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10) Astronomy research goes on 24 hours per day, around the world and out to the edge of the Universe.
9) Do you like to stay up late? This is the science for you.
8) Astronomy is probably the oldest science. Every time we look to the skies, we share a moment of wonder with our earliest ancestors.
7) Astronomy is also one of the most gender-integrated sciences and has lots of creative efforts underway to attract more minorities. Astronomers collaborate from all over the world, so it is very geographically diverse too.
6) Astronomical research requires observations taken both from the ground and from space to answer most of the big questions.
5) Astronauts do it too! From the surface of the Moon to telescope platforms carried in the Shuttle cargo bay.
4) Between the lack of a clearly identified particle that comprises dark matter to the mind-expanding puzzle of dark energy, we have no real clue about the composition of 96% of the Universe.
3) Observatories are generally located amid some of the most beautiful natural scenery on Earth. And you get to look up at some of the most beautiful scenery off the Earth!
2) Astronomers are cocky enough to think that they can do things like demote Pluto from planetary status by a vote of the partial membership of one professional society, yet they are also some of the quirkiest and most lighthearted scientists around.
1) Amateur astronomers and everyday "citizen-scientists" make important contributions to current research questions, and these opportunities are expanding. See Galaxy Zoo, GLOBE at Night, or the new "Citizen Sky" Epsilon Aurigae variable-star observation campaign and get involved!
For another take on this topic, more focused on why stargazing is cool, see this podcast from the IYA2009 "365 Days of Astronomy" daily series.