- the sky in the shape of an inverted bowl along with millions of stars seem to revolve around you: this is nothing but the celestial sphere in astronomical terminology.
- the sun, moon and the visible planets always appear in a line, rather, an arc: this arc or line is the ecliptic; in astronomical lingo it's the projection of the earth's orbital plane on the celestial sphere; simplistically it signifies the plane on which earth orbits round the sun; it's also roughly the plane on which all the planets orbit round the sun.
- the line, on which appear the sun, moon and the planets, is marked by a number of bright fixed stars which can divide the line into several compartments - the sun, moon and the planets seem to be moving from one of these compartments to the other in a fixed cycle of time: the Babylonians were the first to study these stars, which are located close to the earth's orbital plane and which later constituted the twelve zodiac constellations; for the Rig Vedic Aryans these stars that compartmentalize the ecliptic constituted the twenty seven asterisms, nakshatras; the number twenty seven comes from the twenty seven lunar days that roughly make a lunar month - dividing the ecliptic into twenty seven compartments makes the moon appear everyday in a new compartment, which is eventually called lunar mansion.
- there's only one star that doesn't seem to revolve - it doesn't move, doesn't rise, doesn't set, remains at the same place as long as the night sky is visible: this is the Polestar, the star that's located exactly to the north of or above the earth's north pole; each and every star appears to be rotating around the Polestar.
sapta yuñjanti ratham ekacakram eko aśvo vahati saptanāmā |trinābhi cakram ajaram anarvaṃ yatremā viśvā bhuvanādhi tasthuḥ || 1.164.02
Seven to the one-wheeled chariot yoke the Courser; bearing seven names the single Courser draws it.Three-naved the wheel is, sound and undecaying, whereon are resting all these worlds of being. 1.164.02
imaṃ ratham adhi ye sapta tasthuḥ saptacakraṃ sapta vahanti aśvāḥ |sapta svasāro abhi saṃ navante yatra ghavāṃ nihitā sapta nāma || 1.164.03
The seven who on the seven-wheeled car are mounted have horses, seven in tale, who draw them onward.
Seven Sisters utter songs of praise together, in whom the names of the seven Cows are treasured. 1.162.03
acikitvāñ cikituṣaś cid atra kavīn pṛchāmi vidmane na vidvān |vi yas tastambha ṣaḷ imā rajāṃsi ajasya rūpe kimapi svid ekam || 1.164.06
I ask, unknowing, those who know, the sages, as one all ignorant for sake of knowledge,What was that ONE who in the Unborn's image hath stablished and fixed firm these worlds' six regions. 1.164.06
indraś ca yā cakrathuḥ soma tāni dhurā na yuktā rajaso vahanti || 1.164.19
And what so ye have made, Indra and Soma, steeds bear as ’twere yoked to the region's car-pole. 1.164.19
viśvakarmā vimanā ād vihāyā dhātā vidhātā paramota sandṛk |teṣām iṣṭāni sam iṣā madanti yatrā saptaṛṣīn para ekam āhuḥ || 10.82.02
Mighty in mind and power is Visvakarman, Maker, Disposer, and most lofty Presence.Their offerings joy in rich juice where they value One, only One, beyond the Seven Ṛṣis. 10.82.02
yo naḥ pitā janitā yo vidhātā dhāmāni veda bhuvanāni viśvā |yo devānāṃ nāmadhā eka eva taṃ sampraśnam bhuvanā yanti anyā || 10.82.03
Father who made us, he who, as Disposer, knoweth all races and all things existing,
ta āyajanta draviṇaṃ sam asmā ṛṣayaḥ pūrve jaritāro nabhūnā |asūrte sūrte rajasi niṣatte ye bhūtāni samakṛṇvan imāni || 10.82.04
To him in sacrifice they offered treasures,—Ṛṣis of old, in numerous troops, as singers,Who, in the distant, near, and lower region, made ready all these things that have existence. 10.82.04
paro divā para enā pṛthivyā paro devebhir asurair yad asti |kaṃ svid garbhaṃ prathamaṃ dadhra āpo yatra devāḥ samapaśyanta viśve || 10.82.05
That which is earlier than this earth and heaven, before the Asuras and Gods had being,—What was the germ primeval which the waters received where all the Gods were seen together? 10.82.05
tam id garbhaṃ prathamaṃ dadhra āpo yatra devāḥ samaghachanta viśve |ajasya nābhāv adhi ekamarpitaṃ yasmin viśvāni bhuvanāni tasthuḥ || 10.82.06
Here it's worth mentioning that the Seven Sages of Saptarshi, the Big Dipper asterism, made a perfect circle around the Polestar Thuban during the timeline of Rig Veda (~ 1700 BC). But now the stars of Big Dipper don't make a tight circle around the current Polestar Polaris. The term 'beyond the seven sages' surely made much more sense when the Polestar was really at the center.The waters, they received that germ primeval wherein the Gods were gathered all together.It rested set upon the Unborn's navel, that One wherein abide all things existing. 10.82.06
Finally let's see how the ideas about these constellations impacted the calendar system in India. It's worth mentioning that a very precise and scientific calendar system has been in place in India since the Rig Vedic times.
Let's recall the following diagram we've seen in the discussions on Surya's Bridal. It depicts the scenario during 3000 BC - sun is in Mrigashira on Vernal Equinox and Uttara Phalguni on Summer Solstice. From a few verses of RV it can be deduced that one of the beginnings of year during Rig Vedic times is this Summer Solstice when the sun is in Uttara Phalguni. On the other hand another name of Mrigashira is Agrahayana, which means the commencement of a year. This means that the Vernal Equinox is also a beginning of year. In fact one or more of the four cardinal points - the two equinoxes and two solstices - have been considered beginnings of year in RV.
If Spring Equinox is taken as the beginning of the year then the year starts precisely when the sun enters into the zodiac Mesha, Aries. Though Vernal Equinox is no longer at the beginning of Mesha, still, even now, half of India (north, east, Tamil Nadu) celebrates new year when sun enters into Mesha, sometime around 14th April - it's called Vaishakhi. The rest of India (Maharashtra, Gujarat, south), celebrates new year on the new moon day just after the Vernal Equinox, sometime in late March or early April - it's called Ugadi. Beginning of a month on a new moon day has been the tradition in India since long. In fact that's the most logical thing to do for a lunar or a luni-solar calendar. In a luni-solar calendar the twelve lunar months totaling to roughly 356 days are synced up with solar year of roughly 365 days by adding an extra or intercalary thirteenth month from time to time. Rig Veda has reference to intercalary month.