This was taken at the end of our second day of our trip to Yellowstone NP.

We had just arrived at the lodge, dumped off the luggage and ran back to the
geyser just as it erupted.

Old Faithful erupts every 35 - 120 minutes for 1.5-5 minutes, +/- 10 minutes.
The time of the next eruption depends on the duration of the previous eruption.
The longer the eruption, the longer the interval is for the next eruption.
Prior to the eruption, the water temperature at the vent is 204 degrees F or
95.6 degrees C.

The visitor center has a bulletin board of the predictions for most of the
geysers in the Upper Basin.

If interested, you can view my gallery of the first two day of the trip at : http://www.pbase.com/bryan_murahashi/day_1_and_2__travel_to_old_faithful_snow_lodge