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Kalamana (Samskrit: कालमानम्) broadly refers to the measurement of time (Kala). Bharatiya shastrajnas have explained the various macrocosmic and microcosmic time systems and depending on the needs of particular topics in astronomy, different scales and units of time are used. On the macrocosmic scale, the Yuga system has been described, whereas on the microcosmic scale, a small unit of time Truti (1/33750 of a second) has been mentioned by Bhaskara II. We mention the macrocosmic time scales (Svetavaraha kalpa, Vaivasvata Manvantara etc) only in the samkalpa of our daily puja rituals.

Kalamana (Samskrit: कालमानम्) broadly refers to the measurement of time ([[Kala (कालः)|Kala]]). Bharatiya shastrajnas have explained the various macrocosmic and microcosmic time systems and depending on the needs of particular topics in astronomy, different scales and units of time are used. On the macrocosmic scale, the Yuga system has been described, whereas on the microcosmic scale, a small unit of time Truti (1/33750 of a second) has been mentioned by Bhaskara II. We mention the macrocosmic time scales (Svetavaraha kalpa, Vaivasvata Manvantara etc) only in the samkalpa of our daily puja rituals.<ref name=":2" />

== Introduction ==

== Introduction ==

Many of these factors are based on simple natural observations, earth, moon and planetary motions and seasons - all of which are pratyaksha pramanas (visible evidence) in the nature around us manifesting the environmental changes. It is common knowledge that it is a day with sunrise, a night with sunset, high and low tides with lunar movements, rashis associated with the movement of moon in nakshatras, formation of new leaves and leaf shedding indicates seasonal change with Vishvat (equinoxes) so on and so forth.  

Many of these factors are based on simple natural observations, earth, moon and planetary motions and seasons - all of which are pratyaksha pramanas (visible evidence) in the nature around us manifesting the environmental changes. It is common knowledge that it is a day with sunrise, a night with sunset, high and low tides with lunar movements, rashis associated with the movement of moon in nakshatras, formation of new leaves and leaf shedding indicates seasonal change with Vishvat (equinoxes) so on and so forth.  

It is only with deep respect for the intellect and keen observation of our ancient maharshis, rsis and later day ganita and jyotisha shastrajnas that we can appreciate the systematic work done by them - not requiring huge telescopes or light measuring instruments - to leave a legacy of astronomical wealth for us.

It is only with deep respect for the intellect and keen observation of our ancient maharshis, rsis and later day [[Ganita Shastra (गणितशास्त्रम्)|ganita]] and jyotisha shastrajnas that we can appreciate the systematic work done by them - not requiring huge telescopes or light measuring instruments - to leave a legacy of astronomical wealth for us.

Here we discuss a few important astronomical concepts, briefly, that are in use in our present day calendars, without delving deep into the mathematical calculations used to arrive at them.  

Here we discuss a few important astronomical concepts, briefly, that are in use in our present day calendars, without delving deep into the mathematical calculations used to arrive at them.  

== नवमानानि ॥ Nine Kinds of Time ==

== नवमानानि ॥ Nine Kinds of Time ==

Surya Siddhanta is one of the oldest and accepted by many scholars as an authentic source of information regarding the astronomical calculations and specifications. Manadhyaya (14th Adhyaya) of Surya Siddhanta is referred here.<blockquote>ब्राह्मम् दिव्यम् तथा पित्र्यम् प्राजापत्यम् गुरोस् तथा । सौरम् च सावनम् चान्द्रम् आर्क्षम् मानानि वै नव ॥</blockquote><blockquote>चतुर्भिर्व्यवहारोऽत्र सौरचान्द्रार्क्षसावनैः।बार्हस्पत्येन षष्ट्यब्दा ज्ञेया नान्यैस्तु नित्यशः॥ (Sury. Sidd. 14.1-2)<ref name=":0">Surya Siddhanta ([https://sa.wikisource.org/wiki/%E0%A4%B8%E0%A5%82%E0%A4%B0%E0%A5%8D%E0%A4%AF%E0%A4%B8%E0%A4%BF%E0%A4%A6%E0%A5%8D%E0%A4%A7%E0%A4%BE%E0%A4%A8%E0%A5%8D%E0%A4%A4_%E0%A4%AE%E0%A4%BE%E0%A4%A8%E0%A4%BE%E0%A4%A7%E0%A5%8D%E0%A4%AF%E0%A4%BE%E0%A4%AF%E0%A4%83 Adhyaya 14])</ref></blockquote>There are nine Manas or measurements of time (kinds of time). They are

