Definition of "heliacally"

Ceylon has this one disadvantage for purposes of theatrical effect; she is like a star rising heliacally, and hidden in the blaze of the sun: any island, however magnificent, becomes lost in the blaze of India.

1843 November, Thomas De Quincey, “Ceylon”, in Speculations Literary and Philosophic: With German Tales and Other Narrative Papers (De Quincey’s Works; XII), London: James Hogg & Sons, page 37