def calculate_correlation_lengths(semimajor, semiminor):
    """Calculate the Condon correlation length

    In order to derive the error bars from Gauss fitting from the
    Condon (1997, PASP 109, 116C) formulae, one needs the so called
    correlation length. The Condon formulae assumes a circular area
    with diameter theta_N (in pixels) for the correlation. This was
    later generalized by Hopkins et al. (2003, AJ 125, 465) for
    correlation areas which are not axisymmetric.

    Basically one has theta_N^2 = theta_B*theta_b.

    Good estimates in general are:

    + theta_B = 2.0 * semimajar

    + theta_b = 2.0 * semiminor
    """

    return (2.0 * semimajor, 2.0 * semiminor)