Basically, Jewish tradition holds that the sun was created on the fourth day of creation, which was a Tuesday night leading into Wednesday morning. (Remember that Jewish days start on sundown the night before.) The theory as I understand it is that every 28 years, the sun returns to its position in the sky where it was when it was created. When this happens, tradition calls for us to recite a standard blessings of experiencing wonders of nature, which in English says, "Blessed are you, Lord our God, ruler of the universe, who does the work of creation." This blessing is also supposed to be recited when one experiences an earthquake, sees lightning, witness a comet, etc. (The Transit of Venus also counts.)
Anyway, tomorrow morning Jews all over the world will be reciting Birkat HaChamah, connecting us with generations past and generations to come. We last recited this blessing on April 8, 1981, and we won't do it again until April 8, 2037.
This year is even more special, as the blessing is being recited on Erev Pesach, or the day before Passover. According to one of the references I found, the only previous years in which this happened were 609, 693, 1309, and 1925 (C.E.). The same reference says that there's a tradition that the final redemption will occur after an Erev Pesach Birkat HaChamah, so who knows? Maybe Elijah will bring special tidings on the night of the first seder.
For more and probably better information on Birkat HaChamah, please see:
Birkat Hachamah: Blessing the Sun
Wikipedia: Birkat Hachama
Quick Guide to Birkat Hachama