The various astronomical periods change over time. The numbers quoted here are around the beginning of the third millenium AD, and the change per century is usually in the last digit or two quoted.
Historically, the movement of the moon across the background of fixed stars was studied, and calendars based on them, before the ideas of solar calendars drifted in, probably ultimately from the region of Sumer. The month was defined as the period from one new moon to the next. Since the moon moves across the fixed stars in a time period of 27 or 28 days (this siderial month is actually 27.321661 days), its zodiacal path in the sky was divided into 27 or 28 parts, and each of these lunar asterisms was named after a prominent star in it, each conceived of as a wife to moon. In this timespan, the earth however shifts in its orbit around the sun, and the period from new moon to new moon is 29 or 30 days (this synodic month is 29.530589 days on average). This results in the asterism in the background of the full moon advance by two or three each month. It thus became convenient to name the month after the background asterism on the full moon night, and these are still the names of the months, even though they are now defined in terms of the position of the sun against the fixed stars (siderial year of 365.256363 days). See the Bengali calendar page for more details.
The names in the solar zodiac show clear external influence, and are from a later period. A few other stars were also named.
The list of these stars or nakSatra (নক্ষত্র; by which one wishes to attain) is very old, but their numbering has changed. Due to the precession of earth's axis of rotation, the vernal equinox (defining the tropical year of 365.24219 days) shifts back by about one nakSatra every 1000 years. It was in mRgashiras (মৃগশিরঃ) in about 4500 BC, in kRttikA (কৃত্তিকা) in 2500 BC, in ashvini (অশ্বিনী) about 500 BC, and is currently in bhadrapada (ভদ্রপদ) (revatI (রেবতী) was closest to the vernal equinox, within 10', in 572 A.D.), and correspondingly, the counting could begin at any of these positions. In fact, the counts from kRttikA (কৃত্তিকা) dominate the early literature, and those from ashvinI (অশ্বিনী) the later ones. Sometimes, it is also counted with sraviSThA (শ্রবিষ্ঠা) as the first. uttara phAlguNI, svAtI, uttarASADh.A, uttara bhadrapada, and revatI (উত্তর ফাল্গুণী, স্বাতী, উত্তরাষাঢ়া, উত্তর ভদ্রপদ, রেবতী) have often been described as ‘fixed’: it is not clear what was intended by that.
This word probably derives from a word meaning ‘to cut’ or one related to ‘cart’. This is represented by a flame or a razor, and it consists of 6 stars which are commonly called the Pleiades in the west. This group of stars has been associated with agni, the god of fire. Alcyone/Alcor (η Taurii) amongst them is called ambA (অম্বা) (meaning ‘mother’) or arundhatI (অরুন্ধতী) (meaning related to ‘not obstructing’). It is the junction star with rohiNI.
The former name is probably derived from a word meaning ‘rise’ or one meaning ‘red’, ‘red cow’, or ‘red deer’, whereas the latter is derived from a root which means ‘to grow’. It is represented by a wheeled vehicle, temple or fish. It lies about 10° south east of Pleiades and consists of the five stars α (Aldebaran, which sometimes is alone called rohiNI), β (sometimes called agni or hutabhuj (অগ্নি, হুতভুক্), both meaning ‘sacrificial fire’), Θ1,2, γ, δ, and ε-Tauri. In the west these comprise the constellation of Hyades. It also includes three stars from Auriga: α (Capella) and δ-Aurigae (called prajApati (প্রজাপতি) meaning ‘lord of the born’). The former is probably the same as the star called brahma-hRdaYa (ব্রহ্মহৃদয়) (meaning the ‘heart’ or ‘inside’ of brahma, the original principle, derived from a word for growth), or aryaman (অর্যমা) (meaning a ‘bosom friend’, one of the important deities, the word being derived from a root meaning to ‘go straight’ or to ‘rise’ usually related to being honourable. Aldebaran is the junction with mRgashIra. Confusingly, jyeSThA is sometimes also called rohiNI
The former means ‘the head of wild game beast’, and the latter is related to ‘beginning of the year’. It is represented by the head of an antelope and consists of the three stars in Orion: λ and φ1,2. λ is the junction star with ArdrA. It is also called mRgashIrSa (মৃগশীর্ষ) (same meaning), andhaka (অন্ধক) (blind), AryikA (আর্যিকা) (honourable woman), and invaka (ইন্বক) (pervading).
