Gayatri Jayanti is celebrated as the day when sage Vishwamitra uttered Gayatri Mantra for the first time. It is observed on the 10th Tithi (Lunar day) of the Jyestha Lunar month. This year (2015), it falls on May 27 in the US and May 28 in India.
The word Gayatri is derived from two words: 1) gaya, meaning “vital energies” and 2) trâyate, meaning “preserves, protects, grants liberation.” So, the words “Gayatri Mantra” might be translated as “a prayer of praise that awakens the vital energies and gives liberation and deliverance from ignorance.”
Gayatri mantra is not just a means of worship, it is an object of worship itself. There is no difference between the Gayatri Mantra and Ma Gayatri herself.
ॐ भूर्भुवः॒ स्वः । तत्स॑वितुर्वरे॑ण्यं भ॒र्गो॑ दे॒वस्य॑ धीमहि । धियो॒ यो नः॑ प्रचो॒दया॑त् ॥
Meaning in Hindi:
उस प्राण स्वरुप, दुःख नाशक, सुख स्वरुप, श्रेष्ठ, तेजस्वी, पाप नाशक, देव स्वरुप परमात्मा को हम अंतरात्मा में धारण करें, वह परमात्मा हमारी बुद्धि को सन्मार्ग की ओर प्रेरित करें।
Meaning in English:
We meditate on the glory of the Creator; Who has created the Universe; Who is worthy of Worship; Who is the embodiment of Knowledge and Light; Who is the remover of Sin and Ignorance; May He open our hearts and enlighten our Intellect.
It is highly beneficial to do Anushthaan (dedicated chanting of a mantra specified number of times every day) from today until Gayatri Jayanti (May 27/28). You can daily chant 1 or 3 or 5 or 11 or 21 Malas (one Mala is 108 beads).