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There is no mention of specific zodiac signs in the Pali Canon, as far as I know. Stars, galaxies or constellations are only mentioned generically.
Mainstream historians say the Buddha lived around 563 BCE to 483 BCE, as you can see on Wikipedia.
The traditional chronology of Theravada Buddhism can be found on this page. It says in the footnote:
Year 1 of the Buddhist Era calendar is the year of the Buddha's Parinibbana (death and final release), which occurred in the Buddha's eightieth year (480 BCE according to the "historical" timeline; 544 BCE by tradition).
The actual date of the Buddha's birth is unknown. According to Buddhist tradition, the Buddha's birth took place in 624 BCE, although some recent estimates place the Buddha's birth much later β perhaps as late as 448 BCE. 560 BCE is one commonly accepted date for the Buddha's birth, and the "historical" date for that event that I adopt here.
According to National Geographic's article "Oldest Buddhist Shrine Uncovered In Nepal May Push Back the Buddha's Birth Date" (Nov 27, 2013) by Dan Vergano:
Time to push back the Buddha's birth date a century or so? Archaeologists may have uncovered evidence of the oldest Buddhist shrine yet discovered, dating to around 550 B.C. ....
The exact date of the Buddha's birth is disputed, with Nepalese authorities favoring 623 B.C., and other traditions favoring more recent dates, around 400 B.C. ....
Digging beneath a central shrine, the researchers uncovered postholes pointing to a wooden railing surrounding a tree shrine and dating to around 550 B.C., says Coningham. They also found an older brick structure.
The videos the OP linked proposes dates which are not supported by mainstream historians. 1800 BCE is completely nonsensical for the Buddha's lifetime.
It's obvious that the Buddha lived before Adi Shankara, based on the writings of the latter. The date of 1800 BCE for the Buddha's life was fabricated so that Adi Shankara's birth date can be placed at 509 BCE based on tradition. However, mainstream historians agree that Adi Shankara was born around 700 CE or 788 CE, as you can see on Wikipedia.
I noticed a trend that certain religious scholars like to push dates far back in time, than it really is, because to them, the older something is, seems to lend credibility to it.
However, in the case of Buddhism, the dates do not matter at all. Buddhists seem to be more than happy to accept dates given by mainstream historians and archaeologists, because it doesn't change the credibility of the Buddha's teachings in their view.
In fact, accurate historical and geographical information is helpful, in understanding the context behind some of the teachings and stories told in the Pali Canon and other texts.