Surya Siddhanta is one of the oldest texts and accepted by many scholars as an authentic source of information regarding the astronomical calculations and specifications. Manaadhyaya (14th Adhyaya) of Surya Siddhanta is referred here to understand the different kinds of Kala that we use in day to day lives.<blockquote>ब्राह्मम् दिव्यम् तथा पित्र्यम् प्राजापत्यम् गुरोस् तथा । सौरम् च सावनम् चान्द्रम् आर्क्षम् मानानि वै नव ॥</blockquote><blockquote>चतुर्भिर्व्यवहारोऽत्र सौरचान्द्रार्क्षसावनैः।बार्हस्पत्येन षष्ट्यब्दा ज्ञेया नान्यैस्तु नित्यशः॥ (Sury. Sidd. 14.1-2)<ref name=":0">Surya Siddhanta ([https://sa.wikisource.org/wiki/%E0%A4%B8%E0%A5%82%E0%A4%B0%E0%A5%8D%E0%A4%AF%E0%A4%B8%E0%A4%BF%E0%A4%A6%E0%A5%8D%E0%A4%A7%E0%A4%BE%E0%A4%A8%E0%A5%8D%E0%A4%A4_%E0%A4%AE%E0%A4%BE%E0%A4%A8%E0%A4%BE%E0%A4%A7%E0%A5%8D%E0%A4%AF%E0%A4%BE%E0%A4%AF%E0%A4%83 Adhyaya 14])</ref></blockquote>There are nine Manas or measurements of time (kinds of time). They are

# ब्राह्मम् ॥ Braahmam (Of Brahma)

# ब्राह्मम् ॥ Braahmam (Of Brahma)

# दिव्यम् ॥ Divyam (Of Devatas)

# दिव्यम् ॥ Divyam (Of Devatas)

# चान्द्रम् ॥ Of Chandra

# चान्द्रम् ॥ Of Chandra

# आर्क्षम् (नाक्षत्रम्) ॥ Aarksham (Of Nakshatra)

# आर्क्षम् (नाक्षत्रम्) ॥ Aarksham (Of Nakshatra)

The Manas which are used in daily activities are four in number - सौरचान्द्रार्क्षसावनैः । Solar, Lunar, Sidereal, and the Savana (Civil). The Mana of Jupiter (Barhaspatya) is used for determining the Shasthtyabda (60 Samvatsaras) or attaining 60 years of age while the remaining four are not used on a daily basis.<ref name=":1">Pt Mahavir Prasad Srivastav (1940 First Edition) ''Surya Siddhanta with Vijnana Bhashya, Parts 1 and 2.'' Allahabad: Dr. Ratnakumari Svadhyaya Sansthan. (Page 794 -)</ref>

The Manas, measures of time, which are used in daily activities are four in number - सौरचान्द्रार्क्षसावनैः । Solar, Lunar, Sidereal, and the Savana (Civil). The Mana of Jupiter (Barhaspatya) is used for determining the Shasthtyabda (60 Samvatsaras) or calculation of how a person attains 60 years of age. The remaining four Manas are not used for daily activities.<ref name=":1">Pt Mahavir Prasad Srivastav (1940 First Edition) ''Surya Siddhanta with Vijnana Bhashya, Parts 1 and 2.'' Allahabad: Dr. Ratnakumari Svadhyaya Sansthan. (Page 794 -)</ref>

