An interstellar dust cloud, also known as a NEBULA, is a large cloud of gas and dust in outer space. It is composed of particles of dust, hydrogen, helium, and other ionized gases. These clouds are often visible in the night sky and can be seen with the naked eye. They are usually found in star-forming regions, where stars are born. Interstellar dust clouds can be very large, spanning hundreds of light years across. They are important for the formation of new stars and planets, and can also be used to study the structure of galaxies.