The entire constellation of orion was originally pictured as prajApati (প্রজাপতি) (meaning ‘lord of creatures’) in the form of a mRga (মৃগ) (meaning ‘game animal’; α or Betelgeuze which forms the left forearm and therefore called bAhu (বাহু), β or Rigel, γ or Bellatrix also called bAhu, and κ forming the legs and feet of the animal) going after his daughter rohiNI (the previous asterism; sometimes uSas (উষা), the morning or evening light appears instead). The nearby mRgavyAdha (মৃগব্যাধ) (meaning ‘hunter of game animal’, called Sirius in the west) stopped him with an arrow (iSus trikANDa (ইষুস্ত্রিকাণ্ড), meaning ‘arrow in three pieces’, identified with the belt of orion consisiting of δ, ε, ζ). This arrow is now also considered part of the asterism. A human concept of prajapati is in the description of hastA to anurAdhA below.
The word is related to ‘wet’, and the asterism is represented by a gem. It is presided over by the deity rudra (রুদ্র) (probably meaning ‘roaring’). The main star here is α-Orionis or Betelgeuze, also called bAhu (বাহু).
These words are the dual forms meaning ‘restoring good’ and a word related to ‘twins’ respectively. This asterism is presided over by aditi and consists of α and β-Geminii, which are called castor and pollux respectively in the west. β forms the junction with the next puSYA
These words mean ‘nourishment’ or ‘flower’, ‘prosperous’ or ‘auspicious’, ‘auspicious’ or a heavenly archer respectively. This asterism is presided over by the deity bRhaSpati (বৃহষ্পতি) (‘big lord’). They consist of the asini γ and δ, θ, praesaepe-Cancrii. δ forms the junction with AshleSA.
These words are related in meaning to ‘embrace’ and the asterism is represented by a wheel or by serpents. It coincides with what is called Hydra in the west. ε forms the junction with maghA.
This word is related to the meanings ‘gift’, ‘mighty’, or ‘generous’, and the asterism is often represented by a wheel. It is presided over by the deity pitaras (পিতরঃ) (meaning forefathers or parents). Consisting of α, γ, and ζ, it comprises the sickle of Leo. α is the junction star with pUrva phAlgunI.
This is the former (pUrva (পূর্ব) ) of a double asterism called phAlgunI (ফাল্গুনী) which word is related to words for ‘red’ or ‘evil’. These asterisms are represented by fig trees, or as a bed when they are considered together. It is presided over by the deity Aditya (আদিত্য) (sons of aditi (অদিতি), the free) aryaman (অর্যমা) (bosom friend, derived from a word for go straight or honourable). It consists of δ and θ in Leo, the former being the junction with uttara phAlgunI.
This is the latter, or uttara (উত্তর), of the double asterism described above. It consists of β or Denebola and Fl. 93 (or a star in coma berenices) in Leo, the former being the junction with hastA.
This word meaning ‘hand’ was viewed as a hand of the huge figure of prajApati (প্রজাপতি) (‘lord of the born’; see the description of asterisms till anurAdhA in the sky, and is presided over by savitR (সবিতা) (meaning ‘the stimulator’, i.e. the sun). It consists of α, β, γ, δ, and ε-Corvi, δ being the junction with citrA.
The word is related to the meanings ‘conspicuous’ or ‘bright’, and the asterism is represente by a lamp or a pearl. It is visualized as the head of prajApati (see under hastA above) and is presided over by the deity tvaSTR (ত্বষ্টা) (fabricator). It consists of α (spica) Virginis.
