Gayatri mantra is also known  as Savitri and Ved-Mata, that is " The Mother of Vedas ".

The Mantra has meaning as follows,-

O God! You are Creator of this  Universe ! You are Almighty ! Omnipresent and  Omnipotent ! You are the Light,Knowledge and Bliss.You are Destroyer of all evil and fear. You are the Greatest of all. We bow and
meditate upon Your  light. You guide our intellect in the right direction.

The scientific meaning is as follows,-

A) AUM BHUR BHUVAH SWAH:
Bhur the earth, bhuvah the planets and swah means the Galaxy. The sound  produced due to the rotation of earth, planets and galaxies is "AUM"

The  sound was experienced by Rishi Vishvamitra,during his meditation and he explained the same to other sages and rishis,who then unanimously decided to call this  sound Aum the name of God,since this sound is
available in all the three  periods of time. Therefore, it was the first  ever revolutionary idea to
identify formless God with a specific title  (form) called upadhi.
Until that time, everybody recognized God as  formless and nobody was
prepared to accept this new idea. In "Gita" also, it is said, "Omiti ekaksharam brahma", meaning that the name of the  Supreme is Aum, which
contains only one syllable (8/12).


B) TAT SAVITUR VARENYAM:
Tat  that (God), savitur the sun (star),varenyam worthy of bowing or respect. Rishi Vishvamitra suggested that we could realise the unknowable formless God through the known  factors ie sound Aum and light of stars.


C) BHARGO DEVASYA DHEEMAHI:

Bhargo the light, Devasya pertaining to the God, Dheemahi we should meditate.The rishi instructs us to meditate  upon the available form (light of
suns) to discover the formless Creator  (God). Also he wants us to perform the Japnam of the word Aum.
But the human mind is very shaky and restless  that without the blessing of Brahma, it cannot be controlled.
Hence Vishvamitra advises the way to pray to Brahma as under:

D) DHIYO YO  NAH PRACHODAYAT:

Dhiyo (intellect), Yo (who), Nah (we all),  Pachodayat (guide to right Direction). O God! Deploy our intellect on the  right path.