Gayatri Mantra - as known to everyone
ॐ भूर्भुव: स्व: तत्सवितुर्वरेण्यं । भर्गो देवस्य धीमहि, धीयो यो न: प्रचोदयात् ।।
Aum Bhur Bhuvah Swah, Tat Savitur Varenyam
Bhargo Devasya Dhimahi, Dhiyo Yo Nah Prachodayat
Gayatri Mantra is one of the very famous mantras prevalent in Hinduism. It is a highly regarded mantra. To the masses it is known to exist in a scripture called Taittiriya Aranyaka and this is where it has been written and described wrongly. The actual correct mantra is described in the Yajurveda.
Actual Gayatri Mantra in Yajurveda
भूर्भुव: स्व: तत्सवितुर्वरेण्यं । भर्गो देवस्य धीमहि, धीयो यो न: प्रचोदयात्
Bhur Bhuvah Swah, Tat Savitur Varenyam
Bhargo Devasya Dhimahi, Dhiyo Yo Nah Prachodayat
Yajurved Adhyay 36, Mantra 3 - The actual Gayatri Mantra is given in Yajurveda and it does not have "Om" (ॐ) in the front. There is no mention of "Om" in the mantra anywhere. By putting "Om" in front of the mantra, it actually becomes useless. As mentioned in Gita Ji Adhyay 8 Shlok 13, "Om" mantra is the sole mantra for jaap of God 'Brahm' and Vedas are describing the glory of Param Akshar Brahm, the Supreme/Complete God. So, this Mantra 3 of Adhyay 36 of Yajurved is praising the Supreme God, Param Akshar Brahm. Putting "Om" in front of it would be like addressing the Prime Minister as Chief Minister, which will be an insult to him.