ASTRONOMY MYTHS. The myth that the world will end in December 2012 started with claims that Nibiru, a supposed planet discovered by the Sumerians, is heading toward Earth. Zecharia Sitchin, who writes fiction about the ancient Mesopotamian civilization of Sumer, claimed in several books (e.g. The Twelfth Planet, The Stairway to Heaven, The End of Days) that he has found and translated Sumerian documents that identify a planet Nibiru orbiting the Sun every 3,600 years. Sitchin's Sumerian fables include stories of astronauts visiting Earth from an alien civilization called the Anunnaki.
After these books appeared, Nancy Lieder, a self-declared psychic, wrote on her web site ZetaTalk that the inhabitants of a fictional planet orbiting the nearby star Zeta Reticuli warned her that Earth was in danger from Nibiru. The prediction said the collision of Nibiru and Earth would occur in May 2003.
Some people claim NASA found Nibiru in 1983 using the Infrared Astronomy Satellite (IRAS), which carried out a 10-month sky survey. IRAS cataloged 350,000 infrared sources, and initially many of these sources were unidentified. Astronomers have followed up all of these observations with more powerful instruments both on the ground and in space.
When nothing happened in that month, claimants moved the doomsday date forward to December 2012. Only recently have people linked these two fables to the end of the Mayan long-count at the winter solstice in 2012 hence the predicted doomsday date of December 21, 2012.