Which are the Five faces of Lord Shiva?
Taittariya Aranyaka of YajurVeda from 10.17.1 to 10.21.1 contains five mantras and first word of each mantra represents each face of Lord SadaShiva. These Mantras are also in AtharvaVeda Parishista.
सद्योजातं प्रपद्यामि सद्योजाताय.....वामदेवाय नमो ज्येष्ठाय नमः ....अघोरेभ्योऽथ घोरेभ्यो घोरघोरतरेभ्यः ।.......तत्पुरुषाय विद्महे महादेवाय धीमहि ।.... ईशानः सर्वविद्यानामीश्वरः सर्वभूतानां
sadyojātaṃ prapadyāmi sadyojātāya ..... vāmadevāya namo jyeṣṭhāya namaḥ ....aghorebhyo'tha ghorebhyo ghoraghoratarebhyaḥ ।.......tatpuruṣāya vidmahe mahādevāya dhīmahi ।.... īśānaḥ sarvavidyānāmīśvaraḥ sarvabhūtānāṃ
Sayana Commentary on Taittariya Aranyaka also says these represents five faces of Lord SadaShiva. Srimad Bhagvatam in this chapter also states these five mantras represent Five faces of Lord SadaShiva:
मुखानि पञ्चोपनिषदस्यवेश यैस्त्रिंशदष्टोत्तरमन्त्रवर्ग ।
यतच्छिवाख्यं परमात्मतत्त्वं देव स्वयंज्योतिरवास्थितिस्ते।।
O lord, the five important Vedic mantras are represented by your five faces, from which the thirty-eight most celebrated Vedic mantras have been generated. Your Lordship, being celebrated as Lord Śhiva, is self-illuminated. You are directly situated as the supreme truth, known as Paramātmā.
Hence the five faces of Lord SadaShiva are:
Regarding position of faces and which face represents which direction it's mentioned in several Puranas like Shiva Purana, Linga Purana etc...
Manava Shrauta Sutra also gives description of direction of faces of SadaShiva also discussed in this question. Manava Shrauta Sutra in the section Rudra Japa Vidhãnam state:
सद्यो जात इत्यस्य सद्योजात ऋषिर्ब्रह्मा देवता त्रिष्टुपछन्दः हंसवाहन पश्चिमवक्त्रः पृथिवीतत्त्वः ब्रह्मरुपाय ह्रां पश्चिमवक्त्रवाहने विनियोग: सद्योजातः पश्चिमवक्त्राय नम आ वहयामी । वाममद्य सवितारित्यस्य वामदेव ऋषिः विष्णुर्देवता त्रिष्टुपछन्दो गरुडवाहन उत्तरवक्त्र आपस्तत्त्व विष्णुरुपाय ह्रीमुत्तरवक्त्रावाहने विनियोगो वाममद्य सवितारुत्तरवक्त्राय नम आ वाहयामि अघोरेभ्य इत्यस्याघोर ऋषि रुद्रो देवता बृहतीछन्दो वृषभवाहनो दक्षिणवक्त्रतेजस्तत्त्वो रुद्ररुपाय हूं दक्षिणवक्त्रवाहने विनियोगे अघोरेभ्यो दक्षिणवक्त्राय नम आ वाहयामि। तत्पुरुषायेत्यस्य तत्पुरुष ऋषि सूर्यो देवता गायत्रीछन्दश्ववाहनः पूर्ववक्त्राय नम आ वाहयामि । तमीशानमित्यस्येशान ऋषिः शब्दो देवता बृहतीछन्दः कूर्मवाहन उर्ध्ववक्त्र आकाशतत्त्वः श्वेतरुपाय ह्रौमूर्ध्ववक्त्रावाहने विनियोगस्तमीशानमुर्ध्व वक्त्राय नम आ वाहयामि ।
With the following five verses the invitation of Rudra is performed. With the verse: "Newly born etc." ... [Sadyojata] is the seer, Brahma his deity, the trishtubh his metre, the swan his riding animal, his face westward, the earth his element[.]... With the verse: "Wealth today, O Savitr, etc." ... Vamadeva is his seer, Vishnu his deity, the trishtubh his metre, Garuda his riding animal, his face northward, the water his element[.]... With the verse: "Homage to Rudra..." [Aghora] is his sage, Rudra his deity, the brihati his metre, the bull his riding animal, his face downward, the heat his element[.]... With the verse "We worship the primeval spirit..." [Tatpurusha] is his seer, Surya his deity, the gayatri his metre, the horse his riding animal, his face eastward, the wind his element[.] With the verse "Him who rules" ... [Ishana] is his seer, sound his deity, the brihati his metre, the tortoise his riding animal, his face upward, the ether his element[.]
Thus the direction of Five faces is as:
Sadyojata ➡ West Facing
Vamadeva ➡ North Facing
Aghora ➡ South Facing
TatPurusha ➡ East Facing
Ishana ➡ Upward Facing
These Five representations of Lord SadaShiva are also called PanchaBrahman. I discuss significance of PamchaBrahman in my answer here.
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