The Aurora Australis or Southern Lights are only visible in Antarctica from March to September, however, there's a slim chance for tourists to see this because it's not often visible in areas in which cruise ships are allowed to land — plus, there needs to be sufficient darkness for it to be seen. As for the Southern Cross, it's visible at any time of the year; but then again, there needs to be enough darkness which is not the case during the height of the tourist season (which is summer).