Our galaxy is an SBbc medium size and mass spiral type. It is only partially visible, since we are inside it; the plane of the disk and the thousands of stars it contains appear to us as a milky white stripe on the celestial vault, called the Milky Way. The Galaxy is composed of a central core, a bulge, a disk and a halo. In particular, the disc contains the spiral arms. The spiral nature of the Milky Way was confirmed through the study of the distribution of the HII regions, consisting mainly of bright nebulae of ionized hydrogen (HII) that form right inside the spiral arms. The spiral arms are regions of active formation of new stars, dominated by young stars, dust and gas.

In this conference paper, we present the development of radio astronomy in Hong Kong in 21 cm wavelength since 2006. We discuss the subtropical region with its usual cloudy condition in Hong Kong for launching radio astronomy. The MIT small radio telescope and Italy SPIDER radio telescope series were good starting points to create radio astronomy for a dense human populated region like Hong Kong. We present some interesting results with respect to these two types of radio telescopes. We also introduce the future possibility for the developing radio interferometry array in Hong Kong for research and teaching.