These words are related to the meanings ‘fixed’ or ‘good goer’ or ‘sword’ and ‘an outcast’ respectively. It is represented by a coral bead, gem, or pearl. It is visualized as the heart of the figure of prajApati (see under hastA above). It consists of α Boötes or Arctaurus which may have been called AryamaNa (আর্যমণ) (related to a word for a deity aryaman (অর্যমা) meaning ‘bosom friend’, a word derived from the root meaning ‘to go straight or honourably’).
The first of these words means ‘branched’ and the second is related to a word for ‘gift’ or ‘prosperity’. It is represented by a decorated arch It is visualized as the thighs of prajApati (see under hastA above), and is presided over by the deities indra (ইন্দ্র) (probably related to a word meaning ‘to drop’) and agni (অগ্নি) (fire). This asterism originally consisted of α1,2 and β-Librae, but was later enlarged to include γ and ι, and probably also σ-Librae and δ-Scorpii. ι-Librae is the junction star with anurAdhA.
The word means that it follows the previous asterism rAdhA (রাধা) and it is usually represented by a row or line of oblations. It is visualized as prajApati's (see under hastA above) standing place and is presided over by the deity mitra (মিত্র) (meaning ‘friend’). It consists of β, δ, and π, and may also include ν and ρ-Scorpii.
This asterism is not to be confused with the one more commonly called rohiNI described above. The meaning of its primary name is ‘eldest’, and it is represented by an ear jewel It is presided over by the deity indra (ইন্দ্র) (meaning probably related to the word for ‘to drop’). It consists of α (Antares), σ, and τ-Scorpii.
This words means ‘root’. This asterism is presided over by the deity nirRti (নিরৃতি) (a word related to ‘destruction’). It consists of ε, μ, ζ, η, θ, ι, κ, υ, and, possibly, λ-Scorpii.
It is the former, or pUrva (পূর্ব) of the asterisms called ASADh.A (আষাঢ়া) (‘invincible’). These are represented by elephant's tusk separately, or by a bed together. They are presided over by the deity Apas (অপঃ) (water) or vishve devA (বিশ্বেদেবা) (all the bright ones). It consists of γ, δ, ε, η, μ1,2, σ, ζ, φ, χ, and τ-Sagittarii.
This is the latter of the two ASADh.A (আষাঢ়া) asterism as described above. It consists of π, τ, ν, ψ, ω, α, and ζ-Sagittarii.
This word means ‘victorious’ and the asterism was represented by a triangle or a cringata plant. It consists of α or Wega, ε, and ζ-Lyrae, of which the first forms a junction with shravaNA. This asterism is omitted if only 27 nakSatras are counted.
These words mean ‘ear’, ‘lame’, or ‘fig tree’ respectively. It is represented by three footsteps or a trident. It consists of α, β, and γ-Aquilae.
These words mean ‘most famous’ or ‘richest’ respectively. It is represented by a drum or tabor and is presided over by the vasus (বসুঃ) (meaning the bright ones). It consists of α, β, γ, δ, and ε-Delphini (called shishumAra or simshUmAra (শিশুমার, শিংশুমার), words meaning ‘the gangetic porpoise’; the first of these words seems to mean ‘killer of babies’, but since the latter is found even in the earliest texts in India, the derivation ought to be considered uncertain). β, among these, forms the junction with shatabhiSak.
The word means ‘requiring hundred physicians’ and the asterism is presided over by varuNa (বরুণ) (related to words meaning ‘to envelop’, sky god of old, sea god in later mythology). It consists of the 100 stars surrounding λ-Aquarii.
These words refer to the former, or pUrva (পূর্ব), of the two asterisms. The base words mean ‘auspicious feet’ and ‘footstool’ or ‘carpfeet’ or ‘oxfeet’, respectively. They are individually represented as the bifaced ones or twins and together as a couch. They are presided over by aja ekapAd (অজএকপাদ্) (the ‘one-footed or lame driver’) and ahirbudhnya (অহির্বুধ্ন্য) (‘the serpent of the depths’). It consists of α, β, and γ (called indra) Pegasi, the first of which is the junction with uttara bhadrapada.
