The King James Version (KJV) of the Bible reads "Now when Jesus was born in Bethlehem of Judaea in the days of Herod the king, behold, there came wise men from the east to Jerusalem, Saying, Where is he that is born King of the Jews? for we have seen his star in the east, and are come to worship him...When they had heard the king, they departed; and, lo, the star, which they saw in the east, went before them, till it came and stood over where the young child was" (Matthew 2:1-2,9). This star seems to appear in the east.
The Book of Mormon prophet Samuel predicted this sign would happen in the New World, but with different terminology. Later, Nephi reports that the sign came to pass.
"And behold, there shall a new star arise, such an one as ye never have beheld; and this also shall be a sign unto you" (Helaman 14:5).
"And it came to pass also that a new star did appear, according to the word" (3 Nephi 1:21).
These passages indicated that the star is to "arise" or "appear" but does not mention anything about it being in the east.
Perhaps you're wondering what my point is. Perhaps this will make it clear. According to the translators of the ESV, Matt 2:1-2,9 should be translated:
"Now after Jesus was born in Bethlehem of Judea in the days of Herod the king, behold, wise men from the east came to Jerusalem, saying, 'Where is he who has been born king of the Jews? For we saw his star when it rose and have come to worship him.'...After listening to the king, they went on their way. And behold, the star that they had seen when it rose went before them until it came to rest over the place where the child was."
In other words, a new star appearing "in the east" is an idiom that means "a new star arises" or comes to be. This is reflected quite well in the Book of Mormon where it is not predicted that the start will be "in the east," but that it will "arise" or "appear." This is, at worst, another example of a lucky guess on Joseph Smith's part. At best, it is another evidence for the ancient origins of the Book of Mormon.