* Astronomy

Great Northern Expedition: Empress Anna issued an Ukase on April 17, 1732
http://en.wikipedia.org/wiki/Great_Northern_Expedition#The_Expedition

The first successful VLBI observation by the Algonquin and Dominion observatories on April 17 1967
http://www.astron.nl/dailyimage/pictures/20170417/AJPOD_image_170417_plaque

Geraldine "Jerrie" Fredritz Mock was the first woman to fly solo around the world on April 17, 1964 
http://en.wikipedia.org/wiki/Jerrie_Mock

Andrei Ivanovich Borisenko (born April 17, 1964 in Leningrad, Russia) is a Russian cosmonaut.
http://en.wikipedia.org/wiki/Andrei_Borisenko

Eberhard Frederich Ferdinand Hopf (April 17, 1902 - July 24, 1983) was a mathematician and astronomer
http://en.wikipedia.org/wiki/Eberhard_Hopf

Giovanni Domenico Maraldi (April 17, 1709 - November 14, 1788) was an Italian-born astronomer
http://en.wikipedia.org/wiki/Giovanni_Domenico_Maraldi

Harold Lester Johnson (April 17, 1921 - April 2, 1980) was an American astronomer.
http://en.wikipedia.org/wiki/Harold_Johnson_(astronomer)

Giovanni Battista Riccioli (17 April 1598 - 25 June 1671) was an Italian astronomer
http://en.wikipedia.org/wiki/Giovanni_Riccioli

NGC 3356 was discovered by William Herschel on the 17th April 1784.
http://astronomy.activeboard.com/t57321029/ngc-3356/

NGC 3398 was discovered by William Herschel on the 17th April 1789.
http://astronomy.activeboard.com/t57321023/ngc-3398/

NGC 3425 was discovered by William Herschel on the 17th April 1784.
http://astronomy.activeboard.com/t57321016/ngc-3425/

NGC 3681 was discovered by William Herschel on the 17th April 1784.
http://astronomy.activeboard.com/t57320990/ngc-3681/

NGC 3684 was discovered by William Herschel on the 17th April 1784.
http://astronomy.activeboard.com/t63322793/ngc-3684/

NGC 3790 was discovered by William Herschel on the 17th April 1784.
http://astronomy.activeboard.com/t57320980/ngc-3790/

NGC 4107 was discovered by Heinrich Louis d'Arrest on the 16th April 1863.
http://astronomy.activeboard.com/t57320974/ngc-4107/

NGC 4141 was discovered by William Herschel on the 17th April 1789.
http://astronomy.activeboard.com/t57320962/ngc-4141/

NGC 4149 was discovered by William Herschel on the 17th April 1789.
http://astronomy.activeboard.com/t57320956/ngc-4149/

NGC 4161 was discovered by William Herschel on the 17th April 1789.
http://astronomy.activeboard.com/t57320940/ngc-4161/

NGC 4193 was discovered by William Herschel on the 17th April 1784.
http://astronomy.activeboard.com/t57320933/ngc-4193/

NGC 4195 was discovered by William Herschel on the 17th April 1789.
http://astronomy.activeboard.com/t57320919/ngc-4195/

NGC 4199 was discovered by William Herschel on the 17th April 1789.
http://astronomy.activeboard.com/t57320905/ngc-4199/

NGC 4454 was discovered by William Herschel on the 17th April 1789.
http://astronomy.activeboard.com/t62766542/ngc-4454/

NGC 4500 was discovered by William Herschel on the 17th April 1789.
http://astronomy.activeboard.com/t57320895/ngc-4500/

NGC 4531 was discovered by William Herschel on the 17th April 1784.
http://astronomy.activeboard.com/t57320861/ngc-4531/

NGC 4547 was discovered by William Herschel on the 17th April 1789.
http://astronomy.activeboard.com/t57320847/ngc-4547/

NGC 4550 was discovered by William Herschel on the 17th April 1784.
http://astronomy.activeboard.com/t51038016/ngc-4550/

NGC 4551 was discovered by William Herschel on the 17th April 1784.
http://astronomy.activeboard.com/t57320806/ngc-4551/

NGC 4587 was discovered by Johann Palisa on the 17th April 1882.
http://astronomy.activeboard.com/t57320797/ngc-4587/

NGC 4593 was discovered by William Herschel on the 17th April 1784.
http://astronomy.activeboard.com/t31429209/ngc-4593/

NGC 4602 was discovered by William Herschel on the 17th April 1784.
http://astronomy.activeboard.com/t57320751/ngc-4602/

NGC 4640 was discovered by Lewis Swift on the 17th April 1887.
http://astronomy.activeboard.com/t57320741/ngc-4640/

NGC 4641 was discovered by Lewis Swift on the 17th April 1887.
http://astronomy.activeboard.com/t57320732/ngc-4641/

NGC 4684 was discovered by William Herschel on the 17th April 1784.
http://astronomy.activeboard.com/t57320723/ngc-4684/

NGC 4688 was discovered by William Herschel on the 17th April 1786.
http://astronomy.activeboard.com/t57320706/ngc-4688/

NGC 4691 was discovered by William Herschel on the 17th April 1784.
http://astronomy.activeboard.com/t57320687/ngc-4691/

NGC 4713 was discovered by William Herschel on the 17th April 1786.
http://astronomy.activeboard.com/t57320681/ngc-4713/

NGC 4808 was discovered by William Herschel on the 17th April 1786.
http://astronomy.activeboard.com/t57320673/ngc-4808/

NGC 4935 was discovered by Lewis Swift on the 17th April 1887.
http://astronomy.activeboard.com/t57320660/ngc-4935/

NGC 5019 was discovered by William Herschel on the 17th April 1786.
http://astronomy.activeboard.com/t57320652/ngc-5019/

NGC 5027 was discovered by John Herschel on the 17th April 1830.
http://astronomy.activeboard.com/t57320636/ngc-5027/

NGC 5060 was discovered by Heinrich Louis d'Arrest on the 16th April 1863.
http://astronomy.activeboard.com/t57320624/ngc-5060/

NGC 5137 was discovered by Lewis Swift on the 17th April 1887.
http://astronomy.activeboard.com/t57320618/ngc-5137/

NGC 5143 was discovered by R. J. Mitchell on the 17th April 1855.
http://astronomy.activeboard.com/t57320603/ngc-5143/

NGC 5667 was discovered by William Herschel on the 17th April 1789.
http://astronomy.activeboard.com/t57320592/ngc-5667/

NGC 5678 was discovered by William Herschel on the 17th April 1789.
http://astronomy.activeboard.com/t57320580/ngc-5678/