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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 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>

== दिननिर्नयम् ॥ Dina Nirnaya ==

== 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 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.

=== 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.  

==== षडशीतिमुखानि ॥ Shadasheeti Mukhas ====

==== षडशीतिमुखानि ॥ Shadasheeti Mukhas ====

तुलादि षडशीत्यह्नाम् षडशीतिमुखम् क्रमात् । तच्चतुष्टयम् एव स्याद् द्विस्वभावेषु राशिषु ॥

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.

षड्विम्शे धनुषो भागे द्वाविम्शे निमिषस्य च । मिथुनाष्टादशे भागे कन्यायास् तु चतुर्दश॥

<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>

 

==== Vishuvats ====

==== Vishuvats ====

ततः शेषाणि कन्याया यान्य् अहानि तु षोडश । क्रतुभिस् तानि तुल्यानि पितृऋणाम् दत्तम् अक्षयम् ॥

<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'''

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

# Equinoxes and Vishuvats  

# Equinoxes and Vishuvats  

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

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

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

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

# Determine the rulers of the day, month and year

# Determine the rulers of the day, month and year

# To calculate the mean motion of planets.

# To calculate the mean motion of planets.

=== तिथिः ॥ Tithi (Lunar Day) ===

=== तिथिः ॥ Tithi (Lunar Day) ===

# 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

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

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

  1 Nakshatra Dina (Sidereal Day) = 23 Hrs 56 Mins 4 Secs

  1 Nakshatra Dina (Sidereal Day) = 23 Hrs 56 Mins 4 Secs

== Four Other Manas ==

== Four Other Manas ==

=== पितृमानम् ॥ Pitr Mana ===

=== पितृमानम् ॥ Pitr Mana ===

<blockquote>त्रिम्शता तिथिभिर्मासश्चान्द्रः पित्र्यमहः स्मृतम्। निशा च मासपक्षान्ते तयोर्मध्ये विभागतः॥ (Sury. Siddh. 14.14)<ref name=":0" /></blockquote>Thirty tithis make a lunar month (mentioned under Tithis) which constitutes one day and night for the Pitrs. The end of Chandramasa (lunar month) i.e., the end of the New moon day (Amavasya) corresponds to the noon time for the Pitrs and the end of the Full moon day (Purnima) corresponds to the midnight time for the Pitrs. Thus the middle of Shukla Ashtami tithi corresponds to the start of the day for Pitrs and the middle of Krshna Ashtami tithi corresponds to the start of the night for the Pitrs.<ref name=":2" /> The Bhugola Adhyaya of Surya Siddhanta further discusses this topic establishing Amavasya as the noon time and Purnima as midnight for Pitrloka (Page 767-768 of Reference<ref name=":1" />).

<blockquote>त्रिम्शता तिथिभिर्मासश्चान्द्रः पित्र्यमहः स्मृतम्। निशा च मासपक्षान्ते तयोर्मध्ये विभागतः॥ (Sury. Siddh. 14.14)<ref name=":0" /></blockquote>Thirty tithis make a lunar month (mentioned under Tithis) which constitutes one day and night for the Pitrs. The end of Chandramasa (lunar month) i.e., the end of the New moon day (Amavasya) corresponds to the noon time for the Pitrs and the end of the Full moon day (Purnima) corresponds to the midnight time for the Pitrs. Thus the middle of Shukla Ashtami tithi corresponds to the start of the day for Pitrs and the middle of Krshna Ashtami tithi corresponds to the start of the night for the Pitrs.<ref name=":2" /> The Bhugola Adhyaya of Surya Siddhanta further discusses this topic establishing Amavasya as the noon time and Purnima as midnight for Pitrloka (Page 767-768 of Reference<ref name=":1" />).