 

 

== सौरमानम् ॥ Saura Mana ==

== सौरमानम् ॥ Saura Mana ==

It is long known to our ancient seers that it is the earth that revolves around the sun in an ecliptic path. However, the time is calculated based on using the earth as a reference, and thus we say sun is revolving around the earth. We see in the sky that due to diurnal motion, the Sun rises in the eastern horizon, moves up in the sky westward and sets in the western horizon. From the sunset to the next sunrise, it will be below the horizon during the night. It is common knowledge all over the world that this period of time between the sunrise and sunset is called a Day. However, our seers have calculated and defined a Day, not just with respect to the Earth but also with other cosmic references and specified where such a measure of time is to be used.

It is long known to our ancient seers that it is the earth that revolves around the sun in an ecliptic path. However, the time is calculated based on using the earth as a reference, and thus we say sun is revolving around the earth. We see in the sky that due to the diurnal motion, the Sun rises in the eastern horizon, moves up in the sky westward and sets in the western horizon. From the sunset to the next sunrise, it will be below the horizon during the night. It is common knowledge all over the world that this period of time between the sunrise and sunset is called a Day. However, our seers have calculated and defined a Day, not just with respect to the Earth but also with other cosmic references and specified the purpose where such a measure of time is to be used.

==== सौरदिनम् ॥ Saura Dina (Solar Day) ====

=== सौरदिनम् ॥ Saura Dina (Solar Day) ===

<blockquote>सौरेण द्युनिशोर्मानं षडशीतिमुखानि च। अयनं विषुवच्चैव सम्क्रान्तेः पुण्यकालता॥ (Sury. Siddh. 14.3)<ref name=":0" /></blockquote>With reference to Earth the Sun's motion along the ecliptic path, in the rashi, is about 1° per day. This is called a Solar Day.  

<blockquote>सौरेण द्युनिशोर्मानं षडशीतिमुखानि च। अयनं विषुवच्चैव सम्क्रान्तेः पुण्यकालता॥ (Sury. Siddh. 14.3)<ref name=":0" /></blockquote>With reference to Earth the Sun's motion along the ecliptic path, in the rashi, is about 1° per day. This is called a Solar Day.  

There are four Shadasheeti Mukhas in a year. <blockquote>तुलादि षडशीत्यह्नाम् षडशीतिमुखम् क्रमात् । तच्चतुष्टयम् एव स्याद् द्विस्वभावेषु राशिषु ॥ (Sury. Siddh. 14.4)</blockquote>Every eighty-sixth solar day reckoned from the time of Tula Sankramana (Day the Sun enters Tula rashi) is called Shadasheeti Mukha in succession. They are four in number and happen when Sun is in 4 Dvisvabhava Rashis, namely Dhanas (26°of Saggitarius), Meena (22° of Pisces), Mithuna (18° of Gemini) and Kanya (14° of Virgo) rashis.  

There are four Shadasheeti Mukhas in a year. <blockquote>तुलादि षडशीत्यह्नाम् षडशीतिमुखम् क्रमात् । तच्चतुष्टयम् एव स्याद् द्विस्वभावेषु राशिषु ॥ (Sury. Siddh. 14.4)</blockquote>Every eighty-sixth solar day reckoned from the time of Tula Sankramana (Day the Sun enters Tula rashi) is called Shadasheeti Mukha in succession. They are four in number and happen when Sun is in 4 Dvisvabhava Rashis, namely Dhanas (26°of Saggitarius), Meena (22° of Pisces), Mithuna (18° of Gemini) and Kanya (14° of Virgo) rashis.  

