In 1817 he met Austrian astronomer Baron Franz Xaver von Zach, who influenced Rümker to study astronomy.

Rümker was one of a number of influential German-speaking residents — such as Ludwig Becker, Hermann Beckler, William Blandowski, Amalie Dietrich, Wilhelm Haacke, Diedrich Henne, Gerard Krefft, Johann Luehmann, Johann Menge, Carl Mücke (a.k.a.

[2] In 1821 Rümker went to New South Wales as astronomer at the observatory built at Parramatta by Sir Thomas Brisbane.

He had been granted 1,000 acres (4.0 km2) of land on the west side of the Nepean River on the assurance that he would devote his time to scientific pursuits.

Rümker also contributed an article to the Geographical Memoirs of New South Wales, edited by Barron Field, the first collection of scientific papers published in Australia.

[1] Rümker returned to Europe in 1830 and took charge of the new Hamburg Observatory after the death of Johann Georg Repsold in 1830.