Se-tenant stamps are commemorative stamps printed together on the same sheet but differing in design. I was particularly thrilled to find this sheet of United Nations issued stamps issued in 2010 for the 50th anniversary of the International Oceanographic Commission
(I bought it partly because of the turtles)
It is the oceans that make life on Earth uniquely sustainable within the solar system. The sustainability of the air we breathe, the water we drink, the food we eat and the climate in which we live is dependent upon the oceans.
which ties in nicely with this set from Finland for the 2009 Europa theme of astronomy (which I was also thrilled to find)
The pair of stamps depict a fantasy landscape of lakes and different heavenly bodies. The left-hand stamp has the Moon in the centre, with the Milky Way on the right. The stamp on the right bas a comet on the left side, and a solar eclipse and showing Saturn on the right