==== Pitrpaksha ====

==== पितृपक्षम् ॥ Pitrpaksha ====

<blockquote>ततः शेषाणि कन्याया यान्य् अहानि तु षोडश । क्रतुभिस् तानि तुल्यानि पितृऋणाम् दत्तम् अक्षयम् ॥ (Sury. Siddh. 14.6)</blockquote>After the 4th Shadasheethi Mukha (in Kanya), the remaining 16 solar days of the solar month when Sun is in Kanya rashi are equivalent to the time of Yajna, (kala when any good actions give great merit) and in these days dana offered to Pitrs will give infinite merit.<ref>Pt. Bapu Deva Sastri (1861) ''Translation of the Surya Siddhanta and Revision of Siddhanta Siromani Translated by Lancelot Wilkinson.'' Calcutta: Asiatic Society. (Pages 91-)</ref>

<blockquote>ततः शेषाणि कन्याया यान्य् अहानि तु षोडश । क्रतुभिस् तानि तुल्यानि पितृऋणाम् दत्तम् अक्षयम् ॥ (Sury. Siddh. 14.6)</blockquote>After the 4th Shadasheethi Mukha (in Kanya), the remaining 16 solar days of the solar month when Sun is in Kanya rashi are equivalent to the time of Yajna, (kala when any good actions give great merit) and in these days dana offered to Pitrs will give infinite merit.<ref>Pt. Bapu Deva Sastri (1861) ''Translation of the Surya Siddhanta and Revision of Siddhanta Siromani Translated by Lancelot Wilkinson.'' Calcutta: Asiatic Society. (Pages 91-)</ref>

From this we understand that, Shraddha for Pitrs should happen when Sun is in Kanya rashi starting from 15° to 30° according to Saura Mana. However, in the present times, Saura Mana is not used. According to Purnimanta system, Krishna paksha of Ashvini month (dark half of month of Ashvini) and according to Amanata system, Krishna paksha of Bhadrapada month (dark half of the month of Bhadrapada) i.e., calculated according to Chandra Mana are the days of Pitrpaksha followed by people.<ref name=":1" />  

From this we understand that, Shraddha for Pitrs should happen when Sun is in Kanya rashi starting from 15° to 30° according to Saura Mana. However, in the present times, Saura Mana is not used. According to Purnimanta system, Krishna paksha of Ashvini month (dark half of month of Ashvini) and according to Amanta system, Krishna paksha of Bhadrapada month (dark half of the month of Bhadrapada) i.e., calculated according to Chandra Mana are the days of Pitrpaksha followed by people.<ref name=":1" />

==== Vishuvats ====

==== सङ्क्रान्तयः ॥ Sankrantis ====

<blockquote>भचक्रनाभौ विषुवद्द्वितीयं समसूत्रगम् । अयनद्वितयं चैव चतस्रः प्रथितास्तु ताः॥ (Sury. Siddh. 14.7)</blockquote>

'''1 Saura Dina (Solar Day) = Movement of Sun in a Rashi by 1 degree in ecliptic path'''

The time at which Sun enters into an new rashi is termed Sankranti. <blockquote>भचक्रनाभौ विषुवद्द्वितीयं समसूत्रगम् । अयनद्वितयं चैव चतस्रः प्रथितास्तु ताः॥ (Sury. Siddh. 14.7)</blockquote>In the middle of the nakshatra chakra (sphere of stars) the two equinoxes (Vishuvats in Mesha and Tula rashis) are diametrically opposed and so are the two solistices (Ayanas in Karkataka and Makara) in the ecliptic path.

==== Purpose of Saura Dina ====

 

==== उत्तरायणम् दक्षिणायनम् च॥ Uttarayana and Dakshinayana ====

 

=== Purpose of Saura Dina ===

# Determining the length of the day and night

# Determining the length of the day and night

# Shadashiiti Mukhas

# Shadashiiti Mukhas

# Determine Uttarayana and Dakshinayana (the northern and southern paths of the Sun)

# Determine Uttarayana and Dakshinayana (the northern and southern paths of the Sun)

# Equinoxes and Vishuvats  

# Equinoxes and Solistices (Vishuvats etc)

# Sankrantis (the time of entry of Sun into a new rashi)

# Sankrantis (the time of entry of Sun into a new rashi)

=== सौरमासं सौरवर्षं च ॥ Solar Day and Year ===

=== सौरमासं सौरवर्षं च ॥ Solar Month and Year ===

The time taken by the Sun to complete a revolution (360°) around the Earth, as observed from the Earth, is defined as a Saura Varsha (Solar Year)

