First some definitions:

Factory

A class that generates instances of other classes, choosing which class to build on the basis of run-time information.

Façade

A class that acts as a front-end for one or more other classes, delegating the actual work to those classes as appropriate.

In your particular example, what you want is a factory: a class that generates objects according to where the sun rises. For example:

# Rational helper class...

package Astro::Data::Scientific;

use base Solar::Data;
use base Lunar::Data;

# <define methods here>



# "Differently rational" helper class...

package Astro::Data::Mythological;

use base Astrological::Data;        # Pre-empt normal methods
use base Astro::Data::Scientific;

# <overload any methods here that the 
#  heavens dictate should behave differently>



# Factory class...

package Astro::Data;

# Constructor returns instances of helper classes,
# depending on run-time astro[nl]o[mg]ical conditions

sub new {
    shift; # off class name

    if ($sun_rises_in_west) {
        return Astro::Data::Mythological->new(@_);
    }
    else {
        return Astro::Data::Scientific->new(@_);
    }
}

# <no methods of its own, since it's never actually instantiated>
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