Louis Niesten

Louis Niesten was a Belgian astronomer working at the Royal [Observatory of Belgium|Brussels Royal Observatory]. In 1877 he observed Mars and created a detailed map of its surface features.
He organized an expedition to Santiago [de Chile] to observe the Venus transit the Sun in 1882. A second Belgian expedition travelled to San [Antonio, Texas] to determine the planet's parallax during the same transit. Both parties used a specially designed heliometer for this purpose.
A crater on Mars was named in his honor.