 

 

The time taken by the Sun to complete a revolution (360°) around the Earth, as observed from the Earth, is defined as a Saura Varsha (Solar Year). To complete the 360° revolution the Sun takes about 365.25 Savana or Civil days.<ref name=":2" />

 

 

 

 

 

== सावनमानम् ॥ Savana Mana ==

== सावनमानम् ॥ Savana Mana ==

=== सावनदिनम्॥ Savana Dina (Civil Day) ===

=== सावनदिनम्॥ Savana Dina (Civil Day) ===

<blockquote>उदयाद् उदयम् भानोः सावनम् तत् प्रकीर्त्यते । सावनानि स्युरेतानि यज्ञकालविधिस्तु तैः ॥ </blockquote><blockquote>सूतकादिपरिच्छेदो दिनमासाब्दपास्तथा । मध्यमा ग्रहभुक्तिस्च सावनेन प्रकीर्त्यते ॥ (Sury. Siddh. 14.18)<ref name=":0" /></blockquote>The duration between two successive risings of the Sun is called a Savana Dina or Civil Day.<ref name=":1" />

<blockquote>उदयाद् उदयम् भानोः सावनम् तत् प्रकीर्त्यते । सावनानि स्युरेतानि यज्ञकालविधिस्तु तैः ॥ </blockquote><blockquote>सूतकादिपरिच्छेदो दिनमासाब्दपास्तथा । मध्यमा ग्रहभुक्तिस्च सावनेन प्रकीर्त्यते ॥ (Sury. Siddh. 14.18-19)<ref name=":0" /></blockquote>The duration between two successive risings of the Sun is called a Savana Dina or Civil Day.<ref name=":1" />

Observations of sunrise over a very long time has revealed that the duration of a day is not constant but varies from day to day although very slightly. An average calculated based on the observations is referred to as the Mean Solar Day or Mean Civil day. Savana Dina is divided into 60 equal parts called Ghatikas or 24 equal parts called Hora (hours). Thus the 24 hour day that is used for our regular daily activities is the Savana Dina.<ref name=":2">Rao, S. Balachandra. (2000) ''Indian Astronomy, An Introduction.'' Hyderabad: Universities Press (India) Limited. (Page 39-50)</ref>

Observations of sunrise over a very long time has revealed that the duration of a day is not constant but varies from day to day although very slightly. An average calculated based on the observations is referred to as the Mean Solar Day or Mean Civil day. Savana Dina is divided into 60 equal parts called Ghatikas or 24 equal parts called Hora (hours). Thus the 24 hour day that is used for our regular daily activities is the Savana Dina.<ref name=":2">Rao, S. Balachandra. (2000) ''Indian Astronomy, An Introduction.'' Hyderabad: Universities Press (India) Limited. (Page 39-50)</ref>

  '''1 Savana Day (Civil Day) = 24 Hours'''

  '''1 Savana Day (Civil Day) = 60 Ghatikas = 24 Hours'''

==== Purpose of Savana Dina ====

==== Purpose of Savana Dina ====

=== तिथिः ॥ Tithi (Lunar Day) ===

=== तिथिः ॥ Tithi (Lunar Day) ===

<blockquote>अर्काद्विनिस्सृतः प्राचीं यद्यात्यहरहश्शशी। तच्चान्द्रमानम् अम्शैस्तु ज्ञेया द्वादशभिस्तिथिः॥ </blockquote><blockquote>तिथिः करणम् उद्वाहः क्षौरम् सर्वक्रियास् तथा। व्रतोपवासयात्राणाम् क्रिया चान्द्रेण गृह्यते॥ (Sury. Siddh. 14.12-13)<ref name=":0" /></blockquote>The time in which the Moon being separate from the Sun (after a conjunction) moves daily to the east is the measurement for the moon (चान्द्रमानम्) Chandra Mana. The time taken by the Moon to cover exactly an amount of 12° relative to the Sun, is defined as Tithi or Lunar Day.<ref name=":1" />

