Saturn
THE GIANT PLANET SATURN, with its flat rings, is probably the most widely recognized astronomical image. For the classical world, Saturn was the most distant known planet. They named it after the original father of all the gods. Early astronomers noted its 29-year orbit and assumed that it moves sluggishly. Composed mostly of hydrogen, its atmosphere and structure are similar to Jupiter's, but its density is much lower. Saturn is so light that it could float on water (p.4S). Like Jupiter, Saturn rotates at great speed causing its equator to bulge outward. Saturn also has an appreciable magnetic field. Winds in its upper atmosphere can travel at l100 mph (l800 km/h) but major storms are rare. White spots tend to develop during Saturn's northern-hemisphere summer, which happens every 30 years or so, the last being in 1990. Read some facts about Saturn below, or click here.
17th Century View
In 1675 the Bolognese director of the Paris Observatory, Gian Domenico Cassini, discovered that, despite appearances, Saturn did not have a single, solid ring. He could see two rings, with a dark gap in between. His drawing, made in 1676, shows the gap, which was called the Cassini division in his honor.
Saturn and the Rings
Though Saturn's rings look solid from Earth, astronomers have known since the 19th century that they cannot be. In fact, they consist of countless individual particles, made of ice and dust, ranging in size from specks to hundreds of yards. The rings are only about 100 ft (30 m) thick, but their total width is more than 169,000 miles (272,000 km).
Changing View
Saturn's axis is tilted. Because the rings lie around its equator, they incline as the planet tilts. This means that the rings change dramatically in appearance, depending on what time during Saturn's year they are being observed (Saturn's year is equal to 29.4 Earth years). The angle of the rings appears to change according to how Saturn and Earth are placed in their respective orbits.
Model of Saturn
Planetaria and orreries are used to demonstrate the shapes and satellites of the planets. This orrery shows Saturn with the eight moons that were known in the 19th century. The model is flawed, however, because it is impossible to show the relative size of a planet and the orbits of its satellites.
Saturn's Weather Patterns
The weather patterns of Saturn's northern hemisphere were photographed from a range of 4.4 million miles (7 million km) by Voyager 2 in 1981. Storm clouds and white spots are visible features of Saturn's weather.
Seeing the Rings
When Galileo first discovered Saturn's rings in 1610, he miSinterpreted what he saw. He thought Saturn was a triple planet. It was not until 1655 that the rings were successfully identified and described by the Dutch scientist and astronomer Christiaan Huygens (1629-1695), using a powerful telescope that he built himself.
Two-Tone Moon
Iapetus is Saturn's third-largest moon, with a diameter of 892 miles (1,436 km). It is made mostly of ice. One of its strangest features is that one half of the surface is very much darker that the other. The dark area is coated with material as black as tar, which seems to have fallen on it. This picture was taken by the Cassini spacecraft. Cassini revealed a range of mountains up to 12 miles (20 km) high extending for about 800 miles (1,300 km)
Tiger Stripes
Saturn's moon Enceladus is about 310 miles (500 km) across. This false-color image of its icy surface from the Cassini spacecraft reveals a series of parallel fissures (in blue), which astronomers nicknamed "tiger stripes."Other images have shown plumes of icy droplets jetting out of these fissures from liquid water below the frozen crust. Large areas of the surface have no craters, or very few.This means that it has greatly altered since Enceladus first formed.
Facts about Saturn
- Sidereal period 29.4 Earth years
- Temperature at cloud tops -292°F (-180°C)
- Rotational period 10 hr 40 min
- Mean distance from the Sun 886 million miles/1.43 billion km
- Volume (Earth = 1) 744 • Mass (Earth = 1) 95.18
- Density (water = 1) 0.69
- Equatorial diameter 74,900 miJes/120,535 km
- Number of satellites 60