Louis Niesten (1844 – 1920) was a Belgian astronomer working at the Brussels Royal Observatory.
In1877 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 over the Sunin1882. A second Belgian expedition (led by Jean-Charles Houzeau) 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.
Acrater on Mars was named in his honor.