http://www.astro.uu.nl/~nac/
Please do not confuse NCA and NAC! The NAC is an organization of which virtually all Dutch astronomers are members. It differs from foreign `clubs' such as the American Astronomical Society (AAS) in the USA and the Royal Astronomical Society (RAS) in the UK in that (i) many of its members are ex-astronomers (ii) it maintains close ties with amateur astronomers and (iii) it is run through the goodwill of its Bestuur, without any professional help. The main activities of the NAC are (i) to hold one-day scientific meetings about twice a year, (ii) to organize the annual three-day conference in May for all Dutch astronomers, (iii) to maintain a useful address book of Dutch astronomers, and (iv) to support and facilitate the teaching of astronomy at secondary schools. Foreign astronomers are welcome to join the NAC, and are regularly invited to give talks at the conference. The NCA Board also proposes astronomers for IAU membership. At present the Chair of the Bestuur is Harm Habing. Check the above-mentioned website on how to join the NAC.