Solar Dynamics Observatory (SDO)  -  Home page at NASA >Missions   -   Home page at NASA/Goddard Space Flight Center   -   on Wikipedia

Hubble Telescope website (supported by NASA?): http://hubblesite.org/   -   on Wikipedia  

National Aeronautics and Space Administration (NASA)   -   on Wikipedia  

Solar System Dynamics  -  HORIZONS Web Interface

http://www.zwartegaten.nl  is redirected to  http://www.rug.nl/sciencelinx/blackholegame/index.html; after this one-minute Flash Splash intro one finds the website itself at  http://www.rug.nl/sciencelinx/blackholegame/home.html. 
Peeling off this URL yields  http://www.rug.nl/sciencelinx/blackholegame/index, http://www.rug.nl/sciencelinx/index, and finally http://www.rug.nl/corporate/index  (One sees: Rijksuniversiteit Groningen wants to look like a corporation)

spaceweather.com:  Daily Sun; Sunspots; the Radio Sun; Coronal holes; Near-Earth asteroids; Web links; Archive  -  space weather on Wikipedia

www.astronomie.nl:  NOVA - Nederlandse Onderzoekschool Voor Astronomie / Dutch Astronomy Research School

allesoversterrenkunde.nl:  Govert Schillings website

Stichting "De Koepel"  -  Lezingen / Lectures  -  Tweedehandsboeken / Second-hand books  

ISS - INTERNATIONAL SPACE STATION   -   on Wikipedia  
ISS Waarnemingen / Observations:  http://www.heavens-above.com/   
Zichtbaarheid standplaats Rotterdam / Visibility location Rotterdam:
http://www.heavens-above.com/PassSummary.aspx?satid=25544&lat=51.917&lng=4.500&loc=Rotterdam&alt=-4&tz=CET  
Zichtbaarheid standplaats Kaapstad - Green Point / Visibility location Cape Town - Green Point:
http://www.heavens-above.com/PassSummary.aspx?satid=25544&lat=-33.90462&lng=18.40982&loc=Cape-Town&alt=0&tz=CET  

Satellite Flybys at Rotterdam, NL from spaceweather.com