It is said in Scripture and Tradition that at the time of the birth or announcement of every Messenger of God, a star or a sign appears in the heavens.
Nimrod was warned of the star that told of the coming of
Abraham. The soothsayers warned Pharaoh of the star in the heavens that
foretold the coming of Moses. The Magi informed Herod of the new star that guided
them to the throne of the "spiritual king," Jesus. The same legend is
told of Buddha, Zoroaster, Muhammad and Krishna.
What were the signs in the heavens during the appearance of
the Báb and Bahá'u'lláh? The holy Scriptures of all faiths had spoken of Twin-Revelations
that would appear at the "time of the end." Now that the Báb and Bahá'u'lláh
had appeared, fulfilling these prophecies, what were the signs in the
heavens? Signs, not for one, but for two
Messengers of God, Who would appear almost simultaneously?
Some of us know the story of the great comet of 1843 which foreshadowed
the coming of the Báb.
Sir James Jeans, late British astronomer and mathematician,
stated in his book ‘Through Space and Time’, "oddly enough, many of the
most conspicuous appearances of comets seem to have coincided with, or perhaps
just anticipated, important events in history." 
One of the most unique stories of a comet is that told of
the period during which the Báb and Bahá'u'lláh were engaging correspondence,
and during which the Báb was preparing His followers for the appearance of Bahá'u'lláh.
This story was told in the stars as well as on the earth.