Photography is a 7/24 activity. When the sun goes down there is a whole new world to photograph. A full moon lights up the landscape exactly the same as the sun, be it not quite so bright. The two shots of the falls were taken late at night with a full moon. Unless you noticed the stars in the sky, you might think these were day shoots. When the moon is gone, the sky is full of stars. I am now working to get more shots but am currently hampered by living on the edge of Silicon Valley which send way too much light up into the night sky.
If you are interested in this activity, you may try going to my night time tutorial pages which covers many aspects of night time photography.
The best reference book for the night time photographer is “Night Scape” by David Kingham. It is available as an eBook for $12 from Craft&Vision. This is a must read for all night photographers!