College students in Amherst, Massachusetts, register to vote shortly after Congress passed the 26th Amendment, lowering the national voting age from 21 to 18.
PHOTOGRAPH BY DAVID ARNOLD, NAT GEO IMAGE COLLECTION
This photo of a napping mother and her children in Mali was the cover of the May 1998 issue. Inside was the story of a decades-long drought and its effect on this nomadic people—just one result of our ever-warming world.
PHOTOGRAPH BY JOANNA B. PINNEO, NAT GEO IMAGE COLLECTION
Two butterflies float on water in Arizona's Ramsey Canyon Preserve. This river valley holds one of the most varied collections of species in the United States.
PHOTOGRAPH BY ANNIE GRIFFITHS, NAT GEO IMAGE COLLECTION
Hasidic men in a Jerusalem market appraise chickens to use during the kapparot ceremony the eve of Yom Kippur. In the ritual, the chicken assumes the sin of the person, before being slaughtered and later consumed in soup.
PHOTOGRAPH BY JAMES L. STANFIELD, NAT GEO IMAGE COLLECTION
A story in the April 2009 issue detailed the ruinous droughts Australia has experienced on and off for decades. Here, sisters ride in the family's truck to check on their wheat fields, which haven't seen a drop of rain in months.
PHOTOGRAPH BY AMY TOENSING, NAT GEO IMAGE COLLECTION
A rickshaw puller takes children to school in Kolkata, India. When this photo was published in April 2008, Kolkata was considering banning rickshaws completely.
PHOTOGRAPH BY AMI VITALE, NAT GEO IMAGE COLLECTION