<blockquote>अर्काद्विनिस्सृतः प्राचीं यद्यात्यहरहश्शशी। तच्चान्द्रमानम् अम्शैस्तु ज्ञेया द्वादशभिस्तिथिः॥ </blockquote><blockquote>तिथिः करणम् उद्वाहः क्षौरम् सर्वक्रियास् तथा। व्रतोपवासयात्राणाम् क्रिया चान्द्रेण गृह्यते॥ (Sury. Siddh. 14.12-13)<ref name=":0" /></blockquote>The time in which the Moon being separate from the Sun (after a conjunction) moves daily to the east is the measurement for the moon (चान्द्रमानम्) Chandra Mana. The time taken by the Moon to cover exactly a distance of 12° relative to the Sun, is defined as Tithi or Lunar Day.<ref name=":1" />

 

 

 

If the Sun and Moon are moving in the same direction, in which case their celestial longitude is the same, as seen from the Earth, the moon is said to be "new" or it is called Amavasya or New Moon Day. After 24 hours the moon would have moved ahead of the Sun by about 12°10'. This increasing separation of the moon from the sun goes on at the rate of 12°10' per day until it reaches 360°. At this point the moon will be in conjunction (or in the same direction) as the sun, resulting in a new moon. The interval between two successive new moons is called the synodic period of the Moon ("synodic" means successive conjunctions of the same bodies). This synodic period of the Moon is defined as a Lunar month (Chandra Masa). Thus one lunar month = 29.530589 days (29 Days, 12 Hours, 44 Minutes, and 2.9 secs).<ref name=":2" />

Since the moon moves faster than the sun, starting from a new moon, the moon gains about 12° per day over the Sun, i.e., one Tithi per day, thus the chandra masa has 30 tithis. The half-lunar month from a new moon to the succeeding full moon is called Shukla Paksha (the bright fortnight) and the other half-lunar month from the full moon to next new moon is called Krshna Paksha (dark fortnight). The lunar month is a natural unit for a month. It is important to note that the beginning and end of a lunar month are naturally marked by two successive new moons.<ref name=":2" />

Dharmasindhu elaborates about the course of a lunar month, when the Moon goes through a cycle of phases, from new moon to full moon and then to new moon again. <blockquote>शुक्लप्रतिपदादिदर्शांन्तैश्चैत्रादिसंज्ञैर्द्वादशभिर्मासैश्चतुःपञ्चाशदधिकशतत्रयदिनैः सति मलमासे त्रयोदशभिर्मासैश्चान्द्रो वत्सरः॥ (Dhar. Sind. 1)<ref name=":3" /></blockquote>From the Shukla Pratipat tithi till the end of Amavasya, there are 30 tithis; together they constitute one Chandra-masa or Lunar month namely Chaitra, etc. 12 such Lunar months make up a Lunar Year having 354 days (savana days). When an Adhika masa is present there are 13 months a lunar year.

==== Purpose of Chandra Mana ====

=== Purpose of Chandra Mana ===

# Determination of Tithi, Karana (half of Tithi)

# Determination of Tithi, Karana (half of Tithi)

# Determine the time for samskaras like marriage

# Determine the auspicious time for samskaras like marriage

# Determine the appropriate time for activities such as shaving, tonsure

# Determine the appropriate time for activities such as shaving, tonsure

# To determine the time for Vratas, Upavasas, Yatras

# To determine the time for Vratas, Upavasas, Yatras

== नाक्षत्रमानम् ॥ Nakshatra Mana ==

== नाक्षत्रमानम् ॥ Nakshatra Mana ==

=== नाक्षत्रदिनम् ॥ Nakshatra Dina (Sidereal Day) ===

=== नाक्षत्रदिनम् ॥ Nakshatra Dina (Sidereal Day) ===

<blockquote>भचक्रभ्रमणम् नित्यम् नाक्षत्रम् दिनम् उच्यते। नक्षत्रनाम्ना मासास् तु ज्ञेयाः पर्वान्तयोगतः ॥ (Sury. Siddh. 14.15)<ref name=":0" /></blockquote>The time taken for one revolution of the sphere of stars is called a sidereal day.  

