Arjen Roelofs (1 March 1754 – 11 May 1828) was a Dutch astronomer. Early life Roelofs was born on the Hommema-sate (estate) near Hijum in Friesland, the youngest of four sons and two daughters. His father was Roelof Pytters, a tenant farmer and tax receiver. His mother was Neeltje Alberts from Finkum. The oldest son Klaas trained as a steersman, but did not work as one, and instead became a doctor in Sexbierum. The other sister Lisbeth married and left the household. It was not an easy life on the farm, but this is where the other three boys, Pieter, Albert and Arjen worked. Their mother stimulated the interest of the three sons in mathematics and science, however their father was unhappy with this. After their parents died in 1790, the three brothers took over the farm, and their sister Antje became their housekeeper. None of these four ever married, and they all lived on the farm until they died. Arjen Roelofs was supposed to have polio so he could not use his right leg very well, and later he could not work on the farm anymore. This enabled him to spend more time on his hobbies. His brothers joined him in his hobbies. Pieter was known as a mathematician, and was also an excellent instrument maker. Arjen designed telescopes, and Pieter made them. Albert was a clockmaker. Pieter and Arjen took meteorological measurements and made instruments to accomplish this. They made thermometers, hygrometers, and measured wind speed and wind direction. Circle of friends Eise Eisinga regularly spent time at Hijum. He ensured that University of Franeker professor Jean Henri van Swinden became a very regular visitor. Roelofs also took on students. His cousin Roel Hessels Hommema, and his friend Rinse Bearts Gelder were taught in Hijum. Later Arjen regularly worked with instrument maker and farmer Sieds Johannes Rienks of Hallum. In 1817 they presented a plan for the construction of a telescope to the Dutch Government. The plan did not eventuate. However it did interest King Willem I, who named both as Brothers in the Order of the Netherlands Lion on 23 September 1817. The brothers were also awarded a silver medal by Lodewijk Napoleon, on 20 June 1810. Arjen Roelofs made most of the calculations and measurements for Rienks for the building of the telescopes in Leiden and Utrecht. Rienks had been commissioned to build these in 1818.