my $h_periods = {
    Mercury => { orbital => 0.24, rotation => 58.64 },
    Venus => { orbal => 0.62, rotation => -243.02 },
    Earth => { orbital => 1.00, rotation => 1.00 },
    Mars => { orbital => 1.88, rotation => 1.03 },
    Jupiter => { orbital => 11.86, rotation => 0.41 },
    Saturn => { orbital => 29.46, rotation => 0.43 },
    Uranus => { orbital => 84.01, rotation => -0.72 },
    Neptune => { orbital => 164.8, rotation => 0.67 },
};