import math


def y2lat(y):
    """
    Translate a y-axis coordinate to longitude geographic coordinate, assuming
    a spherical Mercator projection.

    :param y: float
    :return: float
    """
    return 180.0 / math.pi * (2.0 * math.atan(math.exp(y * math.pi / 180.0)) - math.pi / 2.0)