This is the latter of the asterisms described above. It consists of α, δ, and ε-Pegasi.
The word means ‘wealthy’. It consists of the 32 stars from ζ-Piscium, the first of which is the junction star with ashvinI.
This star was within 10' of the vernal equinox in 572.
The first word means a ‘female horse’ or ‘a horse rider’, the rest are the dual forms. It is represented by the head of a horse, and consists of β and &gamma, and sometimes α-Arietis. β forms the junction with bharaNI.
The first two words, which are singular and plural, are derived from a word for ‘to bear’, and probably mean ‘womb’. The latter seems to be related to the sense of carrying away. The asterism is represented by the pudendum muliebre, and consists of Fl. 41, 33, 35, and 39 in Aries, these comprising the northern fly. Fl. 35 is the junction with kRttikA.
The solar zodiac defines the path of the sun into 12 parts or rAshi (রাশি) (quantity), almost as many as there are full moons in a year. The names of the constellation in Indian texts: meSa (মেষ) (sheep) or aja (অজ) (goat), vRSa (বৃষ)or RSava (ঋষব) (bull, possibly related to impregnation, ultimately as rain impregnates the earth), mithuna (মিথুন)(couple and united), karkaTa (কর্কট) (crab, probably from a word related to head), siMha (সিংহ) (lion, probably from a word meaning powerful), kanyA (কন্যা) (girl, daughter, or virgin, from a word meaning small), tulA (তুলা) (scale, from a word meaning to raise as in to weigh), vRshcika (বৃশ্চিক) (scorpion, maybe from a word for cleaver), dhanuH (ধনুঃ) (bow, from a word meaning to cause to run quickly), makara (মকর) (crocodile, originally a sea monster) or mRga (মৃগ) (game animal) or shiMshumAra (শিংশুমার) (gangetic dolphin), kumbha (কুম্ভ) (water jar), and mIna (মীন) (fish), show clear conistency in meaning, but not necessarily in etymology with the corresponding western zodiac of Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, and Pisces. Another choice of names, using the words, kRYA (কৃয়া), tAouri (তাওউরি), jituma or tituma (জিতুম, তিতুম), kulIra (কুলীর), leYa (লেয়), pArthenA (পার্থেনা), juga (জুগ) or agni (অগ্নি), kaurpya (কৌর্প্য), taukSika (তৌক্ষিক), akokera (অকোকের), hRdroga or udruvaga (হৃদ্রোগ, উদ্রুবগ), and ittha (ইত্থ), close in sound to the Greek names for these constellations (namely, krios or aigokeros, tauros, didumoi, karkinos or kolouros, leon, kori or parthenos, khilai or zugon, skorpios, toseutis, athalpis or aigekeros, hydrochoös, and ikhthue) have also been used. Sometimes, the constellations are also named by a prominent nakSatra within it.
This system probably started in the sumerian region and spread over. There is some evidence that initially these signs formed pairs which were then named: thus both Libra and Scorpio were considered as the single constellation Scorpio (and the list started with Taurus.
The most important figures other than prajApati described under hastA above was probably RkSa (ঋক্ষ) meaning bear (literally hurting) or sapta-RSi (সপ্তর্ষি) meaning the seven (often used for many) sages (literal meaning might have been seers). The association of bear with this is rare in Indian texts, except for the really old part of the Rgveda (ঋগ্বেদ), but is common in almost all other Indo european cultures: thus, in Latin, it was called the Ursa Major. Its seven stars have been called kratu (ক্রতু) (meaning design, determination, ability, judgement, ceremony; α), pulaha (পুলহ) (an old name which may be related to words for large or high or hair and jump or spring or bound; β), pulastya (পুলস্ত্য) (related to a word meaning wearing straight hair; γ), atri (অত্রি) (devourer; δ), aGgiraH (অঙ্গিরঃ) (related to word meaning marked, cognate word in greek gives us ἄγγελος and ἄγγαρος; ε), marIci (মরীচি) (particle of light; η), and brahmA or vaSiSTha (ব্রহ্মা, বশিষ্ঠ) (words related to growth and best or most wealthy respectively; ζ). Sometimes the names of the seven great vedic sages Gotama (গোতম) (best ox), Bharadvaja (ভরদ্বজ) (bearing speed), Visvamitra (বিশ্বামিত্র) (friend of all), Jamadagni (জমদগ্নি) (devouring fire), Vasistha বশিষ্ঠ (richest), Kasyapa (কশ্যপ) (drunkard, with black teeth), and Atri (অত্রি) (devourer) are used instead.
