Sopdet is paired with Sah, and is a stellar manifestation of the goddess Isis. Sopdet is illustrated on the vertical strip of diagonal star tables.

At Egypt's latitude, sunrise occurs more swiftly than at northern latitudes. This is significant to ancient Egyptian culture, as the quick change from night to day is related to the birth of the Sun, an important religious tradition. In ancient Egyptian astronomy, a quickly occurring sunrise leaves less time for twilight, which potentially allowed observers to end the twelve decanal hours of the night shortly before sunrise.

At Egypt's latitude, sunset occurs more swiftly than at northern latitudes. This is significant to ancient Egyptian culture, as the quick change from night to day is related to the "swallowing" of the Sun by the sky goddess Nut. In ancient Egyptian astronomy, a quickly occurring sunset leaves less time for twilight, which potentially allowed observers to begin the twelve decanal hours of the night shortly after sunset.

superior planet
A planet whose orbit is outside that of the another planet. Most commonly, we consider Earth's superior planets, Mars through to Neptune. The ancient Egyptians were only aware of the three superior planets that are visible to the naked eye: Mars, Jupiter and Saturn. The opposite of superior planet is inferior planet. The ancient Egyptians separated these two groups of planets, presumably based on their different movements relative to the Sun and stars.

T & K families
Surviving specimens of diagonal star tables can all be categorized into one of two families based on the decans occurring in the top right corner of the table. Tables beginning with TmAt decans (TmAt Hrt and TmAt Xrt) are called 'T tables'. Tables beginning with knmt decans (tpy-a knmt, knmt, etc.) are called 'K tables'.

transit star clock
The transit star clock is a star table included in the Osireion and the tomb of Ramses IV, as part of the Book of Nut. It contains a list of decans similar to those found on diagonal star tables, and describes how the decans move through the sky, and the period of time taken in each section. The decans spend 70 days in Duat, the underworld, 80 days in the eastern sky, 120 days "working", where their work is to mark the start of the hours by transiting the meridian, and 90 days in the western sky after working, before beginning the cycle again.

Conversion of hieroglyphs to Roman alphabet. In order to view all the information on this site, you will need to have a transliteration font installed (see Reference section). Slight variations of transliterated spellings can occur for the same hieroglyph for two reasons: the hieroglyphs themselves occur in a variant order and this variation is maintained during transliteration, or because of slight variations of the transliteration process depending on the individual scholar.

In diagonal star tables, the triangle refers to a triangular area at the lefthand end of the ideal table plus the fourth list column. The first triangle decan apppears at the end of the 26th column, after which a new triangle decan is added every column. All decans within this triangular area are called triangle decans and are denoted by letters A-L in the ideal table. The twelve triangle decans serve as a group during the five epagomenal days.

triangle decan
In the idealised diagonal star table, with decans numbered 1 to 36 and letters A to K, the lettered decans are called triangle decans. The are so called because of the shape they create in the leftmost side of the table. The triangle decans are listed in the fourth list column, called the epagomenal column. Their function as epagomenal decans is to bridge the 5 day gap between the 36th decade and the 1st decade of a new year. In contrast, the numbered decans listed in the first three list columns are called ordinary decans.

The period before sunrise or after sunset, when the Sun is below the horizon but illuminating the upper parts of the Earth's atmosphere which scatters light down to the ground. There are different modern definitions of twilight which are dependent on how far the centre of Sun is below the horizon: astronomical (18°), nautical (12°), and civil (6°). For the ancient Egyptians, the period of twilight would have represented a transitional state of the day.

unwearying stars
This ancient Egyptian term refers those stars that appear to rise in the east and set in the west when viewed from Egypt, in contrast to the "imperishable stars" (circumpolar stars) in the northern part of the sky which never appeared to rise and set.

vertical strip
A filled space between the 18th and 19th decade columns on the ideal diagonal star table. Along this strip are representations of Nut, the Foreleg of an Ox, Orion, and Sothis. The order of these figures in the vertical strip is used by Neugebauer and Parker to distinguish groups of star tables. Descriptive text often accompanies each figure in the strip.

water clock
Water clocks mark the passage of time by the slow transfer of water either into (inflow type water clock) or out of (outflow type water clock) a vessel. Water clocks were used to mark time during the night when sundials could not be used. Water clocks may have been used to establish the hours of a star table. Surviving outflow water clocks were decorated externally with astronomical diagrams. The most complete (and earliest) example is Amenhotep III's alabaster "Karnak water clock" in the Egyptian Museum, Cairo.

The constellations that appear to lie along the ecliptic (the path the Sun appears to traverse through the background stars throughout the year, due to the Earth's motion as it orbits the Sun). These zodiac constellations effectively create a belt in which the Moon and the planets also appear to traverse the celestial sphere. The zodiac appears in ancient Egypt during the Late Period.