The ancient texts of Dharma describe the importance of Shastra.

अनेकसंशयोच्छेदि, परोक्षार्थस्य दर्शकम् ।

सर्वस्य लोचनं शास्त्रं, यस्य नास्तित्यन्ध एव सः ॥ [हितोपदेश]

The eliminator of doubts, the preacher of hidden secrets is Shastra, thus spoke the seers. Shastras are the true eyes of everyone, the one who lacks them is blind in the empire of intellectuals.

Shastras are said to be six, named as

• Shabda
• Jyautisha
• Nirukta
• Kalpa
• Shiksha
• Chhanda

शब्दशास्त्रं मुखं ज्यौतिषं चक्षुषी श्रोत्रमुक्तं निरुक्तञ्च कल्पः करौ ॥

या तु शिक्षा‌‌‍‌‍‌‍ऽस्य वेदस्य सा नासिका पादपद्मद्वयं छन्द आद्यैर्बुधैः ॥

[सिद्धांत शिरोमणि]

The Audible form of Ishwara is Veda. They have spiritual organs in form of Shastra. Shabda is mouth, Jyautisha is eye, Nirukta is ear, Kalpa is hand, Shiksha is nose and Chhanda are feet. So, why should we consider Jyautisha as part of Veda ? or as a VEDANGA ? Well, the great Bhaskaracharya [II] explains,

वेदास्तावद्यज्ञकर्मप्रवृत्ता यज्ञाः प्रोक्तास्ते तु कालाश्रयेण ।

शास्त्रादस्मात् कालबोधो यतः स्याद्वेदाङ्गत्वं ज्योतिषस्योत्तमस्मात् |

[सिद्धांत शिरोमणि]

As, the knowledge of time, planetary movements and their effects are the cause of Yajna, and other Vedic rituals, so the Shastra, named as Jyautisha is itself a part of Veda.

Why Jyautisha is so popular and widely recognized ?

अप्रत्यक्षाणि शास्राणि विवादस्तेषु केवलम् ।

प्रत्यक्षं ज्यौतिषं शास्त्रं चन्द्रार्कौ यत्र साक्षिणौ ॥

[ज्योतिर्निबंध]

The rest of Shastras are loosely based on theoretical platforms resulting into intellectual debates and conflicts, while Jyautisha enjoys the witness of the Sun and Moon making it evident and observable.

– ज्यौतिषाचार्य पं० ब्रजेश पाठक