Thomas Gwyn Empy Elger (27 October 1836 – 9 January 1897) was an English lunar mapper and the first director of the Lunar Section of the British Astronomical Association (BAA). Elger was a member of several astronomical associations, such as the Royal Astronomical Society, the short-lived Selenographical Society and the British Astronomical Association. Besides his astronomical work, he was an ardent archaeologist and founded the Bedfordshire Natural History Society and Field Club. He is remembered by the lunar crater Elger.
He was born in Bedford, where the family had been established for several generations. His father Thomas Gwyn Elger (1794 – 4 April 1841) was an architect and builder. Grandfather, father and son engaged in town politics, and all held the post of mayor.
He studied at University College London and adopted the profession of a civil engineer. He was engaged in several important works, including the Metropolitan Railway and the Severn Valley Railway. His surveys for railway construction in Holstein were put to a stop by the wars between Prussia, Denmark and Austria in 1864.
Soon afterwards he relinquished the active pursuit of his profession and devoted himself to scientific studies. He had developed a strong taste for astronomy already at an early age and erected his first observatory in Bedford. Elger observed with an 8.5 inch reflector. His sketches from 1884 to 1896 are now in the possession of the BAA. He is best known as a careful and indefatigable selenographer, and for this work his artistic skill eminently qualified him.
He is most remembered for his book The Moon: A full Description and Map of its Principal Physical Features. Published in 1895, its maps are still highly regarded by lunar observers due to their uncluttered nature.
At the meeting of 1896-04-28 Mr. A. Elvins presented the Society a copy of the new map of the Moon by T. Gwyn Elger. The thanks of the Society were due to Mr. Elvins for this which would be of great service to the Lunar Section in the study of the Moon. At the meeting of 1896-07-07 Mr. T. Gwyn Elger was duly elected a corresponding member of the Astronomical and Physical Society of Toronto.