<blockquote>नाडी षष्ट्या तु नाक्षत्रमहोरात्रं प्रकीर्तितम् । तत्त्रिम्शता भवेन्मासः सावनोऽर्कोदयैःस्मृतः॥ (Sury. Siddh. 1.12)</blockquote>The time which contains sixty ghatikas is called a Nakshatra Ahoratra (a sidereal day and night) or Day and a Nakshatra masa (a sidereal month) consists of thirty Nakshatra Ahoratras. <blockquote>भचक्रभ्रमणम् नित्यम् नाक्षत्रम् दिनम् उच्यते। नक्षत्रनाम्ना मासास् तु ज्ञेयाः पर्वान्तयोगतः ॥ (Sury. Siddh. 14.15)<ref name=":0" /></blockquote>The time taken for one revolution of the sphere of stars is called a sidereal day. The time taken by the fixed stars to go around the earth is called a Nakshatra Dina or Sidereal Day; and this time is equal to the period of the rotation of the Earth.

The time taken by the fixed stars to go around the earth is called a Nakshatra Dina or Sidereal Day; and this time is equal to the period of the rotation of the Earth. Sidereal is a term used to refer to stars. It is important to note that the time taken by the fixed stars to go round the Earth once is not the same as that  taken by the Sun. While all the celestial bodies appear to move from the east to west due to the diurnal motion, the Sun would have moved from west to east along the ecliptic by about 1°, relative to the stars. Therefore, the fixed stars take a little less than 24 hours (mean civil day) to complete a rotation around the Earth. As a natural consequence if a particular star rises in the eastern horizon at a particular time today, it will rise about two hours earlier after 30 days, 4 hours earlier after 60 days, and so on.

Sidereal is a term used to refer to stars. It is important to note that the time taken by the fixed stars to go round the Earth once is not the same as that  taken by the Sun. While all the celestial bodies appear to move from the east to west due to the diurnal motion, the Sun would have moved from west to east along the ecliptic by about 1°, relative to the stars. Therefore, the fixed stars take a little less than 24 hours (mean civil day) to complete a rotation around the Earth. As a natural consequence if a particular star rises in the eastern horizon at a particular time today, it will rise about two hours earlier after 30 days, 4 hours earlier after 60 days, and so on.  

It is found that the fixed stars take about 3 minutes 56 seconds less than the Sun to go round the Earth once.  

It is found that the fixed stars take about 3 minutes 56 seconds less than the Sun to go round the Earth once.  

  '''1 Nakshatra Dina = 1 Savana Dina - 3 mins 56 secs = 23 Hrs 56 Mins 4 Secs'''

  '''1 Nakshatra Dina = 60 Ghatikas'''

 

'''1 Nakshatra Day = 1 Savana Dina - 3 mins 56 secs = 23 Hrs 56 Mins 4 Secs'''

==== Purpose of Nakshatra Dina ====

==== Purpose of Nakshatra Dina ====

  1 Saura Dina (Solar Day) = Movement of Sun in the Rashi by 1 degree

  1 Saura Dina (Solar Day) = Movement of Sun in the Rashi by 1 degree

  1 Tithi (Lunar Day) =  

  1 Tithi (Lunar Day) = Movement of Moon by 12 degrees

  1 Savana Dina (Civil Day) = 24 hours

  1 Savana Dina (Civil Day) = 24 hours