"The International Year of Astronomy 2009 is a global effort initiated by the International Astronomical Union (IAU) and UNESCO to help the citizens of the world rediscover their place in the Universe through the day- and night-time sky, and thereby engage a personal sense of wonder and discovery.
There will be a variety of philatelic materials generated to commemorate IYA2009 specifically or feature astronomy as a theme or topic, in general." You can read more here.
Korea was the 1st country to issue stamps commemorating the year of astronomy. Here you can see the Planetary Nebula NGC 3132 which looks like a planet but is actually composed of clouds of gases and dust created by the explosion of a star’s unstable outer layer; and the Whirlpool Galaxy M51 composed of hundreds of billions of stars and interstellar matter.