James Dunlop - Observations and Discoveries in Australia

Observations and Discoveries in Australia

Dunlop made several noteworthy discoveries in the Southern Hemisphere sky and in 1828 published A Catalogue of Nebulae and Clusters of Stars in the Southern Hemisphere observed in New South Wales, which contains 629 objects. A little more than half the objects he discovered proved to be real, most being small nebulous objects being probably artificially created from the handmade reflecting telescope he had constructed himself. His most famous discovery is likely the radio galaxy NGC 5128, though he found many new open star clusters, globular clusters, bright nebulae and planetary nebulae, most previously unknown to visual observers.

Dunlop's other major observational work was of 256 southern double stars or "pairs" below the declination of about 30° South. These were listed in Approximate Places of Double Stars in the Southern Hemisphere, observed at Paramatta in New South Wales, published in 1829. Many of these pairs were actual new discoveries, though the most northerly of them had been earlier discoveries made by other observers. These double star observations were all made roughly between December 1827 and December 1828, being observed through his homemade 9-foot 23 cm (9-inch) speculum Newtonian reflector, or by measuring the separated distances and position angles of selected double stars using the small 8.0 centimetres (3.1 in) equatorial mounted refracting telescope. Most of these pairs have proved to be uninteresting to astronomers, and many of the double stars selected were too wide for the indication of orbital motion as binary stars. It seems these observations were made when the atmospheric conditions were quite unsuitable for looking at deep sky objects, either being made under unsteady astronomical seeing or when the sky was illuminated by the bright moon. John Herschel immediately on arrival in South Africa in 1834 and 1835 re-observed all of the James Dunlop's double stars, but had troubles identifying them or finding significant differences in the measured positions of the stars . He first began with Alpha Crucis / Acrux, the brightest star in the constellation of Crux, also commonly known as the Southern Cross, then systematically searched for all the others. Herschel also was first to designated all the Dunlop double stars to begin with the Greek letter "Δ", which persists in many amateur observational references. Hence, bright southern doubles like p Eridani is known as Δ5, Gamma Crucis / Gacrux is Δ124, etc. Modern double star observers have since discarded this designation and prefer the observer abbreviation "DUN", as first adopted in the Washington Double Star Catalog (WDS) as maintained by the US Naval Observatory in Washington D.C.. Hence, p Eridani is DUN 5, Gamma Crucis / Gacrux is DUN 124, etc.

James Dunlop is currently buried within the grounds of St. Paul's Anglican Church in Kincumber, New South Wales.