Om mani Padme hum is used by Tibetan monks right? I like chanting the mantra internally..somehow all thoughts are set aside.and makes me focus on something..

Hello there...  Has anyone had experience with the Gyatri Mantra?  Any information you could offer would be helpful

I've been told that mantras ending in the "ah" sound are especially impactful.  Any thoughts?

Namaskaar,
if by "ah" you mean the 'visarga' like in Namah Shivaaya.
then i may be able to share my learning.
the sound 'ah' is a vowel in sanskrit and is called the visarga.
it has the effect of opening up our Heart chakra so that the Deity we are praying to can take a seat in it.
this has powerful effect if we add visualisation in addition to chanting the mantra.
Here we have to visualise the heart opening up at the sound of 'AH' and the deity taking her/his seat inside it.

vivek

Namaskaar,
I have been taught that Gayatri is the name of the metre in which a mantra is written.
This is one of the Chandas in which Vedic mantras are written.
A Gayatri metre consist of 3 padas (foot steps) and each pada is of eight letters (Sanskrit letters). Any mantra fulfilling this criteria is a Gayatri mantra. The Rig Veda is full of such mantras.
What is normally referrred to as the Gayatri mantra is actually the Savitur (Sun) Gayatri, Here the word Savitur means 'Prasava kaaraka Devata' or the deity which creats and this is the Sun in our physical universe.

The mantra was revealed to Rishi Vishwamitra and hence he is the Rishi for this mantra.
If you count the leters in Savitur Gayatri you will find only 23, whereas for it to be a Gaayatri it should be 24?

The best time for recitation of this mantra is during the Sandyaa (junction points during the day), the first is the junction of the night and morning, second is when it is mid-day. third when day and night meet in the evening and last is mid-night.
the fourth sandyaa is only for the SANYASIS and not for householders.

these four sandhyaas correspond to the four quadrants in the horoscope.

vivek