The winter solstice happened to cross the galactic plane in 2012.
Some New Agers reasoned that this would place the winter solstice closest to the galactic center that year, so the alignment of the sun, winter solstice, and the galactic center on the same date that the Mayan calendar predicted the end of the world was apocalyptic, and hence no coincidence.
If this date is correct, then that cycle ended on December 21, 2012.
By the mid-1970s, some New Agers had noticed the idea, and taught that the world would end on this date.
Lieder later explained that this date was “a white lie. Lieder’s choice for the name of her hypothetical planet is unfortunate, because more than a century ago, the astronomer Percival Lowell had chosen “Planet X” as the name of a possible planet lying beyond the orbit of Neptune.
The search for this Planet X resulted in the discovery of Pluto.
However, with Lieder’s connection between her Planet X and Sitchen’s Nibiru, many other people began to equate the two.
Therefore, many people now use the terms Nibiru and Planet X interchangeably.
In the minds of many people, Planet X is equated with Pluto, so Lieder’s choice has led to confusion.
While Lieder never called her Planet X Nibiru, she announced on her website in 1996 that “Planet X and the 12th planet are one and the same.”2 Given the widespread knowledge of Sitchen’s thesis, the title of his first book, and his choice of Niburu for the name of his hypothetical planet, Leider clearly intended to equate her Planet X with Sitchen’s Nibiru.
A few years ago, Nibiru came to be associated with the predicted end of the world on December 21, 2012, supposedly indicated in the Mayan calendar.
The kernel of this idea was the cycle of 5,126 years in the Mayan calendar.
Sitchen claimed that the history he revealed came from writings from Sumer and other ancient Mesopotamian civilizations; however, archaeologists and others who study the ancient Near East universally dismiss this.