The entire nether world is the night sky with varuNa (বরুণ) holding the tree that is at plakSa prasravana (প্লক্ষ প্রস্রবন) (‘source of the fig tree’; it is where the river sarasvati (সরস্বতী), i.e. the one with lakes, arises) with its roots in this nether world: as night turns to day, the world flips over to face the day sky. In some mythology, it is the sun that flips instead after moving from west to east with its dark side facing us. In any case, at night the entire sky turns counterclockwise about the pole star with this tree as the axis and the Ursa Major is seen as a ladle (কোশ) that pours out every night.
Other important constellations were the lokapAlas (লোকপালঃ) (protector of the ‘visible’ or worlds), which might have been Sirius to the east, Ursa Major to the north, Corvus to the west, and Argo Navis to the South.
In addition to the nakSatra described above, ashvinI (অশ্বিনী) has also been used for the four stars of Equuleus (α, β, γ, and δ), and for Sagittarius. The name prajApati was also very common being used not only for the figure described under hastA above, it was used for the Orion and the Corvus. Similarly, siMsumAra referred not only to Capricorn, but also to Dolphin and to Draco.
Other individual stars which were named include agastya (অগস্ত্য) (traditionally derived as one who throws the unmoving, i.e. a mountain) which is α (Carinae or Canopus) of argo navis, brahma hRdaya (ব্রহ্মহৃদয়) (heart of brahma, the eternal principle, related to a word for growth) which is α-Aurigae (Capella), AryamaNa (আর্যমণ) (belonging to aryaman (অর্যমা) meaning a friend, word ultimately related to a word for straight) which is either α-Aurigae (Capella) or α-Boötes (arctaurus), tisRja (তিসৃজ) (born thrice?) which was either α-Boötes (arctaurus) or α-Canis Majoris (sirius), mRgavyAdha (মৃগব্যাধ) (piercer of the hunted, i.e. game animal) or lubdhaka (লুব্ধক) (bewilderer, hunter, see the prajapati myth for reasons) or saramA (সরমা) (female dog, mother of the hounds of death, from a word meaning quick) which was α-Canis Majoris (sirius), andhaka (অন্ধক) (blind) or invakA (ইন্বক) (pervading) which was λ-Orionis, agni (অগ্নি) (fire) or hutabhuj (হুতভুক্) (eater of oblation) which was β-Tauri (the same as γ-Aurigae), ambA or arundhatI (অম্বা, অরুন্ধতী) (mother and one that does not obstruct, respectively) which was η-Pleiades (Alcyone), grahadhara (গ্রহধার) (holder of the seizers, i.e. support of the planets) or dhruva (ধ্রুব) (fixed) which was α of Ursa Minor, and apami-atsa (অপম্যত্স?) (ap means water) which was θ (or δ?) Virginis.
As the greek texts became familiar to Indian, some of the names got transformed into Indian words. As an example, Andromeda became antamarda (অন্তমর্দ), Cassiopeia became kashyapi (কশ্যপি), and Cepheus became kapi (কপি).
The milky way galaxy itself was seen as the path of aryaman (অর্যম্ণঃ পন্থাঃ) or the ganges (the name etymologically related to going) of the sky (আকাশগঙ্গা).