Most nebulae are of vast size; some are hundreds of light-years in diameter. A nebula that is visible to the human eye from Earth would appear larger, but no brighter, from close by. The Orion Nebula, the brightest nebula in the sky and occupying an area twice the diameter of the full Moon, can be viewed with the naked eye but was missed by early astronomers. Although denser than the space surrounding them, most nebulae are far less dense than any vacuum created on Earth – a nebular cloud the size of the Earth would have a total mass of only a few kilograms. Many nebulae are visible due to fluorescence caused by embedded hot stars, while others are so diffuse they can only be detected with long exposures and special filters. Some nebulae are variably illuminated by T Tauri variable stars.
Nebulae are often star-forming regions, such as in the “Pillars of Creation” in the Eagle Nebula. In these regions the formations of gas, dust, and other materials “clump” together to form denser regions, which attract further matter, and eventually will become dense enough to form stars. The remaining material is then believed to form planets and other planetary system objects.
The original goal of Cassini-Huygens was to study Saturn and its large, misty, tortured, moon Titan. Titan, the second-largest moon in our Solar System, after Ganymede of Jupiter, is a world long-shrouded in mystery, hiding behind a thick orange veil, and slashed with hydrocarbon lakes and seas. However, there are other enticing moons known to circle the ringed planet. Saturn's mid-sized icy moons (Mimas, Enceladus, Tethys, Dione, Rhea, Hyperion, Iapetus, and Phoebe) are enchanting worlds. Each one of these frozen little moons reveals an interesting and unique geology. So far, Saturn is known to sport 62 icy moons!
Unfortunately, the various economic troubles which are plaguing Europe has caused ESA to spend less money than before, so many space programs in Europe has halted. However, both in China as well as in India, there are several ambitious programs present, which may cause any one of these nations to send another man to the moon in the next decade. Naturally, only time will tell; but nothing will change the fact that mankind's future is in the stars.
Organic dust forms when organic molecules, resulting from the interaction of sunlight with methane, grow large enough to tumble down to the surface of Titan. Dr. Roderiguez continued to explain that, even though this is the first-ever observation of a dust storm on Titan, the discovery is not especially surprising.