Here is the coin and some of the details about it.
Denomination: 5 hryvnia (currency of Ukraine)
Weight: 16.54 g
Diameter : 35 mm
Quality: special uncirculated
Mintage: 45 000
Designers: Volodymyr Taran, Oleksandr Kharuk, Sergei Kharuk.
Authors of models: Anatoly Demyanenko, Sviatoslav Ivanenko
I ordered the coin through Ebay, which is of course the best shopping center out there online and it took around 2 weeks for the arrival of the coin via snail-mail.Still you can order the coin and it costs less than 12 USD in total including shipping as well, Although I have searched for the other commemorative coins of other countries, Ebay didn't seem to have them on sale; of course they can be bought online at different numismatic stores but at very expensive rates.
If you're a regular visitor to this blog you must have noticed that Australia, Austria, Canada, Malaysia, Cook Islands, Greece..etc have issued official commemorative coins in celebration of the International Year of Astronomy 2009.
Additionally you can find a complete archive about all the official commemorative coins of IYA2009 though the IYA2009 Coin Blog that I've published.
However I have not given up my numismatic thirst and am always on lookout for the rest of the coins to be collected.